Rozprawy doktorskie na temat „Colloidal Experiments”

Clay mineral particles have been widely used to prepare colloidal suspensions, certain clay mineral have a rod-like shape. Colloidal suspensions of thin rods are known to show nematic phases, provided that particles are well stabilised against attractive interactions. At low concentrations such suspensions are in the isotropic phase; the nematic phase can be found upon increase of concentration. In addition, isotropic configurations at volume concentrations similar to the ones in the nematic phase can be generated for thin rods. In these systems the particles are trapped in a disordered configuration called random packing. The present thesis studies the preparation of colloidal suspensions of rod-like particles as well as the bulk properties of systems composed of rod-like particles. Rod-like particle suspensions were prepared using sepiolite clay. The stabilisation of sepiolite particles in a non-polar solvent using a combination of surfactant and polymer treatment is reported. Here the effect of polar molecules, including water, on the surface of the treated clay particles is discussed. It is found that the effect of polar molecules on the bulk properties of the final suspensions is not negligible. The isotropic-nematic phase transition mechanism for polydisperse thin rods is also studied in this work using confocal microscopy. The samples studied have a large gap in concentration between the coexisting isotropic and nematic phases, that results from polydispersity. The time evolution of the phase separating samples was recorded using confocal images. Such images were binarized to identify isotropic and nematic regions in each image. Information on the structure was obtained from the binarized images. The phase separating samples did not show nucleation and growth, even at low concentrations. Instead, they phase separated via a percolating network formed by a transient "non-sticky gel". The behaviour observed in this work is most likely related to the high polydispersity of the particles used. Random packings of rod-like particles were generated using computer simulations of hard spherocylinders. An existing algorithm was modified and the new version produced reliable results with fewer adjustable parameters. The random packing configurations obtained were somewhat more dense than those reported previously. The same algorithm was applied to mixtures of hard spherocylinders and hard spheres. However, in this case the configurations obtained showed signs of order.

Doctor of Philosophy
Department of Physics
Bruce M. Law
Three diverse first author surfaces science experiments conducted by Sean P. McBride 1-3 will be discussed in detail and supplemented by secondary co-author projects by Sean P. McBride, 4-7 all of which rely heavily on the use of an atomic force microscope (AFM). First, the slip length parameter, b of liquids is investigated using colloidal probe AFM. The slip length describes how easily a fluid flows over an interface. The slip length, with its exact origin unknown and dependencies not overwhelming decided upon by the scientific community, remains a controversial topic. Colloidal probe AFM uses a spherical probe attached to a standard AFM imaging tip driven through a liquid. With the force on this colloidal AFM probe known, and using the simplest homologous series of test liquids, many of the suspected causes and dependencies of the slip length demonstrated in the literature can be suppressed or eliminated. This leaves the measurable trends in the slip length attributed only to the systematically varying physical properties of the different liquids. When conducting these experiments, it was realized that the spring constant, k, of the system depends upon the cantilever geometry of the experiment and therefore should be measured in-situ. This means that the k calibration needs to be performed in the same viscous liquid in which the slip experiments are performed. Current in-situ calibrations in viscous fluids are very limited, thus a new in-situ k calibration method was developed for use in viscous fluids. This new method is based upon the residuals, namely, the difference between experimental force-distance data and Vinogradova slip theory. Next, the AFM’s ability to acquire accurate sub nanometer height profiles of structures on interfaces was used to develop a novel experimental technique to measure the line tension parameter, τ, of isolated nanoparticles at the three phase interface in a solid-liquid-vapor system. The τ parameter is a result of excess energy caused by the imbalance of the complex intermolecular forces experienced at the three phase contact line. Many differences in the sign and magnitude of the τ parameter exist in the current literature, resulting in τ being a controversial topic.

Río Tinto provides ideal conditions for studying the role of colloidal particles in concentrating elements and their influence on the transport of them to Ría de Huelva estuary(Spain).Ultrafiltration experiments were developed on the Río Tinto waters,in order to separate colloids by different sizes(50,10,5 and 3kDa).Samples from 50kDa and 3kDa ultrafiltration were analysed to find concentration using ICP-MS,and radionuclides activities have been determined for each of them.An ultrafiltration permeation model describes the relation between log of concentration of the element in the permeate solution and log of CF.If the permeation is constant,the linear pattern resulting can be used to predict the ultrafiltration behaviour of U and Th in this peculiar waters.Experiments were carried out using CF from 1,07 to 1,73.The behaviour of U can be predicted by a permeation model that provides a Pc of 0,813 for U(50kDa) and Pc=0,626 for U(3kDa).The permeation model can just show little retention for U,and that the permeation behaviour of U can be considered the same even at low CF.The application of the permeation model on Th(50kDa) samples failed,the membrane was not retaining quantitatively.A Pc=0,360 for Th(3kDa) was derived.Anyway,this could be due to artefactual retentions.Using low CF,colloidal concentration cannot be estimated by the permeation model for both U and Th.Concentration of U amounts to 4,73-6,54 μg/L,the range for Th is 13,0-28,0 μg/L.Both the elements are in higher concentrations respect to common natural waters,according to their predict character in acidic conditions,in which both can stay in dissolved form,and even colloids will be disintegrated. 234U/238U AR range is 1,761-2,060.The disequilibrium among 234U and 238U isotopes is attributable to the excess of 234U related both to the recoil effect,and the preferential leaching of 234U.230Th activity range is 0,056-0,169 mBq/L;its presence in solution is related to the decay of 234U.

Esta Tesis tiene como objetivo dar al lector una idea sobre las nuevas perspectivas abiertas en la manipulación controlada de Metal-Organic Frameworks con precisión nanométrica y sus consecuencias en las propiedades finales y aplicaciones. El presente estudio se propone crear un puente entre MOFs y Nanotecnología; es decir, enlazar las propiedades clásicas de los MOFs con nuevas funcionalidades que pueden emerger gracias a la manipulación a la nanoescala. Este puente entre los dos campos se ha llevado a cabo con un MOF icónico, llamado Zeolitic-Imidazolate Framework-8 (ZIF-8), uno de los MOFs más estudiados, debido su fácil síntesis su alta porosidad y gran estabilidad térmica, química y hidrolítica. La Tesis está organizada en dos partes. En el primer capítulo, que corresponde a la primera parte, el lector encontrará una introducción al concepto de la porosidad con ejemplos de materiales porosos naturales. Este capítulo continua con una breve presentación de los MOFs y una extensa introducción al ZIF-8. A través de ejemplos y conceptos especialmente seleccionados, esta introducción trata de captar la atención del lector en el principal argumento de la presente tesis, la manipulación de los MOFs a la nanoescala con el objetivo de ir más allá de sus propiedades clásicas. La segunda parte de la tesis se inicia con la descripción de los objetivos en el Capítulo 2. Los capítulos 3, 4 y 5 incluyen cada una, una publicación relacionada con la manipulación de MOFs a la nanoescala, usando el ZIF-8 y –en otros casos- otros MOFs. En estos estudios hemos seguido principalmente tres aproximaciones: 1. La aproximación post-sintética de tipo Top-Down; 2. La aproximación de tipo Bottom-Up y 3. La modulación y el auto-ensamblaje de partículas. La publicación en el capítulo 3, vinculada a la aproximación post-sintética de tipo Top-Down, presenta la modificación controlada de las formas cristales de ZIF-8, para llegar a formas no alcanzables por procesos convencionales, a través de un ataque químico. Esta publicación trata de explicar el mecanismo que subyace en este “cincelado” anisotrópico de los cristales de ZIF-8. Para demostrar la posibilidad de generalizar este método con otros MOFs, también se presenta en esta publicación el “cincelado” anisotrópico de cristales de ZIF-67. La segunda publicación que corresponde al capítulo 4, está centrada en la aproximación post-sintética bottom-up, gracias a la cual el tamaño, la forma, la composición y la arquitectura del ZIF-8 y el ZIF-67 son modificadas con métodos de química húmeda. Esta publicación muestra la manipulación de los cristales de MOF a través del crecimiento paso a paso de otros MOFs, la funcionalización de partículas de MOFs con nanopartículas inorgánicas (InNPs) y finalmente, el diseño de un material compuesto MOF-InNP multicapa que puede ser usado como catalizador en reacciones de tipo cascada. La última publicación de esta tesis, en el capítulo 5, está en relación con la moducalción in-situ y el auto-ensamblaje de partículas de MOF. Esta publicación incluye la producción de partículas de MOF de tamaño y forma altamente monodispersa usando diferentes mudladores y surfactantes. En este sentido, partículas de ZIF-8 y UiO-66 altamente monodispersas con tamaños y formas diferentes se han producido usando el CTAB y el PVP, respectivamente, con índices de polidispersidad inferiores al 5 % para el ZIF-8 y el 8 % para el UiO-66. Esta publicación también incluye el autoensamblaje coloidal de estos cristales de MOF, a través del método de evaporación rápida, en superestructuras ordenadas en redes cristalinas bien definidas que se pueden usar como cristales fotónicos 3D. Finalmente, las propiedades fotónicas de estos cristales fotónicos de MOF y su uso como sensores de alcohol han sido estudiados.
The present Thesis aims to give the reader new insights on the controlled manipulation of Metal-Organic Framework (MOF) materials with nano-scale precision and its consequences in the final properties and applications. The study presented here hopes to form a bridge between MOFs and Nanotechnology; which means, bridging the classical expectations from the bulk properties of MOFs with novel functions that can arise upon the manipulation at the nano-scale. Here we demonstrate this bridging with a prototypical MOF, namely Zeolitic-Imidazolate Framework-8 (ZIF-8), which is one of the most studied MOF, due to its easy synthesis and promising properties including high porosity and exceeding thermal, chemical and water stability. The Thesis is organized into two parts. Chapter 1 constitutes the first part where the reader will find an introduction of the concept of porosity, with examples of naturally porous materials. This Chapter continues with a brief introduction of MOFs, an extensive introduction to ZIFs and, even more extensive introduction to ZIF-8. Thanks to the carefully selected examples and concepts, this introductory Chapter attempts to draw attention of the reader to the main point of this Thesis, which is the manipulation of MOFs at the nano-scale in order to reach beyond the classical aspects. The second part of this Thesis starts with a description of the objectives in Chapter 2. Then, each chapters 3, 4 and 5 includes a publication related to the manipulation of ZIF-8 at the nano-scale using ZIF-8 and -in some cases- other MOFs. In these studies, we followed three main approaches: 1. Post-synthetic top-down approach; 2. Post-synthetic bottom-up approach; and 3. In-situ modulation and self-assembly of particles. The publication in Chapter 3 is related to the post-synthetic top-down approach, explaining the anisotropic etching of ZIF-8 crystals to reach unprecedented shapes that are unachievable by conventional synthetic methods. The publication also attempts to explain the underlying mechanism of this anisotropic etching of ZIF-8 crystals. Also, to shed light on other MOFs and to prove the generality of the method, anisotropic etching of ZIF-67 crystals is demonstrated. The second publication, which constitutes Chapter 4, is centered on the post-synthetic bottom-up approach where the size, shape, composition and architecture of ZIF-8 and ZIF-67 crystals are modified using post-synthetic wet-chemistry. This publication explains the manipulation of MOF crystals by post-synthetic growing steps of other MOF layers, the functionalization of MOF particles with inorganic nanoparticles (InNPs) and finally, the design of complex multi-layered MOF-InNP composite materials that can be used as catalysts in cascade reactions. The last publication presented in this Thesis, in Chapter 5, is related to the in-situ modulation and self-assembly of MOF particles. This publication includes the production of MOF particles with very high size and shape monodispersity using surfactants as modulators. In this sense, highly monodisperse ZIF-8 and UiO-66 particles with various sizes and shapes were produced using CTAB and PVP, respectively, with polydispersive index < 5% for ZIF-8 and < 8% for UiO-66. It also includes the colloidal self-assembly of these MOF crystals via a fast droplet evaporation method to form ordered superstructures with well-defined crystalline superlattices that can be used as 3D photonic crystals when the particle size is selected appropriately. Finally, the photonic properties of these MOF photonic crystals and evaluation of this sensing capability of alcohol vapors are exploited.

To get a complete scenario of the rheological behaviour of non-colloidal suspension it is important to explore the transient shearing, elongational, and oscillatory shearing as well as simple steady shearing. The thesis includes new experiments and comparisons with the few theories available. The simple steady shearing and elongation flow behaviour of non-colloidal suspensions were studied. Simple shear-thinning effects were discussed and the elongational phenomena in non-colloidal suspensions were investigated, where transient shearing was also considered. The thinning effects in non-colloidal suspension were studied from different experiments and simulations. Shear-thinning was clear on 40% volume fraction suspensions. The shear-thinning depends on the variation of the interparticle friction coefficient with the shear rate or shear stress. The transient result did not replicate Gadala‐Maria and Acrivos (1980) results. They performed their test 40 years ago using similar suspensions and we believe the variation may be due to the better performance/sensitivity of the newer rheometers. We developed a new setup to perform the elongational test and the motion of the fluid drops was filmed with a high-speed FASTCAM PCI R2 (Photron) camera. The reduction in diameter of the drop with time indicates the elongation rate; pure elongation was seen where the diameter was minimum. To investigate the changes in elongational viscosity of 12500 cs Silicone oil suspension, a steel ball was introduced with the suspensions this improves the filament shape – it is more uniform. We assumed the rate of elongation (ε ̇) was constant over the cross-section (but varied at different times); the rate of elongation was then found using the variation in diameter with time (Dai and Tanner, 2017). Friction plays a significant role in non-colloidal suspension and it becomes more complex at higher concentration of suspension. A “bootstrap” feedback model was proposed (Tanner et al., 2018) which shows how friction amplifies the stress and increases the complexity of the suspension behaviour. The bootstrap mechanism of friction enhancement in non-colloidal suspensions appears to be a useful idea. In view of the confusing picture reported by others, it was decided to make further measurements of small and medium strain oscillatory flows keeping in mind possible friction between particles. Because of the observed tendency to hysteresis, the oscillatory flow was combined with the parallel steady shear flow to control or eliminate hysteresis. The response of concentrated suspensions under oscillatory shear is surprisingly complex, and it becomes more complex when oscillatory shearing and steady shearing are combined. The non-zero storage modulus experienced due to frequency sweep tests in a glycerine matrix was an apparent storage modulus which was due to inertia effects (which were very small). We observed a slight decline in G^' and G^'' with an increase of strain amplitude and we believe settling is not responsible. Surprising hysteresis effects were experienced by both moduli with increased and decreased strain amplitude. The hysteresis was more dominant in the storage modulus than in the loss modulus and at higher concentrations the effect was severe. In simple steady shearing, friction increases the suspension viscosity, and we believe both G^' and G^'' also increase due to friction. The effect of variable oscillatory shear stress and steady shear stress was analysed and a model for superposed storage modulus, loss modulus and viscosity responses was proposed. Frictional effects were considered in the proposed model and satisfactory fitting with the experimented data was observed. The ‘bootstrap’ feedback mechanism was adapted to explain frictional effects. We proposed a universal model for non-colloidal suspensions. This is a modified Reiner-Rivlin inelastic model (eq. 5.9) which is a reasonable description of available tests of suspensions with Newtonian matrices in several flows for larger strains. Further checks are needed, and the quest must continue for more basic understanding. Nevertheless, the modified Reiner-Rivlin model is simple to apply and should be useful for numerical work on the concentrated suspensions.

In this thesis ultrafast exciton dynamics of several colloidal quantum dots have been studied using visible transient absorption spectroscopy. The resultant transient decays and differential transmission spectra were analysed to determine the ultrafast relaxation channels, multiple exciton generation (MEG) efficiency and multi-exciton interactions in the observed materials. All QDs were preliminarily optically characterized using steady state absorption and photoluminescence spectroscopies. In addition, a high repetition infrared femtosecond pump probe experiment was designed and built to detect the picosecond intraband carrier relaxations in quantum dots. Picosecond carrier dynamics of type-II ZnTe/ZnSe and of CuInSe2 and CuInS2 type-I quantum dots were investigated. The common feature of these materials is that they are eco-friendly materials, being alternatives to the toxic Cd- and Pb- based materials. It was found that surface trapping occurred in both cases for electrons in the hot states, and in the minimum of the conduction band for ZnTe/ZnSe core/shell materials. Trion formation was observed in ZnTe/ZnSe core/shell dots at high power and unstirred conditions. The hot and cold electron trapping processes in type-II dots and CuInS2 and CuInSe2 dots shifted, distorted and moderately cancelled the bleach features. In addition, intra-gap hole trapping was observed in CuInS2 and CuInSe2 dots which results in a long decay feature in the recorded transients. MEG competes with Auger cooling, surface mediated relaxation and phonon emission. To enhance the MEG quantum yield, the rival mechanisms were suppressed in well-engineered CdSe/CdTe/CdS and CdTe/CdSe/CdS core/shell/shell and CdTe/CdS core/shell type-II quantum dots. The MEG slope efficiency and threshold for a range of different core size and shell thickness were found to be (142±9)%/Eg and (2.59±0.16)Eg, respectively. The observed threshold was consistent with the literature, whereas, the obtained slope efficiency was about three times higher than the previously reported values. The biexciton interaction energy of the dots stated in the previous paragraph was also studied. To date, time-resolved photoluminescence (TRPL) has been employed to study exciton interactions in type-II quantum dots and large repulsive biexciton interaction energy values between 50-100 meV have been reported. However, unlike the TRPL method, the TA experiment ensures that only two excitons remain in the band edge of the dot. Using this method, large attractive biexciton interaction energies up to ~-60 meV was observed. These results have promising implications regarding enhancing the MEG quantum yield.

Les dispersions col·loïdals, un terme encunyat pel científic escocès Thomas Graham el 1861, han estat objecte d’interès en diferents àrees científiques durant més d'un segle. Una dispersió col·loïdal es caracteritza per l’existència d'una fase dispersa uniformement distribuïda dins un medi dispersiu. Diferents compostos entren dins aquesta categoria, com els aerosols (fum, boira, núvols o pols), les escumes, les emulsions (maionesa o llet) o els gels (mantega o melmelada). Les millores recents en la síntesi de partícules i l'estabilitat col·loïdal han impulsat la millora en el disseny de nous col·loides, conferint-los les propietats requerides en cada aplicació. Entre la gran varietat de dispersions col·loïdals (existents en la naturalesa o dissenyades per l'home), hem estudiat un tipus singular de dispersions on les partícules col·loïdals mostren un comportament superparamagnetic anomenades dispersions col·loïdals superparamagnètiques. En aquestes dispersions, sorgeixen característiques sorprenents quan un camp magnètic extern és aplicat, com a conseqüència del balanç entre les interaccions característiques entre col·loides i la interacció magnètica anisotròpica dipol-dipol entre les partícules col·loïdals constituents. Al llarg d'aquesta tesi s'ha utilitzat diferents models teòrics i de simulació per tractar diferents fenòmens que apareixen en aquestes dispersions col·loïdals superparamagnètiques. Per una banda, hem mostrat com l’aplicació de camps magnètics uniformes a aquestes dispersions indueix l’agregació reversible de les partícules superparamagnètiques. A la vista dels models teòrics i simulacions, hem proposat un nou criteri basat en les propietats físiques de les dispersions col·loïdals per predir la formació d'agregats, i la seva validesa s'ha discutit comparant el comportament predit amb resultats experimentals. Hem aportat evidencies de la existència d'un estat d'equilibri on els agregats assoleixen una distribució de mides estable, un fet ja suggerit amb anterioritat però establert sense prou claredat. També ens hem centrat en la descripció de la cinètica de creixement d'aquests agregats i en la seva implicació en diferents fenòmens observats experimentalment. La necessitat d'assolir escales de temps grans, com en certes situacions experimentals, ha motivat el desenvolupament de nous models i estratègies de simulació per reduir els temps de càlcul requerits en simulacions estàndard. Hem presentat un nou model de simulació que proporciona un mètode fiable i més ràpid per descriure la formació d'estructures en forma de cadena que apareixen en dispersions superparamagnètiques. El model ha estat validat comparant-ne els resultats obtinguts amb altres resultats de simulacions estàndard de Dinàmica de Langevin i s'ha aplicat a situacions experimentals, com ara el temps de relaxació T2 dels protons en solucions aquoses de nanopartícules superparamagnètiques. Mencionar també que aquest model de simulació ha estat implementat i el corresponent programari s’ha posat a disposició de la comunitat científica de forma gratuïta, concebut com una eina de simulació que pot ser ampliada fàcilment per resoldre altres problemes d’interès. Per altra banda, també hem discutit diferents efectes que sorgeixen com a conseqüència de l’aplicació de camps magnètics inhomogenis a aquestes dispersions superparamagnètiques. En concret, hem estudiat el moviment de les partícules magnètiques disperses en fluids a través de camps magnètics inhomogenis, el que es coneix com magnetoforesi. Per a tal efecte, hem centrat els esforços en la descripció de la separació magnètica de col·loides mitjançant l’aplicació de gradients de camp magnètic uniformes, des de dispersions superparamagnètiques a mescles de col·loides amb diferent resposta magnètica. Hem validat aquests models teòrics comparant-los amb simulacions per ordinador i n’hem discutit la seva utilitat comparant-ne les prediccions amb resultats experimentals. L’anàlisi racional d'aquests resultats proporciona un marc idoni per a millorar el disseny i el rendiment de diferents separadors magnètics, així com plantejar noves estratègies de separació, com per exemple la separació cooperativa en dispersions superparamagnètiques. Existeixen, encara, problemes oberts que esperem que aquest treball ajudi a afrontar com, per exemple, entendre la interconnexió entre les estructures induïdes en dispersions superparamagnètiques i la seva dinàmica d’agregació. Aquest és un aspecte important en una gran varietat d'aplicacions industrials i de laboratori com són els processos de separació magnètica, tractament d’aigües residuals i eliminació de contaminants, immunoassaigs en aplicacions clíniques o la creació de nous materials supramoleculars. Tanmateix, esperem que els resultats que es presenten al llarg d'aquest document encoratgin nous estudis dins el camp de col·loides magnètics, ja sigui perfeccionant els resultats i mètodes aquí presentats o contribuint al desenvolupament de noves estratègies per afrontar problemes encara per resoldre.
Colloidal dispersions, a term coined by the Scottish scientist Thomas Graham in 1861, have been the subject of interest in different scientific areas during more than a century. A colloidal dispersion is characterized by the existence of a dispersed phase uniformly distributed throughout a dispersion medium. Many different compounds fall in this category like aerosols (smog, fog, clouds or dust), foams, emulsions (mayonnaise or milk) or gels (butter or jelly). Recent improvements in particle synthesis and colloidal stability have boosted the controlled design of new colloids on demand, targeting the required properties for each application. Among the large variety of different colloidal dispersions (either found in nature or man-made), we have studied a singular type of such dispersions where the colloids have a superparamagnetic behavior called superparamagnetic colloidal dispersions. In these dispersions, surprising features arise under the application of an external magnetic field, as a consequence of the interplay between characteristic colloidal interactions and the anisotropic magnetic dipole-dipole interaction between their constituent colloidal particles. Along this thesis we have used different theoretical and simulation methods to discuss a number of phenomena appearing in superparamagnetic colloidal dispersions. On the one hand, we have shown that the application of a uniform magnetic field to such dispersions may induce the reversible aggregation of superparamagnetic particles. In view of theoretical models and computer simulations, a new criterion based on the physical properties of the colloidal dispersion has been proposed to predict the formation of aggregates, and its validity has been discussed by comparing the predicted behavior with experimental results. We have provided evidences of the existence of an equilibrium state, where aggregate sizes acquire a steady distribution, an issue previously suggested but unclear up to now. We have also focused our attention on the growth kinetics of the aggregates and its implications in different phenomena observed in experiments. The need to reach the large time scales of some experiments has motivated the development of new models and simulation strategies to overcome the large time consuming calculations required in standard simulations. We have presented a new simulation model that provides a faster and reliable approach to address the formation of chain-like structures in superparamagnetic dispersions. The model has been validated by direct comparison with standard Langevin Dynamics simulations and has been applied to experimental situations like the T2 relaxation time of protons in aqueous solutions of superparamagnetic nanoparticles. Let us mention that the simulation model has been implemented and the corresponding computer code is free and available to the scientific community, envisaged as a new modeling tool readily extensible to other problems of interest. On the other hand, we have analyzed different effects arising as a consequence of the application of inhomogeneous magnetic fields to such superparamagnetic dispersions. Specifically, we have studied the controlled motion of magnetic particles dispersed in a liquid medium by using inhomogeneous magnetic fields, what is known as magnetophoresis. To do so, we have focused the efforts on the description of the magnetic separation of colloids by the application of uniform magnetic field gradients, from superparamagnetic dispersions to mixtures of colloids with different magnetic response. We have validated the theoretical models adopted against computer simulations and we have discussed their usefulness by comparing the predictions obtained with experimental results. The rational analysis of these results provides a proper starting framework to enhance the design and performance of different magnetic separators, as well as to shape new separation strategies, like the cooperative magnetophoretic separation in superparamagnetic dispersions. There exists, of course, open problems that we hope this work will help to deal with. For instance, a better understanding of the interplay between the induced structures in superparamagnetic dispersions and their aggregation kinetics. This is an important issue in a vast variety of industrial and lab applications as, for example, in magnetic separation-based processes, waste-water treatment and pollutant removal, immunoassays in clinical applications or in the assisted assembly of new supramolecular materials. Nevertheless, we hope that the results presented along this document could encourage further studies in magnetic colloids science, either refining the results and approaches provided here or developing new strategies to face unsolved problems.

In this project, self-assembly behaviour of colloidal particles was investigated by a combination of both computer simulations and experimental approach. In particular, a Brownian Dynamics algorithm was used to simulate either steep-repulsive spheres or spherocylinders in a shrinking spherical confinement. In accordance with literature, in the former case packed spheres were shown to crystallize into a distinctive icosahedral structure. In the latter study, spherocylinders clearly revealed a local tendency to form smectic layers. After the synthesis of micro-sized fluorescent-labelled silica spheres and rods, particle self-assembly in a spherical confinement was experimentally explored. While our selected method widely produced well-defined spherical supraparticles, it generally failed in inducing crystalline or liquid-crystalline ordering. This outcome was supposed to emerge due to fast compression of particles inside the confinement. In the last part of the project, Brownian Dynamics simulations of mixtures of rods and spheres in a spherical confinement were performed. Our preliminary investigation unveiled a modest tendency for rod-rich mixtures to form a binary smectic configuration. However, same-shape phase separation prominently occurred for increasing fractions of spheres. Notably, a quantitative analysis on the simulated configurations was accomplished by introduction of a novel binary smectic local order parameter.

In this thesis we have studied the influence of transport mechanisms on the adsorption kinetics of colloidal suspensions, as well as in the distribution of colloidal particles at the adsorbed layer. Adsorption of colloidal particles is controlled by the geometric exclusion effects at the surface originated by the finite size of the particles and by the irreversible character of the adsorption in these systems, and is also influenced by the specific transport mechanisms which control the arrival of the colloids from the bulk to the interface. Our main objective has been to elucidate the effects of each contribution, as well as their relative importance and mutual influence in some specific situations.

After a first chapter in which we have introduced the basic kinetic models which have been proposed in the literature to take into account surface exclusion effects (random sequential adsorption (RSA) and ballistic (BM) models), in the second chapter we have studied the adsorption in the presence of an external field parallel to the substrate. Our objective has been to elucidate how surface exclusion effects are sensitive to the imposed external conditions upon which adsorption takes place, showing that they do not arise from purely geometric constrains. Instead of carefully describing the transport process, we have conveniently modified the usual kinetic models. The basic feature now is that a new minimum length at which two particles can approach on the substrate appears, and the kinetics becomes asymmetric in the sense that this minimum distance depends on the side of the preadsorbed disk at which the incoming particle adsorbs. We have observed a decrease of the jamming limit with the strength of this imposed force, and also a tendency to form more locally ordered aggregates when this force increases. New adsorption mechanisms are induced by the external field: a particle may roll over a number of preadsorbed spheres before being either adsorbed or rejected, implying that adsorption becomes non-local in the sense that an incoming particle may interact with many preadsorbed disks. The pair distribution function exhibits a richer structure indicating that the clusters have internal structure since their relative separation is not univocally fixed. If the exclusion distance is a multiple of the diameter, then a resonance is observed when using BM rules, and a highly locally ordered substrate is formed.

In chapter 3 we have studied the effect of the transport on the adsorption of colloidal particles at high Peclet number in the presence of a gravity field, when their diffusion can be neglected. As a new mechanism with respect to previous studies, we have incorporated hydrodynamic interactions (HI) existing between the incoming particle and the adsorbed ones due to the fact that the particles are suspended in a fluid. We have shown that the basic effect of HI is to introduce an effective repulsive interaction between the incoming particle and the preadsorbed ones. Some analytic results obtained in very simplified conditions have helped us to understand the effects of HI, although un general, computer simulations have been carried out to study the adsorption process. We have seen that, although the global quantities obtained with HI do not differ quantitatively from the ones obtained for BM, as for example the coverage as a function of time, the jamming limit, or the available fraction of the line, the local structure differs significantly from the one obtained with BM. The pair correlation function is characterized by having a series of peaks due to the rolling of incoming spheres over preadsorbed ones. The behaviour behind the peaks is different, showing a slower decay with HI, indicating that because of the effective repulsion, larger gaps between the spheres are preferred, which implies that HI induce the formation of looser local structures on the substrate. We have shown that the effective repulsion introduced by HI favours the formation of elongated triplets on the surface where BM would predict more isotropic clusters, meaning that HI changes the structure of the clusters formed at the interface. We have compared with experimental results on the adsorption of mellamine particles. The curves obtained with HI agree better with the experimental ones than those obtained with BM, explaining therefore some of the discrepancies observed when comparing with BM. In particular, the slower decay behind the first peak can be thought of as being due to the effect of HI. This has served to show that BM, which was thought to be a good model to describe the adsorption of heavy colloidal particles, is restricted to situations where inertial effects dominate the transport to the wall.

Finally, in chapter 4 we have developed a thermodynamic theory for the adsorption process. We have focused our analysis on the situation in which adsorption is controlled by a surface energy barrier, which is more realistic for the adsorption of small particles. In this case, the transport to the interface is controlled by the diffusion through the energy barrier. In order to describe this process properly, we have introduced an additional internal variable for the fields at the surface in the thermodynamic description.

The surface exclusion effects at this level are introduced considering that the system at the surface is not ideal. In this way we have derived a local generalized Langmuir equation for the evolution of the surface concentration. If the adsorption is not controlled by an energy barrier, then the local thermodynamic description is different. We have shown how it is possible to obtain global generalized Langmuir equation which describes the evolution of the global surface concentration, using the fact that entropical barriers appear for the incoming particles. We have also studied the fluctuations around steady states in a systematic way. We have shown how to deduce the corresponding fluctuation-dissipation theorem when an internal degree of freedom is introduced, and we have applied the results to analyze the density correlation function of a simple adsorption model with diffusion.

Gradient diffusion coefficients of BSA were systematically determined up to much higher concentration than had been reported previously, which were found to be in accordance with the theoretical predictions based on the calculations of thermodynamic and hydrodynamic coefficients via different approaches. Dynamic light scattering experiments were also conducted with the commercially significantly protein, recombinant human lactoferrin, on which no gradient diffusion coefficients had been reported before. With the experimental results, a further development of the predictive method was made via applying the Watzlawek and Nägele's equation as well as the Zick and Homsy's data to the calculations of hydrodynamic coefficients. The refined model gives the greatly improved calculations of the gradient diffusion coefficients of lactoferrin. Experiments were extended from bio-colloids to inorganic colloids to more extensively test the model. Silica was chosen to carry out the measurements. Dilute limit calculations of gradient diffusion coefficients agreed well with the experiments. However, further work is required for the gradient diffusion model over a wide range of concentration studied. A theoretical analysis depending upon the calculations of thermodynamic and hydrodynamic coefficients has been applied. The thermodynamic coefficient was determined via (i) dilute limit calculations, (ii) solution of the Ornstein-Zernike equation or (iii) cell model calculations. Furthermore, the hydrodynamic coefficient was computed via (i) dilute limit calculations or (ii) a combination of perturbation theory and the results of an exact numerical solution for an ordered system. These coefficients were then combined, according to the generalized Stokes-Einstein equation, to allow comparison between theory and experiment.

The high quality CuxS nanocrystals were synthesized (Chapter 3) and the profound understanding and skills to prepare colloidal nanocrystals has been obtained and improved. It revealed a very simple synthetic route not only for the systematic investigation on the size control of the copper sulfide nanodisks but also for studying the influence of different stoichiometric ratios on the shape of copper sulfide nanocrystals. An increase of the precursor concentration in the growth solution resulted in the formation of tetradecahedral and dodecahedral nanocrystals. XRD results showed these nanodisks had a similar composition close to Cu1.78S as spherical nanocrystals, however, the tetradecahedral and dodecahedral nanocrystals were characterized with a composition close to Cu1.96S as deduced from their djurleite crystal phase. An oriented attachment was proposed as growth mechanism for polyhedrons growth and the slow nucleation rate allows an accurate control of the size and morphology of CuxS nanocrystals, from spheres and disks to tetradecahedrons and dodecahedrons by tuning the precursor concentration from 0.05 M to 1.0 M and reaction conditions. Dodecahedrons with different size can be easily prepared by elongating the reaction time. These nanocrystals can be used as cathodes in all-vanadium redox flow batteries and showed a significant improvement of the cathodic reaction reversibility, especially the dodecahedrons. The CuxSe nanocubes with mean edge length of 17 nm±0.9 nm were synthesized (Chapter 4). The role of various metal ions playing on shape of CuxSe nanocrystals was discussed during the synthesis. The underlying mechanism was illustrated by preparing copper selenide nanocubes in the presence of Al ions whereas there was no any Al detected on the surface or within the final cubes. The morphology control is proved to be thermodynamically directed during the ripening regime and it exemplified the shape-direction of semiconductor nanocrystals by metal ions for the first time. It is a platform to produce cubic nanoparticles with different composition by cation exchange such as Ag2Te nanocubes. The plasmonic properties of the obtained nanocubes were further characterized and it demonstrated the strong plasmonic absorption peak at 950 nm. A reproducible procedure to prepare highly monodisperse copper telluride nanocubes, nanoplates and nanorods was presented in Chapter 5. The procedure is based on the reaction of a copper salt with trioctylphosphine telluride (TOP-Te) in the presence of Lithium bis(trimethylsilyl) amide (LiN(SiMe3)2), trioctylphosphine (TOP), trioctylphosphine oxide (TOPO) and oleylamine (OLA). The high reaction temperature as 220 °C was found to be necessary to obtain cube-shaped NPs with narrow size distributions. By tuning the precursor ratio of Cu:Te, the size of these nanocubes could be controlled in the range between 10 and 20 nm. When decreasing the reaction temperature to 190 °C and the growth time to 15 min, highly homogeneous copper telluride nanoplates were produced. An increase of the TOP concentration from 0.125 ml to 0.75 ml resulted in the formation of nanorods. It was proposed the LiN(SiMe3)2 to activate the formation of a Cu-oleylamido complex and it is the actual species reacting with TOP-Te. The Cu-oleyamido complexes and/or lithium oleylamine may play a key role stabilizing the NP surface during growth. Copper telluride nanocubes and nanoplates display a strong near-infrared optical absorption at 900nm associated to localized surface plasmon resonances. This plasmon resonance can be exploited for the design of surface-enhanced Raman scattering (SERS) sensors for unconventional optical probes such as nile red containing oxygen based functional groups. This is the first time using Cu-chalcogenide as probes for SERS application and demonstrates its potential interest in future. Preliminary analysis of the use of copper telluride nanocubes as cytotoxic and photothermal agents is also discussed herein.
Inicialment vam establir les condicions per preparar Cu(x)S. Com a mecanisme de creixement es va proposar el que es coneix amb el nom d’oriented attachment, en el qual els nanocristalls s’uneixen en una determinada orientació per formar altres formes més complexes. Establint les condicions en les quals es donava aquest mecanisme podíem produir nanocristalls de Cu2-xS amb un acurat control sobre la seva composició i/o forma, des de partícules esfèriques fins a nanopartícules en forma de disc o bé acanat amb partícules amb forma tetradecaèdríca o dodecaèdríca. Aquest control es va aconseguir simplement variant la concentració del precursor i les condicions de reacció. El segon sistema que es va estudiar va ser la producció de nanocristalls de Cu(x)Se. En el nostre treball preteniem descobrir nous procediments per sintetitzar nanocristalls de Cu(x)Se controlant la seva morfologia. Es va descubrir que es podia controlar la forma final dels nanocristalls de Cu(x)Se simplement introduint ions metàl•lics a la solució. En particular, en presència d’ions d’alumini es van produir nanocubs amb una longitud lateral de 17 nm ± 0.9 nm. Addicionalment es van estudiar les propietats plasmòniques d’aquests nanocubs. També es van utilizar aquests cubs de seleniur de coure com a base per produir cubs d’altres semiconductors a travès de l’intercanvi catiònic. Com a exemple es van produir cubs de Ag(2)Te. Finalment, es va estudiar el calcogenur binari, Cu(x)Te. Es va desenvolupar un mètode de síntesi per produïr nanocubs, nanoplaques i nanorods altament monodispersos. Es va observar que els paràmetres clau per controlar la forma eren la temperatura i la quantitat de surfactants. En canvi, per controlar el tamany es va observar que el paràmetre més important era la proporció entre Cu i Te present a la solució. Aquests nanocristalls posseïen propietats plasmòniques amb un pic d’absorpció al voltant dels 900 nm.

The goal of this thesis is studying hydrodynamic effects on active colloidal suspensions. Hydrodynamic interaction is propagated through the fluid in which the colloids displace due to the flow they create during their motion. It can lead to the emergence of collective phenomena, such as the self-assembly of more complex structures. Hydrodynamic interactions are not the only present in the system, since other forces may be acting between colloids, or there can be external fields acting on them such as gravity. We present our study for two different systems: magnetic colloids and Janus particles. When applying a circular magnetic field, we can induce a rotation to a particle possessing a magnetic moment. Due to the coupling of the flow with the one created by surrounding particles and with system interfaces, a rotor will eventually self-propel. Two magnetic moments interact with each other through the magnetic dipole-dipole force, which tends to align them into arrays. We study how the balance between hydrodynamic, magnetic and gravitational forces determines the morphology of the structures magnetic colloids can form. Janus particles have two faces with different chemical properties, thus the interaction between them depends on their relative orientation. We study the morphology and order of the structures that can emerge for these particles as a function of the intensity, sign and reach of the interaction between them, as well as the type of flow they create when self-propelling. Methodologically, we have combined the use of far-field theory to draw analytical expressions that have given us qualitative insight on the results we could expect with high-performance computing simulations which have allowed us to extend our study to bigger systems.
En aquesta tesi ens proposem estudiar els efectes hidrodinàmics en suspensions col·loidals actives. La interacció hidrodinàmica es propaga a través del fluid en el que es desplacen els col·loids degut al flux que ells mateixos creen durant el seu moviment, podent donar lloc a l’emergència de fenòmens col·lectius, com l’autoorganització en estructures més complexes. Les interaccions hidrodinàmiques no són les úniques presents en el sistema, ja que pot haver-hi d’altres forces actuant entre els col·loids, o podem considerar l’efecte d’altres camps com la gravetat. Presentem el nostre estudi per a dos sistemes diferents: col·loids magnètics i partícules Janus. En aplicar un camp magnètic circular, es pot induir una rotació a una partícula que posseeixi un moment magnètic. Degut a l’acoplament del flux amb el creat per altres partícules i les parets del sistema, un rotor pot acabar desplaçant-se. Dos moments magnètics interactuen entre ells mitjançant la força dipolar, que afavoreix el seu alineament i la formació de cadenes de col·loids. Estudiem com el balanç entre interaccions hidrodinàmiques, magnètiques i efectes gravitatoris afecta a la morfologia de les estructures que poden formar els col·loids magnètics. Les partícules Janus tenen dues cares amb propietats químiques diferents, quelcom que dóna lloc a una interacció entre elles que depèn de la seva orientació relativa. Estudiem les estructures que poden aparèixer per a aquestes partícules com a funció de la intensitat, signe i abast d’aquesta interacció, així com de la forma del flux que creen en desplaçar-se. Metodològicament, hem combinat expressions analítiques aproximades per tenir una idea qualitativa dels fenòmens que hom pot esperar amb simulacions per ordinador per poder estudiar els fenòmens col·lectius en sistemes de més partícules.

The main objective of this thesis focuses on compositional design and engineering colloidal NPs and their application in energy conversion. This principally included the synthesis and characterization of colloidal NPs, and in-depth exploration of their catalytic properties. Special focus is the synthesis and characterization of copper-based chalcogenides, bimetallic and multicompent metal oxide NPs. The results were shown in the series of articles which have been published or are under review in high impact peer-review journals. These works can be extracted to conclusions as following: (1) Copper-based chalcogenides NPs: Detailed synthetic routes to produce CZTS and CZTS-based HNPs i.e. CZTS-Au, CZTS-Pt and CZTS-Ag2S. The composition, size and shape control of CZTS NCs have been achieved by tuning the precursor concentration, surfactants, gas bubbling and heating ramp. This synthetic strategy method can be easy to scale up to grams at the same time keeping above 90% yield per batch by a simple vacuum free heating-up method. We used CZTS NCs as electrocatalysts with controlled crystal phases for the ORR measurements. First-principles calculations and experiments both indicated the kesterite CZTS NCs exhibit improving electrocatalytic activities toward ORR. In additional, monodisperse CZTS-Au and CZTS-Pt HNPs were obtained base on CZTS as seeds by seed-mediated growth method. Various characterizations confirm the structure of noble-semiconductors HNPs. Such HNPs were investigated on photocatalytic degradation of dye and hydrogen evolution reaction in water, exhibited high catalytic active. The research of CZTS-based HNPs is extended to a detailed synthesis of CZTS-Ag2S HNPs involving cation exchange reaction. The structure and composition of CZTS-Ag2S could be tuned by control the ration of Ag precursors and CZTS seeds. When employing CZTS-Ag2S as sensitizers apply photoelectrochemical cell for water splitting, showed improved photocurrent response under visible-light illumination. (2) Bimetallic NPs: The synthesized Pd2Sn NPs were successfully used solution-based strategy. A mechanism of morphology structure was discussed detail based different ratio of OLA, chlorine and TOP precursors. When evaluating catalytic properties of geometry of Pd2Sn NPs, reduction of nitrophenol, water denitration and EOR were measured resulting in Pd2Sn NRs had outperformance catalytic active over Pd2Sn spherical NPs, while Pd2Sn alloy NPs exhibited better catalytic performance compare to Pd NPs. The formation of novel Au-Pd2Sn heterostructured NRs was described in detail as well. Au-Pd2Sn heterostructured NRs were synthesized via a seed-mediated growth method, which Au domains were selected to grow on the Pd2Sn seeds. The result establishes a new strategy for the development of multifunctional nanomaterials. (3) Multicompent metal oxide NPs: Mn3O4@CoMn2O4 core-shell and Mn3O4@CoMn2O4-CoO HNPs were prepared via partial cation exchange reaction via Mn3O4 seeds NPs and different cobalt precursors, which playing a crucial role whether additional nucleation of a CoO phase depending on the coordination ability of cobalt precursors. The lower coordination ability of cobalt perchlorate had a higher reactivity to grow CoO phase on Mn3O4@CoMn2O4 to form Mn3O4@CoMn2O4-CoO HNPs. In particular, such HNPs showed a superior catalytic activity and stability over the core shell catalysts and state-of-the-art electrocatalysts for ORR and OER in alkaline solution. Based on this colloidal synthetic route, Fe3O4@NixFe3-xO4 core shell NPs was obtained involving nickel perchlorate precursors to Fe3O4 seeds solution. The fabrication of this core shell NPs and ITO glass to form thin film as water oxidation catalyst exhibited an improved catalytic activity. This colloidal synthetic route offers an easy scale-up, low temperature and ambient pressure protocol to design earth-abundant, cost-effective and high activity water oxidation catalysts.
El objetivo principal de esta tesis se centra en el diseño de ingeniería de composición y NP coloidal y su aplicación en la conversión y almacenamiento de energía. Esto incluye principalmente la síntesis y caracterización de los NP coloidales, y la exploración a fondo de sus propiedades catalíticas. Se prestará especial atención es la síntesis y caracterización de calcogenuros a base de cobre, óxido de metal NP bimetálicas y multicompent. Estos trabajos se pueden extraer con el resumen de la siguiente manera: (1) calcogenuros base de cobre NP: basados ​​en CZTS rutas sintéticas detalladas para producir CZTS y heterostructured NP es decir CZTS-Au, Pt y CZTS-CZTS-Ag2S. La composición, el tamaño y la forma de control de CZTS CN se han conseguido mediante la regulación de la concentración de precursor, tensioactivos, burbujeo de gas y rampa de calentamiento. Utilizamos CZTS CN como electrocatalizadores con fases de cristal controlados para las mediciones de la reacción de reducción de oxígeno con cálculos y experimentos de primeros principios. En CZTS-Au adicionales, monodispersas, CZTS-PT y CZTS-Ag2S hetero-NP se obtuvieron sobre la base CZTS como semillas por el método de crecimiento de la semilla mediada. Tal Hetero-NP se investigaron sobre la degradación fotocatalítica de tinte, reacción de desprendimiento de hidrógeno en agua y celular fotoelectroquímico para la disociación del agua, exhibido alta catalítica activa. (2) bimetálica NP: Los Pd2Sn NP sintetizados se utilizan con éxito la estrategia basada en la solución. Un mecanismo de la estructura de la morfología se discutió detalle. Al evaluar las propiedades catalíticas de la geometría de Pd2Sn NP, la reducción de nitrofenol, desnitrificación del agua y la reacción de oxidación del etanol resultante se midieron en Pd2Sn NR había de resultados superiores activa catalítica sobre Pd2Sn esférica y Pd NP. La formación de la novela Au-Pd2Sn heterostructured NR se sintetizaron mediante un método de crecimiento de la semilla mediada, que fueron seleccionados Au dominios de crecer en las semillas de Pd2Sn. El resultado establece una nueva estrategia para el desarrollo de nanomateriales multifuncionales. (3) NP de óxido metálico Multicompent: Mn3O4@CoMn2O4 core-shell y Mn3O4@CoMn2O4-CoO hetero-NP se prepararon mediante la reacción de intercambio catiónico parcial a través de Mn3O4 semillas NP y diferentes precursores de cobalto. Tal Hetero-NP mostró una actividad catalítica y estabilidad superiores en los catalizadores de núcleo y corteza y electrocatalizadores el estado de la técnica para el oxígeno reacción de reducción / evolución en solución alcalina. En base a esta vía de síntesis coloidal, Fe3O4@NixFe3-xO4 de núcleo y corteza NP se obtuvo con precursores de perclorato de níquel a una solución semillas Fe3O4. La fabricación de este núcleo NP cáscara y el vidrio ITO para formar la película delgada como catalizador de oxidación en agua exhibe una actividad catalítica mejorada.

Le déplacement cohérent dirigé au sein de troupeaux, d’essaims, de nuées, prend place à toutes les échelles du vivant. En cherchant à rationaliser l’émergence de tels mouvements collectifs, les physiciens ont décrit ces assemblées comme des matériaux actifs. Ces matériaux sont formés de constituants auto-propulsés qui se déplacent spontanément dans une direction commune. Cette thèse expérimentale s’appuie sur la réalisation de troupeaux synthétiques pour explorer les propriétés de la matière active polaire dans des situations défavorables à son auto-organisation : leur dynamique en milieux désordonnés et leur réponse à des perturbations externes. Des rouleurs colloïdaux aux interactions d’alignement sont confinés au sein de dispositifs microfluidiques. Au-delà d’une densité seuil, ils forment un troupeau caractérisé par l’émergence d’un ordre en orientation de longue portée. Ces troupeaux colloïdaux font office de prototypes de la matière active polaire. Nous avons étudié la réponse d’un liquide actif polaire assemblé à partir de rouleurs colloïdaux. Nous avons montré que face à une perturbation longitudinale leur réponse est hystérétique. Nous avons expliqué théoriquement ce comportement non-linéaire et l’avons exploité pour réaliser des oscillateurs microfluidiques autonomes. Nous avons également étudié la dynamique de troupeaux colloïdaux qui se propagent dans des environnements hétérogènes. La présence d’obstacles distribués aléatoirement focalise les troupeaux le long de chemins privilégiés qui forment un réseau épars et tortueux. Augmenter le désordre conduit à la destruction du troupeau. Nous avons démontré que la suppression du mouvement collectif consiste en une transition discontinue, générique à tous les matériaux actifs polaires
Directed collected motion within herds, swarms and flocks, is a phenomenon that takes place at all scales in living systems. Physicists have rationalized the emergence of such collective behavior. They have described these systems as active materials. These materials are assembled from self-propelled units that spontaneously move in the same direction. By experimentally studying synthetic flocks, this work uncovers some properties of polar active materials in situations that disfavor their self-organization: their dynamics in disordered environments and their response to external perturbations. Colloidal rollers with alignment interactions are confined within microfluidic devices. At high density, they spontaneously form a flock which is characterized by the emergence of orientational long-ranged order. These colloidal flocks are prototypical realizations of polar active matter. We have studied the response of a polar active liquid assembled from colloidal rollers. We have shown that they display a hysteretic response to longitudinal perturbations. We have theoretically accounted for this non-linear behavior. We have used this behavior to realize autonomous microfluidic oscillators. We have also studied the dynamics of colloidal flocks that propagate through heterogeneous environments. Randomly positioned obstacles focalize flocks along favored channels that form a sparse and tortuous network. Increasing disorder leads to the destruction of flocks. We have demonstrated that the suppression of collective motion is a discontinuous transition generic to all polar active materials

This thesis focuses on different aspects of NCs colloidal synthesis, the exploration of the relevant surface chemistries that afford NC assembly and the NC implementation into porous nanomaterials. The work is divided into two blocks. The first block is devoted to developing and optimizing the synthesis of NCs followed by the examination of their suitability for potential applications in catalysis and photocatalysis. The second block is dedicated to establish procedures to fabricate single-component or multicomponent porous nanomaterials from NC building blocks. To embrace the use of the developed strategies in different application fields, several kind of materials were under research. Namely, metals (e.g. Au), metal oxides (e.g. CeO2, TiO2, Fe2O3), metal chalcogenides (e.g. In2S3, ZnS, PbS, CuGaS2 and Cu2ZnSnSe4), and their composites. CeO2 NCs synthesis was deeply investigated with the aim to achieve a proper control on the NCs morphology, facets exposed, crystal phase, composition, etc., required for application. Overall, CeO2 NCs with spherical, octapod-like branched, cubic hyperbranched, and kite-like morphology with sizes in the range 7 to 45 nm were produced by adjusting experimental conditions of the synthetic protocol. Branched and hyperbranched NCs showed higher surface areas, porosities and oxygen capacity storage values compared to quasi-spherical NCs. The NCs morphology-controlled synthesis has been extended to quaternary Cu2ZnSnSe4 (CZTSe). CZTSe NCs with narrow size distribution and controlled composition were produced. It was shown how off-stoichiometric CZTSe compositions were characterized by higher charge carrier concentrations and thus electrical conductivities. The strategy to functionalize the metal oxide NC surface composition by applying different ligands is proposed. This enables to develop a novel approach to assemble metal oxide NCs into porous gel and aerogel structures. Propylene oxide has been found to trigger the gelation process of glutamine functionalized NCs. The detailed investigation of the gelation mechanism is demonstrated for the case of ceria. The method is applied for NCs with different morphologies. Eventually, the versatility of the concept is proved by using of the proposed approach for the TiO2 and Fe2O3 nanocrystals. The assembly method has been extended to metal chalcogenides - In2S3 NCs - starting from the NCs synthesis, with further surface chemistry manipulation and eventually follows by the NC assembly into gels and aerogels. The optimization of NC surface chemistry was achieved by testing different ligand exchange approaches via applying short-chain organic and inorganic ligands. The assembly method based on ligand desorption from the NC surface and chalcogenide-chalcogenide bond formation has been established for In2S3. The comparison of the different ligands impact on the NC performance in colloidal form, when assembled into gels and when supported onto substrate is investigated towards photoelectrocatalysis. The oxidative ligand desorption assembly approach has been extended for multicomponent NCs for the case of CuGaS2 and CuGaS2-ZnS. Optimization of spin-coating process of the formed NCs inks followed by applying of sol-gel chemistry led to formation of highly porous layers from TGA-CuGaS2 and TGA-ZnS. Applied results of CuGaS2/ZnS nanocrystal-based bilayers and CuGaS2–ZnS nanocrystal-based composite layers have been shown by testing their photoelectrochemical energy conversion capabilities. The approach to adjust NC surface chemistry has been proposed and tested for performing multicomponent NC assemblies. Applying of different ligands for NC surface functionalization endows their surface with different charges which usually provides colloidal NCs stabilization. It has been found that mixing of oppositely charged NCs with certain concentration enabled their assembly/gelation via electrostatic interaction. The proposed approach has been applied and optimized to produce multicomponent NC gels and aerogels. The detailed investigation of the gelation mechanism is shown for combination of metal-metal oxide and metal oxide-metal chalcogenide NCs (Au-CeO2, CeO2-PbS). Applied results of the Au-CeO2 aerogels were demonstrated for CO-oxidation.
Esta tesis se centra en la síntesis coloidal de nanocristales (NCs), en la exploración de su química de superficie y en su ensabanado en nanomateriales porosos funcionales. Para demostrar la versatilidad de aplicación de dichas estructuras, en este estudio se han considerado NCs de distintos tipos de materiales: metales (Au), óxidos metálicos (CeO2, TiO2, Fe2O3), calcogenuros metálicos (In2S3, ZnS, PbS, CuGaS2,Cu2ZnSnSe4) y sus materiales compuestos. El trabajo se dividió en dos bloques. En el primero se desarrolló y optimizó la síntesis de NCs de óxidos y calcogenuros metálicos y se evaluó su potencial para aplicaciones de catálisis y fotocatálisis. Se investigó en profundidad la síntesis de NCs de CeO2, poniendo énfasis en controlar su morfología. Se consiguió producir NCs de CeO2 de forma controlada (esférica, octapodo ramificado, cúbico ramificado y romboidal) y con tamaño controlado (7-45 nm). Asimismo, se obtuvieron NCs de Cu2ZnSnSe4 con una fina distribución de tamaños y composición controlada. En el segundo bloque se establecieron y estudiaron procedimientos para fabricar nanomateriales porosos mono- o multicomponentes a partir del ensamblado de NCs. Se desarrolló una estrategia basada en el ajuste de la química de superficie de NCs de óxidos metálicos (CeO2, Fe2O3,TiO2) y de calcogenuros metálicos (In2S3, CuGaS2-ZnS) que permitió su ensamblaje controlado en estructuras porosas de tipo gel y aerogel. En el caso de los óxidos metálicos, se determinó que el ensamblado se inicia con la adición de un epóxido a NCs funcionalizados con glutamina, causando la gelación. La desorción oxidativa de ligandos basada en la formación de enlaces calcogenuro-calcogenuro se propuso como mecanismo de gelación en calcogenuros mono- (In2S3) y multicomponente (CuGaS2-ZnS). Se investigó el impacto del empleo de distintos ligandos en la eficiencia foto-electrocatalítica de NCs en forma coloidal, ensamblados en geles y soportados en sustratos. Se desarrolló y estudió el ajuste de la química de superficie de NCs para la obtención de ensamblajes multicomponente mediante interacción electrostática de coloides en suspensión. El mecanismo de gelación fue investigado al detalle para materiales compuestos de NCs de oxido metálico (CeO2) con NCs de óxido de calcogenuro (PbS-CeO2) y metálicos (Au-CeO2). Los aerogeles de Au-CeO2 demostraron potencial para la oxidación de CO.

Los polímeros de coordinación y su diseño racional permiten la formación de materiales nanoestructurados con una amplia variedad de propiedades. Las múltiples combinaciones entre iones metálicos y ligandos orgánicos como precursores de materiales autoensamblados, han fascinado a los científicos durante décadas. La aplicación de la química de coordinación a nanoescala se considera uno de los enfoques más versátiles para el desarrollo de nuevos materiales nanoestructurados debido a las infinitas posibilidades para alcanzar propiedades sin precedentes. Además, el desarrollo de sistemas metal-orgánicos ha despertado en una gran cantidad de ejemplos para su uso en una amplia gama de aplicaciones. En esta Tesis hemos estado particularmente interesados ​​en el ajuste controlado de las propiedades de los materiales nanoestructurados basados ​​en polímeros de coordinación que se obtuvieron a través de diferentes rutas sintéticas. El método de síntesis, la selección adecuada de precursores y el estudio de las propiedades finales han centrado el trabajo realizado. Además, la formación de suspensiones coloidales estables en agua se estableció como un requisito principal para su potencial aplicación. Para eso, fue necesaria una sinergia multidisciplinaria con el objetivo de buscar la aplicación final de los nuevos materiales nanoestructurados desarrollados. El logro de este objetivo fue posible gracias a un diseño adecuado de la estrategia seguida junto con la caracterización completa de las nanoestructuras preparadas. En una primera parte de esta Tesis, la nanoestructuración de sistemas conmutables basados ​​en Fe(II) con comportamiento de entrecruzamiento de espín (SCO por sus siglas en inglés) se logró siguiendo dos estrategias diferentes. Por un lado, se aplicó una metodología descendente (top-down) basada en la exfoliación en fase líquida para el aislamiento de láminas 2D de cristales multilaminares. Por otro lado, a través de un enfoque ascendente (bottom-up), la síntesis de nuevas nanopartículas fue posible modulando la difusión de la reacción utilizando metodologías basadas en microfluidica. En ambos casos, los materiales nanoestructurados se integraron en matrices poliméricas para evaluar su aplicación potencial como películas termocrómicas para su prueba de concepto. En la segunda parte de la Tesis, se estableció una nueva familia de polímeros de coordinación a nanoescala (NCP por sus siglas en inglés) basados ​​en Fe(III), Gd(III), Mn(II), In(III) y Cu(II) a través de su síntesis racional usando una reacción en un sola etapa. Las nanopartículas obtenidas se validaron mediante pruebas preclínicas in vivo que muestran un rendimiento interesante como posibles agentes teranósticos para la obtención de imágenes (resonancia magnética, tomografía por emisión de positrones y tomografía computarizada por emisión de fotón único) y pretratamiento potencial de glioblastoma y enfermedades pulmonares.
Coordination polymers and its rational design let the formation of nanostructured materials with a broad variety of properties. The multiple combinations between metal ions and organic ligands as precursors of self-assembled materials have fascinated scientists for decades. The application of coordination chemistry at the nanoscale is considered one of the most versatile approaches for the development of new nanostructured materials due to the infinite possibilities for reaching unprecedented properties. Furthermore, the development of metal-organic systems has aroused in a plethora of examples for their use in a wide range of applications. In this Thesis we have been particularly interested in the fine tune of the properties of nanostructured materials based on coordination polymers whose were obtained through different synthetic routes. The method of synthesis, the properly selection of precursors and the study of the final properties has centred the work carried out. Additionally, the formation of water-stable colloidal suspensions was stablished as a main requirement for their potential application. For that, a multidisciplinary synergy was necessary with the aim to pursue the final application of the novel nanostructured materials developed. Achieving this objective was possible thanks to a properly design of the strategy followed together with complete characterization of the nanostructures prepared. In a first part of this Thesis, the nanostructuration of Fe(II)-based switchable systems with spin crossover behaviour was achieved by following two different strategies. On the one hand, a top-down methodology based on liquid-phase exfoliation was applied for the isolation of 2D flakes from the bulk crystal. On the other hand, through a bottom-up approach, the synthesis of novel nanoparticles was possible by modulating the reaction diffusion using microfluidic based methodologies. In both cases, the nanostructured materials were integrated in polymeric matrices to evaluate their potential application as proof-of-concept thermochromic films. In the second part of the Thesis, a novel family of nanoscale coordination polymers (NCPs) based on Fe(III), Gd(III), Mn(II), In(III) and Cu(II) was stablished through its rational synthesis by using one-pot reaction. The nanoparticles obtained were validated by pre-clinical in vivo tests showing interesting performance as potential theranostic agents for imaging (Magnetic resonance imaging, positron emission tomography and single-photon emission computed tomography) and potential pre-treatment of glioblastoma and lung diseases.

The role of pseudopathogenic microorganisms (PPM) in infectious diseases is growing. In Ukraine, like in the world, from year to year increases the incidence of acute intestinal infections (AII). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/32192

In the present thesis I have worked with particle dispersion in water as well as in liquid crystal. As the first study of this thesis, I have studied the aggregation of isotropic (spherical) and elongated anisometric (pear-shaped) colloidal particles in aqueous medium, confined in two dimensions when subjected to perpendicular external alternating current (AC) electric fields. For low frequencies (f < 2.5kHz) the electrohydrodynamic flow is predominant, and particles tend to aggregate in clusters. On the contrary, for higher frequencies the repulsive dipolar interaction dominates, and particles disperse. Although both types of particles feature a similar behavior under AC field, pear-shaped particles present a richer phase diagram, that is, they have more phases than the spherical ones. I have also found that pear-shaped particles tend to form smaller and more elongated aggregates, with faster aggregation kinetics. I have also tested different ways to measure the strength of the colloidal aggregates using magnetic probes. The following studies of this thesis focus on colloidal dispersions in liquid crystals, which are widely used nowadays to clarify new fundamental concepts and original applications.(1–5) Nematic liquid crystals (NLC) are anisotropic organic fluids whose molecules exhibit the positional disorder of a liquid, but are aligned in a certain direction (called the director of the NLC) (6,7). The director field is usually controlled by certain boundary conditions imposed on the plates of the experimental cell. As a novel way to determine the director orientation, I have demonstrated that paramagnetic anisometric inclusions can be used to locally control the in-plane orientation of the director field by means of external weak magnetic fields. To better understand the phenomenon I have also developed a theoretical model based on the free energy density of the NLC. Additionally, I have found that, by rotating the paramagnetic inclusions more than 100º from their initial orientation, a target pattern of dark and light alternated circles appear. This phenomenon is also captured by the model proposed. In the third phase of this project, I have investigated the controlled motion of micrometer inclusions dispersed in a nematic liquid crystal, propelled by an alternating current (AC) electric field. Recently it has been reported in the literature that micrometric particles can be propelled in NLC by using AC fields, provided that these particles break the symmetry of the NLC director around them. The mechanism explaining this propulsion is called Liquid Crystal-Enabled Electrophoresis (LCEEP) (3). By taking advantage of this mechanism, I have demonstrated that aqueous microdroplets are also propelled by LCEEP. One can make these droplets transport solid polystyrene microparticles, or perform a chemical reaction by coalescing two microdroplets containing separate reactants. In addition, I have also demonstrated the control of the activation or deactivation of LCEEP by using photosensitive particles, which change the NLC director symmetry around them upon UV-visible irradiation. In the last part of this thesis I have developed a novel technique to separately control particle driving from steering under LCEEP. Using photo-induced patterns, I assemble and dynamically control ensembles of particles in a NLC medium. These swarms are assembled, transported and dynamically addressed by local irradiation of the photosensitive cell plate with UV light. With this technique I have demonstrated different potential applications: from the formation and reconfiguration of lattices composed of particle swarms, to segregation of particles with different sizes, as well as the storage and subsequent release of a swarm inside physical constraints, or the formation of particle jets. All these phenomena unveil novel possibilities in the field of collective transport of driven inclusions. References: (1) Koenig, G. M.; Lin, I.-H.; Abbott, N. L. Chemoresponsive Assemblies of Microparticles at Liquid Crystalline Interfaces. Proc. Natl. Acad. Sci. 2010, 107, 3998–4003. (2) Lintuvuori, J. S.; Stratford, K.; Cates, M. E.; Marenduzzo, D. Colloids in Cholesterics: Size-Dependent Defects and Non-Stokesian Microrheology. Phys. Rev. Lett. 2010, 105, 178302. (3) Lavrentovich, O. D.; Lazo, I.; Pishnyak, O. P. Nonlinear Electrophoresis of Dielectric and Metal Spheres in a Nematic Liquid Crystal. Nature 2010, 467, 947–950. (4) Pishnyak, O. P.; Tang, S.; Kelly, J. R.; Shiyanovskii, S.; Lavrentovich, O. D. Levitation, Lift, and Bidirectional Motion of Colloidal Particles in an Electrically Driven Nematic Liquid Crystal. Phys. Rev. Lett. 2007, 99, 127802. (5) Tasinkevych, M.; Mondiot, F.; Mondain-Monval, O.; Loudet, J.-C. Dispersions of Ellipsoidal Particles in a Nematic Liquid Crystal. Soft Matter 2014, 10, 2047–2058. (6) Oswald, P.; Pieranski, P. Nematic and Cholesteric Liquid Crystals: Concepts and Physical Properties Illustrated by Experiments; Taylor& Francis: Boca Raton, 2005. (7) Kleman, M.; Lavrentovich, O. D. Soft Matter Physics - An Introduction; Springer, 2003.
Durant aquesta tesi, he treballat amb dispersions de partícules en l'aigua, així com també amb dispersions en cristall líquid nemàtic (NLC). Com a primer estudi d'aquesta tesi, he investigat la influència de camps elèctrics en dispersions col·loïdals de partícules sòlides en un medi aquós. He estudiat l'agregació de partícules col·loïdals isotròpiques (esfèriques) i anisomètriques allargades (amb forma de pera) en un medi aquós confinat en dues dimensions, quan se sotmet a un camp elèctric de corrent alterna (AC) perpendicular a la superfície de confinament. En un segon estudi he demostrat que es poden utilitzar inclusions anisomètriques paramagnètiques per controlar localment l'orientació d’un NLC, per mitjà de camps magnètics febles. Per entendre millor el fenomen també he desenvolupat un model teòric basat en la densitat d'energia lliure del NLC. A més, he estat capaç de generar patrons complexos, que també s’expliquen amb model proposat. En la tercera fase d'aquest projecte, he investigat el moviment controlat d'inclusions micromètriques disperses en NLC, impulsades per un corrent altern (AC) a traves d’un mecanisme anomenat “electroforesi habilitada per cristall líquid” (LCEEP). He demostrat que microgotes aquoses es poden propulsar per LCEEP. Es pot fer que aquestes microgotes transportin micropartícules sòlides de poliestirè, o dur a terme una reacció química mitjançant la coalescència de dos microgotes que contenen reactius separats. A més, també he demostrat el control de l'activació o desactivació de la LCEEP mitjançant l'ús de partícules fotosensibles, en funció de la irradiació UV-visible. En l'última part d’aquesta tesi he desenvolupat una nova tècnica per a controlar separadament la propulsió i la direcció de moviment de les partícules transportades per LCEEP. Mitjançant l’ús de patrons fotoinduïts, es poden formar i controlar dinàmicament conjunts de partícules en un medi de NLC. Aquests eixams es formen, es transporten i es dirigeixen dinàmicament per irradiació local amb llum UV. Amb aquesta tècnica he pogut demostrat diferents aplicacions potencials: des de la formació i reconfiguració de xarxes cristal·lines compostes d'eixams de partícules, a la segregació de partícules de diferents mides, així com l'emmagatzematge i posterior alliberament d'un eixam dins d’un canal micromètric, o la formació de jets de partícules. Tots aquests fenòmens revelen noves possibilitats en el camp del transport col·lectiu d'inclusions propulsades.

The utilization of membrane treatment for the production of potable water has become more prevalent in today's industry. As drinking water regulations become more stringent this trend is expected to continue. Widespread use is also a result of membrane treatment being the best available treatment in many cases. While membrane treatment is a proven technology that can produce a consistently superior product to conventional treatment methods, membrane fouling and concentrate disposal are issues that drive up the cost of membrane treatment and can effectively eliminate it from consideration as a treatment alternative. This research focused on membrane fouling. A series of filtration experiments were conducted on various membranes to investigate the physical and chemical factors that influence fouling. The effects of both organic and colloidal fouling were explored by conducting research on various commercial membranes and experimental membranes by Saehan Industries, Inc. (Saehan). Saehan's membranes were in various stages of development in their process of creating a more fouling resistant membrane (FRM). Various hydrodynamic and chemical conditions were used to characterize the evolution of the Saehan commercial products to the experimental FRMs. The developmental stage of the membrane tested included analysis of the various trade secret coating techniques termed single, double, and special. A proprietary post-treatment process was also utilized in combination with each of the coating techniques. The developmental membranes were also compared to commercially available FRMs. The existing FRMs showed better fouling resistance than Saehan's commercially available products in high organic surficial groundwater testing. Synthetic colloidal water testing demonstrated the superior performance of the FRMs, but was not acute enough to differentiate the fouling performance within the group of FRMs or Saehan products. Average roughness decreased slightly as coating technique progressed from single to double to special. Post-treatment increased roughness in single coated membranes and reduced the roughness in double and special coated membranes. The relative charge differences in the developmental membranes were exhibited among non post-treated membranes. Post-treatment membranes did not demonstrate relative surface charge differences consistent with the manufacturer. Initial mass transfer coefficient, determined by clean water testing, increased as coating moved from single to double to special. Clean water testing showed increased initial mass transfer coefficient for membranes with post-treatment. Single coated membranes showed the best salt rejection capability among non post-treated membranes. Post-treatment increased selectivity for all membrane coating techniques. The coating effect on fouling potential had an inverse relationship between single coated versus double and special coated membranes. The post-treatment increased fouling resistance for the single coated membranes, but decreased fouling resistance of double and special coated membranes. The SN7 membranes showed the best performance of the developmental membranes.
M.S.Env.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering

La fabricación ascendente de nanoestructuras supramoleculares definidas es clave para el desarrollo de nuevos materiales funcionales basados en sistemas autoensamblados. En este marco, los liposomas son algunos de los nanoobjetos autoensamblados más estudiados desde su descubrimiento fortuito en 1964. Estos sistemas se describen como vesículas, formadas por fosfolípidos, compuestas de una o más bicapas lipídicas concéntricas que rodean compartimentos acuosos. Los liposomas están ampliamente reconocidos como portadores farmacéuticos debido a su biocompatibilidad, biodegradabilidad y baja toxicidad. Actualmente estas nanoestructuras se utilizan en uso clínico para una variedad de indicaciones contra el cáncer, enfermedades inflamatorias y dermatológicas, y en diversos tipos de vacunas. A pesar de su versatilidad y biocompatibilidad, el traslado a uso clínico de formulaciones liposomales está obstaculizado por la tendencia a agregación que tienen estos sistemas lipídicos autoensamblados y por su bajo grado de homogeneidad estructural, atributos críticos de calidad con un alto impacto en las propiedades farmacológicas. Los liposomas corresponden a estados metaestables cinéticamente atrapados, que se forman por el aporte de energía externa a una fase lamelar plana (por ejemplo, sonicación o filtración mecánica). La estabilidad de estas estructuras está cinéticamente limitada debido a que sus componentes lipídicos son muy insolubles, y por lo tanto, las fase lamelar plana colapsada es el estado de equilibrio de la agregación. Además, los liposomas sufren alteraciones químicas y físicas, que acortan su vida útil y limitan, como consecuencia, la estabilidad y las condiciones de almacenamiento de los fármacos. Debido a estas condiciones especiales de preparación y almacenamiento, junto con el elevado precio de los fosfolípidos, existe un gran interés en la búsqueda de nuevos componentes que se autoensamblen en vesículas estables y que cumplan los estándares de calidad requeridos en formulaciones farmacéuticas. El uso de surfactantes, como moléculas sustitutas más económicas y más estables que los fosfolípidos, ha surgido como una opción muy interesante para la producción industrial de los sistemas vesiculares en aplicaciones farmacéuticas y cosméticas. Además, se ha demostrado que el uso de colesterol en muchas formulaciones vesiculares, ayuda a modular la fluidez de la bicapa, reducir las fugas y mejorar la eficiencia de encapsulación (EE) de los fármacos. Por lo tanto, en la búsqueda de nuevas formulaciones de vesículas estables no liposomales, es muy interesante la formación de vesículas basadas en colesterol. En este marco, el grupo Nanomol descubrió la formación de unas nuevas nanovesículas utilizando mezclas acuosas de colesterol y bromuro de hexadeciltrimetilamonio (CTAB), un surfactante catiónico. Esta formación vesicular se logró mediante una tecnología basada en fluidos comprimidos, el método DELOS-SUSP. Es importante destacar que ninguno de los componentes individuales que forman estas nuevas nanovesículas se autoensamblan para formar estructuras vesiculares, ya que en agua los esteroles insolubles forman cristales y los surfactantes de amonio cuaternario forman micelas. En vista de la alta estabilidad que estas vesículas supramoleculares basadas en colesterol mostraron, esta Tesis se ha dedicado al estudio profundo del fenómeno de autoensamblaje y del comportamiento de fases relacionado con estas nuevas nanoestructuras. Hemos reportado la capacidad de surfactantes iónicos y colesterol para autoensamblarse conjuntamente formando en medios acuosos bicapas cerradas, que hemos nombrado quatsomes. Hemos investigado estas nanovesículas no liposomales a diferentes niveles, desde su formación hasta sus aplicaciones. Además, hemos estudiado la formación de otras estructuras supramoleculares basadas en colesterol, con morfología no vesicular, por el proceso DELOS-SUSP. Por lo tanto, esta Tesis contribuye a mejorar el conocimiento de las organizaciones supramoleculares basadas en colesterol y demuestra el enorme potencial de las metodologías basadas en fluidos comprimidos para la producción de nanoestructuras coloidales autoensambladas estables con un alto contenido de colesterol.
The bottom-up fabrication of defined supramolecular nanostructures is key to the development of novel functional materials based on self-assembling systems. In this regard, liposomes are among the most studied self-assembled nanoobjects since their serendipitous discovery in 1964. They are defined as phospholipid vesicles consisting of one or more concentric lipid bilayers surrounding aqueous compartments. Liposomes are well recognized as pharmaceutical carriers because of their biocompatibility, biodegradability and low toxicity. They constitute one of the most successfully translated delivery systems that are currently in clinical use for a variety of indications against cancer, inflammatory and dermatological diseases, and in various types of vaccines. Despite their versatility and biocompatibility, the translation to the clinic of liposomal formulations could be hindered by the tendency of these lipid self-assemblies to aggregate and by their low degree of structural homogeneity, which are critical quality attributes with a major impact on the pharmacological properties. Liposomes correspond to metastable kinetically trapped states, which are formed by the input of external energy on a planar lamellar phase (e.g., sonication or mechanical filtration). The stability of these structures is kinetically limited because their lipid building blocks are highly insoluble, and therefore, the collapsed planar lamellar is the equilibrium state of aggregation. Additionally, liposomes suffer chemical and physical alterations, which shorten their shelf-life and limit, as a consequence, drug stability and conditions of storage. Due to these special conditions of preparation and storage together with the elevated price of phospholipids, there is a great interest in finding nonphospholipid building blocks or tectons, which self-assemble into stable vesicles and which satisfy the quality standards required in pharmaceutical formulations. The use of surfactants as cheaper and more stable substitutive molecules than phospholipids has emerged as a really interesting choice for the industrial production of vesicular systems in pharmaceutical and cosmetic applications. Besides, it has been proved that the use of cholesterol in many vesicle formulations helps to modulate the bilayer fluidity, to reduce the leakage, and to enhance the encapsulation efficiency (EE) of drugs. Therefore in the finding of stable non-liposomal vesicle-like assemblies, it is considerably interesting the formation of cholesterol-based supramolecular vesicles. Within this framework, Nanomol group discovered the formation of novel stable non-liposomal nanovesicles using aqueous mixtures of cholesterol and hexadecyltrimethylammonium bromide (CTAB), a cationic surfactant. This vesicle formation was achieved by a compressed fluid (CF)-based technology, the DELOS-SUSP method. It is noteworthy that none of the individual components of these novel nanovesicles self-assemble to form vesicular structures, since in water the insoluble sterol species form crystals and quaternary ammonium surfactants form micelles. In view of the high stability that these cholesterol-based supramolecular vesicles exhibited, this Thesis has been devoted to deep study the self-assembling phenomena and phase behavior related to these new nanostructures. We have reported on the ability of ionic surfactants and cholesterol to self-assemble forming stable amphiphilic building-blocks with the appropriate structural characteristics to form, in aqueous phases, closed bilayers, which we named quatsomes. We have investigated these novel non-liposomal nanovesicles at different levels, from their formation up to their applications. Furthermore, we have also studied the formation of other cholesterol-based supramolecular assemblies with non-vesicular morphology by the DELOS-SUSP process. This Thesis therefore contributes to improve the knowledge about cholesterol-based supramolecular assemblies and demonstrates the enormous potential of CF-based methodologies for the production of stable self-assembled colloidal nanostructures with high content of cholesterol.

Our main goal is to study certain aspects of the dynamics of fluids with magnetic particles in suspension, based on their promising practical applications as new materials as welI as on its fundamental scientific interest. In the introduction we brief the reader on the most essential properties of the system. We have characterized the monodomain magnetic particles and the time scales inherent to magnetic fluids. Having introduced the rotational diffusion equation as the most convenient tool to take into account the different mechanism inftuencing the dynamics of the particles, we have also proposed a fruitful approach for solving it in any general situation. We have also highlighted the macroscopic properties of the magnetic fluid treated now as a continuous medium and showed up the different phenomena associated with the lack of stability in the system. In Chapter I we concentrate on two limit cases whose analysis is easier but very illustrative. The first part of the chapter is devoted to the study of a suspension of rigid dipoles, in which the magnetic moments are rigidly attached to the body of the particles themselves. In these conditions, if we apply an external magnetic field both the magnetic moment and the particle move together so that the magnetic torque acting upon it becomes zero. Thermal fluctuations tends to disrupt this order, and it turns out that, for instance, that the effective viscosity of the suspension depends on the dimensionless parameter comparing magnetic and thermal energies. In the second part we consider magnetic materials with finite anisotropy energy at high magnetic fields. For such monodomain particles the magnetic moments rapidly orient along the direction of the external field, and then as a second step the mechanical rotation of the particles takes place. In this case, the effective viscosity of the suspension is a function of the magnetic anisotropy constant of the material, of the volume of the particles as well as the thermal energy. Our results are compared to experimental measurements. The second chapter is concerned with the determination of the viscosity and of some magnetic and optical properties of magnetic fluids in the whole range of possible experimental situations. The magnetic moments and the particles inside the liquid reorient separately but their dynamics are coupled thus giving rise to a more intricate relaxation process. We have compared part of our results with available experimental data for different ferrofluids showing quite a good agreement. In Chapter III we joint to our discussion of magnetic fluids the presence of nonmagnetic particles of micrometer size and study their motion through the ferrofluid. The ferrofluid is considered now as a continuous medium with new transport coefficients already determined in the previous sections. Under the action of a rotating external magnetic field, we study the rotational motion of the nonmagnetic particles and compare our expressions to sorne measurements carried out in these composite systems. In this chapter we are also con cerned with the characterization of the hydrodynamic interactions among these particles in a carrier ferrofluid. Chapter IV is intended as a brief introduction to the multiple problems which arise when one handle the aggregation phenomena which may take place in these systerns. We study the kinetics of the forrnation of the aggregates by rneans of the Smoluchowski theory of coagulation in colloids. But we account for hydrodynarnic interactions which are not usually considered when studying such process and that gives rise to sorne corrections for high concentrations of particles. In addition, the rheology of the chains that are usually observed in systerns with dipolar interactions is given for a rather simplified situation in order to elucidate the effects of the dipolar magnetic interactions. Finally, we sum up our main conclusions and indicate some of the perspectives stimulated by the contents of this monograph and in which we plan to pursue work in the near future.
A lo largo de esta monografía nos hemos ocupado del estudio de sistemas fluidos, tanto con monodominios magnéticos como con dos tipos distintos de partículas, magnéticas y no magnéticas, en dispersión en un líquido newtoniano en situaciones fuera del equilibrio. El comportamiento de estos sistemas se ve influenciado en gran medida por la presencia de un campo magnético externo, lo que da lugar a nuevos fenómenos que han sido el fundamento de muchas aplicaciones prácticas. Sin embargo, esta influencia depende de los diferentes procesos de relajación que tienen lugar dentro las partículas, con respecto a sus ejes cristalinos, así como fuera de ellas, con respecto al fluido portador. Hemos descrito cuáles son estos procesos y obtenido la dependencia con respecto de los parámetros que describen las partículas y el fluido, de algunos coeficientes que caracterizan las propiedades reológicas, magnéticas y ópticas de la suspensión coloidal.

Metal phosphides are an important class of functional materials that exhibit a wide range of applications for energy storage and conversion. However, the synthesis of metal phosphide nanoparticles and its scalability is often limited by the toxicity, air sensitivity and high cost of reagents used. In this thesis, a simple, scalable and cost-effective procedure was developed to produce metal phosphides using inexpensive, low-toxicity and air-stable triphenyl phosphite as phosphorus source. The use of chlorides or metal carbonyl as metal precursors and hexadecylamine as ligand allowed the synthesis of a variety of phosphide nanocrystals (NCs) including phosphides of Ni, Co, Cu, Fe, Mo. The use of NiCl2 and CoCl2 mixture as metal precursors, ternary metal phosphide Ni2-xCoxP (0≤x≤2) NCs could be obtained. The synthesis of Ni2-xCoxP involved the nucleation of amorphous Ni-P and its posterior crystallization and simultaneous incorporation of Co. Tuning the experimental parameters allows producing NCs with different composition, morphology and particle size. Ni2-xCoxP-based electrocatalysts exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction compared to binary phosphides. In particular, NiCoP electrocatalysts displayed very low overpotential of 97 mV at J = 10 mA cm-2 and an excellent long-term stability. Density functional theory (DFT) calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NCs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2-xCoxP series. The use of chromium hexacarbonyl as metal precursor and high boiling point oleylamine as ligand, less-studied CrP NCs could also be produced. This method allows producing CrP with nanometric particle size and with a very high throughput and material yield. CrP NCs were mixed with carbon to prepare electrocatalysts, which exhibited remarkable activity and stability toward oxygen reduction reaction in an alkaline electrolyte and an absolute tolerance to methanol. DFT calculations demonstrated CrP to provide a very strong chemisorption of O2 which facilitates its reduction and explains the excellent performance. Besides, another phosphorus source hexamethylphosphorous triamide (HMPT) and new synthetic strategies were applied for the synthesis of SnP and PdP2 NCs. SnP NCs were produced from the reaction of HMPT and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in sodium-ion batteries, which displayed a high reversible capacity of 600 mA h g-1 at a current density of 100 mA g-1 and cycling stability for over 200 cycles. The excellent cycling performance was associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. The synthesis of PdP2 involves the reaction of palladium acetylacetonate and HMPT to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorus incorporation, crystallize into PdP2. The produced PdP2 NCs showed high mass activity and long-term stability toward the ethanol oxidation reaction in alkaline media. The activity and stability of the PdP2-based catalyst were further improved by supporting PdP2 NCs onto reduced graphene oxide (rGO). PdP2/rGO catalysts showed high current densities up to 51.4 mA cm-2 and mass activities of 1.60 A mg-1Pd, that is 4.8 and 15 times higher than Pd NCs. Overall, in this thesis serval metal phosphide nanomaterials were produced by colloidal synthetic strategy, and showed highly performance for electrochemical energy conversion and storage applications.
Los fosfuros metálicos son materiales funcionales de gran interés e impacto en la sociedad debido a su gran rendimiento en almacenamiento y conversión de energía. Sin embargo, la síntesis de nanopartículas de fosfuros metálicos y su escalabilidad es limitada. En la presente tesis, se ha desarrollado un proceso de producción para nanopartículas de fosfuros metálicos simple, escalable y rentable. El éxito de los resultados radica en el uso de fosfito de trifenilo, considerado como una fuente de fósforo barata, estable al contacto con el aire y no tóxica, que además permite la síntesis de una gran variedad de nanocristales (NCs) (fosfuros de Ni, Co, Cu, Fe, Mo, así como fosfuros ternarios de Ni2-xCoxP). Optimizando los parámetros experimentales, es posible producir NCs de diferente composición, morfología y tamaño. Además, el uso de solventes de alto punto de ebullición, facilita la síntesis de materiales menos estudiados como el CrP. Los NCs de Ni2-xCoxP y CrP NCs pueden ser combinados con carbono dando lugar a electrocatalizadores útiles para reacciones tales como evolución de hidrógeno y reducción de oxígeno, respectivamente. El uso de otras fuentes de fósforo, como por ejemplo la triamida de hexametilfósforo, permite a su vez producir NCs de SnP y PdP2. En el caso particular de SnP, los NCs demostraton poseer una geometría esférica y una fase cristalográfica trigonal con una superestructura atribuida a los pares difósforos ordenados. Mezclados con carbón negro y utilizados como ánodos en baterías de ion sodio, estos NCs demostraron una alta capacidad reversible de 600 mA h g-1 a una densidad de corriente de 100 mA g-1 y estables durante más de 200 ciclos. Por otro lado, los NCs de PdP2 soportados sobre óxido de grafeno se utilizaron como electrocatalizadores para la oxidación de etanol, mostrando una alta densidad de corriente de hasta 51.4 mA cm-2 y una actividad de masa de 1.60 A mg-1Pd. En resumen, se han desarrollado métodos de síntesis basados en estrategias coloidales para poder producir una gran variedad de fosfuros metálicos a escala nanométrica, mostrando estos un gran rendimiento para su uso en conversión y almacenamiento de energía electroquímica.

The work developed during this PhD has embraced several topics that I divide in three blocks. Each block contains two chapters in this dissertation. Additionally, a general introduction of the different topics is provided (Chapter 1). The first block corresponds to the study of colloidal synthetic routes to produce functional nanoparticles (Chapter 2 and 3). In the second block the developed nanoparticles are used to produce bulk nanostructured materials. The functional properties of the nanomaterials are also characterized in this second block. As the paradigmatic application for such bottom-up assembled nanostructured materials I considered thermoelectricity (Chapter 4 and 5). In the last block, I go one step beyond and design and prepare multiphase nanoparticles as building blocks for the bottom up production of nanocomposites with improved thermoelectric performance (Chapter 6 and 7).
El treball desenvolupat durant aquesta tesi doctoral engloba diverses temàtiques que s’han dividit en tres blocs. Cada bloc conté dos capítols. A més a més, com a Capítol 1 s’ha inclòs una introducció general de cadascuna de les temàtiques tractades. En el primer bloc, Capítols 2 i 3, s’estudien diferents síntesis col·loïdals per produir nanopartícules funcionals. En el segon bloc, Capítols 4 i 5, les nanopartícules desenvolupades s'utilitzen per produir materials nanoestructurats en bulk a partir del seu assemblatge. Les propietats funcionals d’aquests nanomaterials es caracteritzen també en aquest segon bloc. Com a aplicació paradigmàtica s’ha considerat la termoelectricitat. En l'últim bloc, Capítols 6 i 7, es va un pas més enllà i es dissenyen nanopartícules heterogènies com blocs de construcció per a la producció de nanocompostos amb millor rendiment termoelèctic.

In this project, nanoparticles were produced by solution-based one-pot synthesis, particularly colloidal methods. A series of powerful tools were used to characterize the structure and surface compositions before they were tested as anode materials in the field of energy conversion and storage. Firstly, we produced colloidal Ni polyhedral (16 ± 2 nm) and spherical (13 nm) NCs. The electrocatalytic properties of electrodes based on these NCs were first investigated in variable concentrations of KOH. Electrodes based on Ni polyhedral NCs displayed impressive current densities (59.4 mA cm 2) and mass activities (2016 mA mg 1) at 0.6 V vs. Hg/HgO in the presence of 1.0 M methanol and 1.0 M KOH, which corresponds to a twofold increase over electrodes based on spherical Ni NCs and over most previous Ni-based electrocatalyts previously reported. Electrodes based on faceted polyhedral NCs displayed a 30% loss of activity during the first few operation hours, but activity stabilized to around a 65% of the initial value after ca. 20000 s operations. And also, we developed a new synthetic route to produce NiSn intermetallic NPs with composition control. Detailed electrochemical measurements showed that these NPs exhibited excellent performance for MOR in alkaline solution. Ni-rich NiSn-based electrocatalysts displayed slightly improved performances over Ni-based electrocatalysts. Most notorious was the significantly improved stability of NiSn catalysts compared with that of Ni. This work represented a significant advance in developing cost-effective electrocatalysts with high activity and stability for MOR in DMFCs. In another sub-section of the energy conversion, a series of Ni3 xCoxSn2 (0 ≤ x ≤ 3) NPs were produced based one the protocol. A preliminary optimized catalyst composition, Ni2.5Co0.5Sn2, showed a current density of 65.5 mA cm 2 and a mass current density of 1050 mA mg 1 at 0.6 V vs. Hg/HgO for the MOR in 1.0 M KOH containing 1.0 M methanol. While the introduction of Co slightly decreased the durability with respect to Ni3Sn2, Ni2.5Co0.5Sn2 NP-based electrodes demonstrated significant stability during continuous cycling and increased activity at high methanol concentrations. The presence of Sn was found to be essential to improve stability with respect to elemental Ni, although Sn was observed to slowly dissolve in the presence of KOH. In the energy storage field, we focused on the performance as anode material in LIBs and SIBs. Among the different NixSn compositions tested, best performances toward Li+ ion and Na+ ion insertion were obtained for Ni0.9Sn NP-based electrodes. This optimized cycling charge-discharge performance for LIBs provided 980 mAh g 1 at 0.2 A g 1 after 340 cycles. Additionally, Ni0.9Sn NP-based electrodes were tested in Na+-ion half cells, exhibiting 160 mAh g 1 over 120 cycles at 0.1 A g 1. The pseudocapacitive charge-storage accounted for a high portion of the whole energy storage capacity, which was associated to the small size and the composition of the NixSn NPs used. In the last chapter of the project, the CoxSn NP composition was adjusted over the range 1.3 ≤ x ≤ 0.3. These Co-Sn solid solutions were tested as anode materials in LIBs on a half-cell battery system. Among the different compositions tested, Co0.9Sn and Co0.7Sn NPs provided the best performance, with a charge-discharge capacity above 1500 mAh g 1 at a current density of 0.2 A g 1 after 220 cycles and up to 800 mAh g 1 at 1.0 A g 1 after 400 cycles. Through the kinetic analysis of Co0.9Sn NPs by the CV measurement, we found these charge-discharge capacities to include a very large pseudocapacitive contribution, up to 81% at a sweep rate of 1 mV s 1, which we related to the small size of the particles.

El YBa2Cu3O7-δ es el superconductor de alta temperatura con mayor potencial tecnológico para aplicaciones de potencia e imanes que trabajan bajo campos magnéticos elevados. Sin embargo, todavía es un reto mejorar sus prestaciones en forma de película delgada epitaxial con un coste bajo de fabricación. La deposición de soluciones químicas ha surgido como una técnica muy competitiva para obtener láminas delgadas epitaxiales y multicapas de alta calidad con nanoestructuras controladas. Hemos desarrollado un proceso novedoso de crecimiento mediante Calentamiento Flash que muestra un excelente potencial para la producción industrial en continuo de conductores epitaxiales de YBa2Cu3O7-δ. En esta tesis hemos establecido, por primera vez, una imagen completa que describe las fases intermedias y la evolución de la microestructura durante el calentamiento. Hemos extendido la ventana de la temperatura de crecimiento sin ninguna degradación de las propiedades superconductoras, por lo que la deposición de conductores epitaxiales de YBa2Cu3O7-δ es compatible con el uso de sustratos de cinta metálica con capas tampón de CeO2. Además, también hemos encontrado que este proceso de crecimiento promueve la formación de una alta concentración de defectos de apilamiento y, por lo tanto, de tensiones a escala nanométrica. Las láminas ultrafinas de YBa2Cu3O7-δ y nanocompuestos, en el rango de 5-50 nm, se prepararon después de una optimización de los parámetros de crecimiento. La reducción de la energía interfacial induce una alta densidad de defectos de apilamiento, lo que conduce a una matriz de YBa2Cu3O7-δ altamente distorsionada. Esta modificación microestructural se vuelve extremadamente grave cuando el grosor de la lámina delgada disminuye por debajo de 25 nm, degradando significativamente las propiedades superconductoras. También hemos estudiado la evolución de las características de las nanopartículas segregadas espontáneamente con el espesor de las láminas delgadas y su influencia en la eficiencia del anclaje de vórtices. La preparación de nanocompuestos de YBa2Cu3O7-δ a partir de nanopartículas de óxido preformadas y no reactivas que forman soluciones coloidales ha demostrado ser una estrategia muy exitosa para lograr un estricto control de las características de las nanopartículas y la optimización de la nanoestructura de las láminas delgadas superconductoras. Las perovskitas BaMO3 (M = Zr, Hf) son las composiciones más prometedoras de nanopartículas preformadas que hasta ahora han conducido a láminas delgadas de nanocompuestos de alta calidad con altas concentraciones de nanopartículas (20-25% molar). La composición y el tamaño de las nanopartículas han demostrado ser factores cruciales para adaptar el rendimiento del anclaje de vórtices bajo campos magnéticos aplicados. La aplicación del proceso de crecimiento de calentamiento flash al crecimiento de láminas delgadas nanocompuestas permite la preservación del tamaño de las nanopartículas y la generación de una alta densidad de defectos de apilamiento de pequeña longitud, que desempeñan un efecto sinérgico para aumentar la eficiencia de los centros de anclaje de vórtices artificiales y mejorar así las propiedades de los conductores. La técnica de multideposición es efectiva para aumentar aún más el espesor de la lámina delgada, mientras que la eficacia del anclaje de vórtices se conserva y la capacidad de transporte de corriente eléctrica de las láminas delgadas nanocompuestas aumenta.
YBa2Cu3O7-δ (YBCO) is the best material choice to address the performances required in power applications and magnets working under high magnetic fields. However, it is still challenging to achieve low manufacturing costs and high superconducting performances of coated conductors (CCs) for large scale power applications. Chemical Solution Deposition has emerged as a very competitive technique to obtain epitaxial films and multi-layers of high quality with controlled nanostructures. We have developed a novel Flash Heating growth process that shows high potential to be compatible with the industrial reel-to-reel production of YBCO CCs. Here we have set up, for the first time, a full image describing the intermediate phase and microstructure evolution during this heating process. We extend the growth temperature window down to 750 ºC without any degradation of superconducting properties, making it being compatible with the deposition of YBCO CCs on CeO2-caped metallic tape substrates. In addition, we have also found that this growth process promotes the formation of a high concentration of stacking faults and so of nanostrain. YBCO and nanocomposite ultrathin films, in the range of 5-50 nm, have been prepared after a series optimization of growth parameters. The relief of the interfacial energy induces a high density of stacking faults, leading to a highly distorted YBCO matrix. Such microstructural disorder becomes extremely serious when the film thicknesses decrease below 25 nm, significantly degrading the superconductivity. We have also studied the evolution of the characteristics of spontaneous segregated nanoparticles with nanocomposite film thicknesses and their influence on the vortex pinning efficiency. The preparation of YBCO nanocomposites from non-reactive preformed oxide nanoparticles forming colloidal solutions has demonstrated to be a very successful strategy to achieve a tight control of the nanoparticle characteristics and the optimized nanostructural landscape on the superconducting films. BaMO3 (M=Zr, Hf) perovskites are shown to be the most promising compositions of preformed nanoparticles up to now that led to high quality nanocomposite films at high nanoparticle concentrations (20-25 mol%). The composition and size of nanoparticles have demonstrated to be crucial factors for tailoring vortex pinning performance in applied magnetic field. The application of the Flash Heating growth process in the growth of nanocomposite films allows both the preservation of nanoparticle size and the generation of a high density of short stacking faults, which play a synergistic effect to increase the artificial pinning centers and enhance the strong pinning contribution. Multi-deposition technique is proved effective to further enhance the film thickness while vortex pinning efficiency is preserved and current-carrying capacity of the nanocomposite films is increased.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.
Includes bibliographical references (p. 245-255).
This study investigates the thermal transport behavior of nanoparticle colloids or nanofluids. The major efforts are: to determine methods to characterize a nanoparticle colloid's mass loading, chemical constituents, particle size, and pH; to determine temperature and loading dependent viscosity and thermal conductivity; to determine convective heat transfer coefficient and viscous pressure losses in an isothermal and heated horizontal tube; and finally to determine the feasibility for potential use as enhanced coolants in energy transport systems, with focus on nuclear application. The efforts result in proving that the two selected nanofluids, alumina in water and zirconia in water, have behavior that can be predicted by existing single phase convective heat transfer coefficient and viscous pressure loss correlations from the literature. The main consideration is that these models must use the measured mixture thermophysical properties. With the acquired knowledge of the experiments, investigation into the potential use or optimization of a nanofluid as an enhanced coolant is further explored. The ultimate goal of contributing to the understanding of the mechanisms of nanoparticle colloid behavior, as well as, to broaden the experimental database of these new heat transfer media is fulfilled.
by Wesley Charles Williams.
Ph.D.

La present tesis va consistir en el disseny de nous nanocatalitzadors de cobalt per a la reacció de Fischer-Tropsh (FT). Les nano partícules de Cobalt van ser sintetitzades utilitzant diferents metodologies: reducció química utilitzant borohidrur de sodi com agent reductor o, descomposició tèrmica de compostos organometàl·lics tals com Co2(CO)8. Les síntesis van ser realitzades en presència de polímers com agents estabilitzants. Després de la síntesis, les nano partícules de cobalt foren aïllades, caracteritzades (utilitzant TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA i RAMAN) i provades en la reacció de Fischer-Tropsch en fase aquosa. Amb la finalitat de comparar amb catalitzadors suportats clàssics, les nano partícules de cobalt van ser immobilitzades amb TiO2 i provades en FT utilitzant un reactor de llit fix. En aquest estudi es va observar que l'activitat i la selectivitat de les nanopartícules de cobalt en ambdós sistemes catalítics depenien altament de paràmetres tals com el mètode de síntesis, el polímer estabilitzant i la mida de partícula. Aquestes diferències van ser atribuïdes a variacions en l'estructura i composició de les nano partícules que alhora eren intrínseques de cada paràmetre d'estudi.
La presente tesis consistió en el diseño de nuevos nanocatalizadores de cobalto para la reacción de Fischer-Tropsch (FT). Nanoparticulas de cobalto fueron sintetizadas usando diferentes metodologías: reducción química usando borohidruro de sodio como agente reductor o descomposición térmica of compuestos organometálicos tales como Co2(CO)8. Las síntesis fueron realizadas en presencia de polímeros como agentes estabilizantes. Después de la síntesis, las nanopartículas de cobalto fueron aisladas, caracterizadas (usando TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA and RAMAN) y probadas en la reacción de Fischer-Tropsch en fase acuosa. Con la finalidad de comparar con catalizadores soportados clásicos, las nanopartículas de cobalto fueron también inmovilizadas en TiO2 y probadas en FT usando reactores de lecho fijo. En este estudio se observó que el desempeño (actividad y selectividad) de las nanopartículas de cobalto en ambos sistemas catalíticos dependió altamente de parámetros tales como el método de síntesis, el polímero estabilizante y el tamaño de partícula. Estas diferencias fueron atribuidas a variaciones en la estructura y composición of las nanopartículas que a su vez eran intrínsecas a cada parámetro de estudio
The present thesis consisted in the design of novel cobalt nanocatalysts for the Fishcer-Tropsch (FT) synthesis. Cobalt nanoparticles were synthesized using different methodologies: chemical reduction method using sodium borohydride as reducing agent or thermal decomposition of organometallic precursors such as Co2(CO)8. The syntheses were carried out under the presence of polymer stabilizers. After the synthesis, the cobalt nanoparticles were isolated, characterized (using TEM, HR-TEM, XRD, XPS, ICP, FTIR, TGA and RAMAN) and tested in the Aqueous Phase Fischer-Tropsch synthesis. For comparison purposes with classical supported catalysts, the cobalt nanoparticles were also immobilized on TiO2 and tested in FT using fixed bed reactors. In this study was observed that the catalytic performance (activity and selectivity) of the cobalt nanoparticles in both catalytic systems were highly dependent on parameters such as the synthetic methodology, the polymer stabilizer and the particle size. These differences were attributed to variations in the structure and composition of the NPs intrinsic to each parameter under study.

In this thesis we investigate the structure formation and the out-of-equilibrium dynamics of driven and active magnetic colloids. The interactions in our system were tuned in situ by using external fields, with the aim of finding novel approaches to drive and engineer these microparticles into a rich variety of microstructures. The colloids formed chains and clusters able to transport cargos, space-filling gels and self-healing crystals. Moreover, we demonstrated the bidirectional transport of paramagnetic particles on top of a structured magnetic substrate. Because of their associated length-scale, colloids are experimentally accessible with traditional optical microscope techniques. We analysed the data extracted from digital video microscopy and used such information to infer the particle dynamics. Colloids have been proven to be excellent model systems for structures across different length scales that are more difficult to observe, such as collections of atoms and molecules. Furthermore, they are helpful test-beds to investigate fluid dynamics at low Reynolds number and can form artificial micromachines that are essential for the realization of disparate functional tasks at the microscale.
En aquesta tesi hem investigat la dinàmica fora de l'equilibri de col·loides magnètics i el seu comportament individual i col·lectiu. Controlant les interaccions utilitzant camps magnètics externs i l'activitat química de col·loides especialment sintetitzats, vam construir microdispositius nedadors capaços de transportar altres materials i formar cadenes, agrupacions, gels, i cristalls amb l'habilitat de reordenar-se. A més, vam demostrar el transport bidireccional de partícules paramagnètiques sobre un substrat magnètic. A causa de la seva mida, els col·loides són fàcilment accessibles experimentalment i es poden observar amb microscopis òptics tradicionals. Mitjançant tècniques de videomicroscopia, vam obtenir informació sobre la dinàmica fora d'equilibri dels sistemes estudiats. S'ha demostrat que els col·loides poden ser sistemes model excel·lents per estructures amb diferents escales de longitud que són més difícils d’observar. D'altra banda, els col·loides ens van ajudar a comprendre la dinàmica de fluids a baix nombre de Reynolds, el que té aplicacions en estudis de microfluídica. Aquest treball és un pas més que ens acosta a trobar un microdispositiu òptim basat en partícules col·loïdals per manipular, transportar i controlar processos a aquestes escales.

Particles dispersed in nematic liquid crystals (NLCs), also called nematic colloids, are nowadays typical experimental systems studied in the field of Soft Matter. In this scenario, the interactions and forces between colloidal particles are in equilibrium, and thus, elasticity governs inter-particle interactions. Furthermore, the application of an AC electric external field leads to a totally different scenario where the system is out-of-equilibrium, and thus, new physical phenomena can emerge. Nematic colloidal particles can be propelled under the application of an electric field, which allows for driven particles scenarios. Briefly, motion of colloids arises from the appearance of electroosmotic flows surrounding the particles. The symmetry breaking of these flows at particles apexes induces net propulsion to the particles. In this dissertation, we show that the transport modes of a single particle propelled in a NLC are different for the motion parallel and perpendicular to the averaged molecular orientation of the material, the director field. Here, the observed trends do not depend on the driving mechanism neither the propulsion speed. While motion is ballistic in the driving direction (parallel to the nematic director), our experiments show that transversal fluctuations can become superdiffusive depending on the configuration of the NLC surrounding the particle. For the superdiffusive behaviour, which is related to dipolar configurations of the nematic director, we have proposed a mechanism based on the geometry of the liquid crystal backflow to justify the persistence of thermal fluctuations affecting on the orientation of the dipolar configuration, and thus, the observed superdiffusive modes. Going further, and by using hundreds of anisometric particles, we have induced colloidal clusters assembled above a topological defect. By tuning the elastic properties of the NLC material by in situ modification of the anchoring conditions, two different configurations can be induced, aster or rotating mills. This process is achieved thanks to a photosensitive surface which allows to switch from the trans (homeotropic) to the cis (planar) isomer (NLC) under UV-light irradiation. In the case of asters, we observe the formation of stationary clusters that display radially extended density gradients with three different states of aggregation, an innermost “jammed” part, followed by a liquid-like corona and ending in a diluted, gas-like, phase. Moreover, we can describe our system with a non-equilibrium equation of state and directly determine the effective pressure and temperature in the system. In contrast, for the rotating mills we obtained a dynamic assembly that has been analysed in terms of velocities and order parameters. To understand either the different assemblies obtained or the phases observed, we developed a theoretical model that combines different interactions resulting from phoretic propulsion, dipolar forces and hydrodynamics allowing to capture the basic physics of the process. The last part of this thesis is based on steering and guiding the collective colloidal transport by means of both photo-patterning and confining devices. The first set of experiments of experiments is based on understanding the dynamics of an ensemble of flocking particles dispersed in a NLC. Furthermore, we show the implementation of obstacles for the flock to pass. To conclude, this work not only increases our fundamental knowledge of micron-sized particles dispersed in anisotropic materials, such as nematic liquid crystals, but it serves as a starting platform to explore the motion of driven colloids inside them. Special emphasis will be put on the implementation of new techniques for guiding and steering the colloidal trajectories by means of both photo-patterning and microfluidic devices, as it has been demonstrated to be key towards the control of colloidal trajectories.
Les partícules dispersades en un cristall líquid nemàtic (CLN), també anomenats col·loides nemàtics, són avui dia sistemes experimentals estudiats en el camp de la “Soft Matter”. En aquest escenari, les interaccions i forces entre partícules col·loïdals es troben en equilibri, així, l’elasticitat governa les interaccions entre partícules. Més enllà, l’aplicació d’un camp elèctric altern dóna lloc a un escenari totalment diferent, on el sistema es troba fora d’equilibri, i així, nous conceptes físics poden sorgir. Els col·loides nemàtics es poden propulsar sota l’acció d’un camp elèctric, el qual permet escenaris on els col·loides són dirigits. Breument, el moviment de les partícules és degut a l’aparició de fluxos electroosmòtics al voltant de les partícules. El trencament de la simetria dels fluxos a banda i banda de la partícula indueix una propulsió neta. En aquest manuscrit es mostra des de l’estudi del transport d’una partícula individual en termes de modes de transport fins a l’estudi de moviments col·loïdals col·lectius. L’estudi d’una partícula individual s’ha dut a terme sota l’acció de dos mecanismes diferents de propulsió, el de sedimentació-difusió i la “Liquid Crystal-Enabled Electrokinetics”. Per altra banda, prenent avantatge de la última hem pogut auto-assemblar centenars de partícules formant clústers amb una distribució radial inhomogènia de la densitat de partícules. Per entendre aquest tipus de clústers hem desenvolupat un model teòric i el Dr. Arthur Straube ha realitzat simulacions que concorden tant qualitativa, com quantitativament amb les tendències experimentals. Finalment, hem estudiat el fet de traslladar un eixam de partícules, però també el fet de posar-li obstacles per on hagi de passar. Per concloure, aquest treball no només augmenta el coneixement general de partícules micro- mètriques dispersades en CLNs, però serveix com a eina per iniciar-se i explorar el moviment dirigit de col·loides dispersat en aquests.

In the first part of this thesis, we study the kinetics of the complexation of a double-stranded DNA byNCp7 protein. To do this, we study the evolution of mechanical properties of DNA and its complexation by stretching the DNA/NCp7 complex with a optical trap. We observed that the persistence length of the complex decreases progressively during the complexation. Using astatistical model we describe the evolution of the flexibility of DNA complexed with NCp7. Our main result is that the fraction phi of base pairs that have reacted is not a linear function of time at low phi.We interpret our results assuming that the adsorption of NCp7 on DNA is highly cooperative. In the second chapter, we describe the dynamics of probe particles in a colloidal glassy suspension of Laponite. Laponite is a colloidal discoidal particle of 25 nm in diameter and 0.92 nm thick. We take advantage of evanescent wave microscopy, and follow the movement of fluorescent latex particles.Then we image these particles. We show that for a movement that has a single characteristic time scale, it is simply a linear function of time. We find that, what ever their size, the motion of probe particles can be described by a succession of two dynamic modes, where the fastest mode corresponds to the diffusion of particles in a viscoelastic fluid.

Living organisms and systems are continually converting energy, either internally stored or transduced from their surroundings, into motion. This activity and the resulting self-propulsion constantly push these biological systems out of thermal equilibrium. A number of exotic phenomenon result from the intrinsic non-equilibrium nature of these living systems, that are not accessible in a system at thermal equilibrium. In recent years, these ubiquitous non-equilibrium systems have come to be classified as active matter. Active matter, by definition, refers to systems composed of active units, each capable of converting ambient or stored energy into systematic movement. Examples range from the sub-micrometer scale, with microtubules associated with motor proteins in the cytoplasm, to the micrometer length scales of swimming bacteria, and the meter-length scales of greater familiarity, such as that of fish and birds. There are two common themes that run through all these active matter systems. The first is the emergence of correlated collective phenomenon through particle-particle interactions as exemplified in flocking of birds, swarming of bacteria and crystallization of self-propelled particles. And the second is the ability of the active units to interact with their surroundings through self-propulsion. Common examples of this include chemotaxis and rheotaxis, observed in many biological systems. In this thesis, I have focussed on studying the ability of artificial active matter systems to respond to their local environment. As a model active matter system, we use colloidal active particles, that propel due to self-diffusiophoresis. These particles coated with two different materials on each half are referred to as Janus particles. In a solution of H2O2, one of the sides has catalytic properties (Pt), while the other half remains inert (SiO2). This creates a concentration gradient of the reaction product along the surface of the particle and induces a phoretic slip, which propels the particle. We study the dynamics of these self-phoretic particles close to solid surfaces. The particles interact with their surroundings via hydrodynamic and phoretic effects and we observe that when confined closed to a surface, a strong alignment interaction comes into play. This effect can be used to guide micron sized active particles along predetermined pathways. We then exploit this alignment interaction to design micropatterned ratchets capable of generating a strong directional flow of active particles. A different geometry of the same system can also be used to accumulate active particles in confined areas. Finally, we study the influence of an applied external shear flow on the dynamics of active particles near surfaces. We find that a strong directional response emerges for the active particles in the direction perpendicular to the flow direction leading to the cross-stream migration of active particles. This response is dependent on the applied shear flow and the propulsion velocity of the particle, potentially opening up a possibility to sort particles of different activities based on their response to shear flows. Overall, our results indicate that active particles can have a strong directional response in certain environments allowing us to engineer ways of guiding them.
Los organismos y sistemas vivos convierten energía almacenada internamente o derivada de sus alrededores en movimiento de forma continua. Esta actividad puede causar una constante auto-propulsión que lleva a estos sistemas a un estado fuera de equilibrio térmico. Gracias a esto, aparecen un gran número de fenómenos exóticos que no son accesibles para un sistema que se encuentra en equilibrio térmico. En los últimos años se ha clasificado a estos sistemas de no equilibro como “material activa”. La materia activa, por definición, incluye los sistemas compuestos de unidades activas, cada una de ellas capaz de convertir la energía almacenada o del entorno en movimiento sistemático. Existen varios ejemplos que van desde la escala sub-micrométrica, donde podemos encontrar a los microtúbulos asociados a proteínas motoras en el citoplasma, a las grandes escalas, donde se encuentran sistemas más familiares como peces o pájaros, pasando por la escala micrométrica, donde nadan las bacterias. Podemos diferenciar dos temas principales que se manifiestan en todos estos sistemas de materia activa. El primero es la aparición de fenómenos colectivos correlacionados a través de interacciones partícula-partícula, como ocurre en bandadas de pájaros, enjambres bacterianos y la cristalización de partículas auto-propulsadas. El segundo es la capacidad de estas unidades activas de interaccionar con sus alrededores a través del fenómeno de la auto-propulsión, por ejemplo, a través de quimiotaxia o reotaxia, como se puede observar en muchos sistemas biológicos y que ya han sido reportados en varios estudios. En esta tesis, me he enfocado en el estudio de este último tema principal: la interacción de partículas activas con su entorno local. Como modelo de sistema de materia activa, usamos partículas activas coloidales que se propulsan gracias al fenómeno de auto-difusioforesis. Estas partículas están recubiertas por dos materiales diferentes en cada una de sus caras, y son comúnmente llamadas “partículas Janus”. Una de sus caras está recubierta con Pt, material que cataliza la descomposición de H2O2, mientras que la otra cara está recubierta de un material inerte (SiO2). En una solución de H2O2, la reacción que ocurre en la parte catalítica produce un gradiente de concentración de producto a lo largo de la superficie de la partícula e induce un deslizamiento forético que la propulsa. En esta tesis se ha estudiado la dinámica de estas partículas "autoforéticas" cerca de superficies sólidas. De manera natural, las partículas interaccionan con su alrededor debido a los efectos foréticos e hidrodinámicos. Cuando estas partículas se hayan confinadas cerca de una superficie, observamos que se origina en ellas una fuerte interacción de alineamiento. A partir de ello, consideramos interesante diseñar ratchets micro estampados capaces de generar un flujo direccional de partículas activas. Por otra parte, estudiamos la influencia de aplicar un flujo de cizalla externo en la dinámica de las partículas activas cerca de superficies. A consecuencia del flujo externo, encontramos que en el sistema emerge una respuesta fuertemente direccional para las partículas activas en la dirección perpendicular al flujo provocando una migración "cross-stream" de partículas activas.

L’estudi de nanopartícules és una branca fascinant de la ciència. Les seves propietats fortament relacionades amb la seva mida ofereixen innombrables oportunitats per descobriments sorprenents. Tanmateix, el mateix comportament sense precedents que proporciona a aquests nanomaterials el seu gran potencial per a aplicacions tecnològiques innovadores, també planteja grans reptes als científics. Alguns d'aquests reptes són el diseny de síntesis altament controlables i reproduïbles i el desenvolupament d’eines de caracterització i protocols de manipulació precisos que poden diferir dels d’altres materials més convencionals. L'objectiu d'aquesta tesi és proporcionar un marc per al disseny, la síntesi, la caracterització i la modificació superficial de nanopartícules col·loïdals d'or i plata. La tesi consta de diferents capítols que s'ordenen seguint una seqüència lògica que comença per la síntesi de les nanopartícules amb control de grandària, seguida de la caracterització de les seves propietats òptiques i catalítiques, i finalment l'exposició d’aquestes a medis biològics.
Nanoparticle research is a fascinating branch of science. The strongly size-related properties of nanoparticles offer innumerable opportunities for surprising discoveries. However, the same unprecedented behaviour that endows these nanomaterials with their great potential for innovative technological applications, also poses great challenges for scientists. Some of these challenges are the design of highly controllable and reproducible syntheses and the development of precise characterization tools and handling protocols that may differ from those of conventional materials. The aim of this dissertation is to provide a framework for the design, synthesis, characterization and surface modification of colloidal noble metal nanoparticles, with special focus on gold and silver nanoparticles. The thesis consists on different chapters that are ordered following a logic sequence that starts by the aqueous synthesis of gold and silver nanoparticles, followed by the characterization of their size-dependent optical and catalytic properties, and finally the exposure of the nanoparticles to biological media.

Els metamaterials són materials artificialment estructurats, minuciosament dissenyats per a l’obtenció de propietats electromagnètiques no observables en la natura, com l’índex de refracció negatiu. L’objectiu d’aquesta tesi és el desenvolupament de metamaterials òptics a gran escala que puguin ser fàcilment incorporats en dispositius reals. Combinant la litografia col·loïdal i el electrodeposició, vam presentar un disseny bottom-up de metamaterials tipus fishnet fets de capes d’or i aire. L’adequat disseny experimental i teòric dóna lloc a índexs de refracció fàcilment variables en l’infraroig proper. Aquesta estructura és duta a metamaterials tipus fishnet multicapes fets a partir de litografia per nanoimpressió i electrodeposició. Analitzem en detall la resposta òptica de les estructures, que donen lloc a grans índexs negatius des del visible fins a l’infraroig. Estudiem la seva aplicació com a sensors òptics infiltrant diferents líquids en les cavitats d’aire. Aquestes tècniques són igualment utilitzades per al desenvolupament de plataformes metàl·liques nanoestructurades per a l’observació de l’emissió espontània col·lectiva.
Los metamateriales son materiales artificialmente estructurados, minuciosamente diseñados para la obtención de propiedades electromagnéticas no observables en la naturaleza, como el índice de refracción negativo. El objetivo de esta tesis es el desarrollo de metamateriales ópticos a gran escala que puedan ser fácilmente incorporados en dispositivos reales. Combinando la litografía coloidal y el electrodepósito, presentamos un diseño bottom-up de metamateriales tipo fishnet hechos de capas de oro y aire. El adecuado diseño experimental y teórico da lugar a índices de refracción fácilmente variables en el infrarrojo cercano. Esta estructura es llevada a metamateriales tipo fishnet multicapas hechos a partir de litografía por nanoimpresión y electrodepósito. Analizamos en detalle la respuesta óptica de las estructuras, que dan lugar a grandes índices negativos desde el visible hasta el infrarrojo. Estudiamos su aplicación como sensores ópticos al infiltrar diferentes líquidos en las cavidades de aire. Estas técnicas son igualmente utilizadas para el desarrollo de plataformas metálicas nanoestructuradas para la observación de emisión espontánea colectiva.
Metamaterials are artificially structured materials, thoroughly designed for achieving electromagnetic properties not observed in nature such as the negative refractive index. The purpose of this thesis is the development of up-scalable optical metamaterials that can be easily incorporated into actual devices. By combining colloidal lithography and electrodeposition, we report an entirely bottom-up fishnet metamaterial made of gold and air layers. A proper theoretical and experimental design gives rise to tunable refractive index, from positive to negative values in the near infrared. This structure is extended to multilayered fishnet metamaterials made by nanoimprint lithography and electrodeposition. We thoroughly analyze the optical response of the structures, which lead to strong negative index from the visible to near infrared. Their performance as optical sensors is studied when infiltrating different liquids through the air cavities. These techniques are used to fabricate nanostructured metallic substrates for studying the collective spontaneous emission of fluorescent molecules.

A few computational models currently exist to predict heat production and dissipation in tissue when a tumor containing optically-tunable gold nanoparticles such as nanoshells or nanorods is illuminated with near infrared (NIR) laser. The validity of any computational model still needs to be established by experiments before its wide use for various future clinical applications. One of the possible ways to validate the model is through the heat measurements within a phantom made with tissue-equivalent heat-sensitive gel. Currently, there are a few recipes available for this type of gel and the majority of them use severely toxic ingredients. However, none of them seems to perfectly serve the current purposes. Therefore, the primary goal of this thesis work was to develop and characterize two new types of heat-sensitive gels, using relatively non-toxic substances for the in-phantom validation of computational models. Specifically, two novel agar based phantoms, TG1 and TG2, were developed and characterized. The basic optical response of these phantoms at 808 nm NIR light was determined to test their equivalency to human tissue. Thermal damage to the phantoms was quantified by heating them to specific temperatures and obtaining calibration curves to relate temperature and R2 relaxation rates. The phantoms were scanned with magnetic resonance imaging (MRI) to obtain T2 values. TG1 gel, agar and bovine serum albumin (BSA) mixture, was found not to be optically tissue-equivalent. However, TG1 gel demonstrated unambiguous digital response capable of distinguishing temperature of at least 70 °C compared to the sample receiving no heat. Additionally, TG1 gel produced high degree of linearity in the thermal therapy temperature regime (60 - 80 °C). TG2 gel containing agar mixed with BSA and Intralipid has exhibited tissue equivalency based on laser transmission measurements. TG2 gel exhibited heat damage based on T2 values, only when the temperature reaches 80 °C. This digital response is considered less sensitive in view of the fact that BSA starts to undergo denaturing and cause optical density change at approximately 70 °C. Both gels, however, have shown to be thermally stable at temperatures up to 80 °C with no evidence of gel melting being observed.

Le développement d’un procédé de polymérisation en émulsion est complexe de par la nature hétérogène de ce type de réaction. En outre, dans le cas de la polymérisation en émulsion du fluorure de vinylidène, la difficulté est d’autant plus accrue que le monomère est habituellement en phase gazeuse ou supercritique dans les conditions d’intérêt. Or la littérature manque d’informations concernant ce type de procédé de synthèse du PVDF sous une pression comprise entre 30 bar et 90 bar.Ainsi cette thèse a pour objectif de contribuer à une meilleure compréhension des mécanismes cinétiques et de stabilisation intervenants dans la polymérisation radicalaire en émulsion du VDF dans des conditions supercritiques et, plus particulièrement, de fournir des données expérimentales nécessaires à l’élaboration de futurs modèles.Avant même d’entreprendre les études expérimentales, cette thèse s’intéresse d’abord aux aspects d’installation et d’automatisation de l’unité de polymérisation ainsi qu’au démarrage et à l’optimisation du réacteur. Ensuite, plusieurs tests sont réalisés afin de comprendre certaines caractéristiques du latex produit ainsi que certaines propriétés du tensioactif fluoré. Une nouvelle méthode a spécialement été développée afin de suivre le phénomène de coagulation des particules de polymère.Finalement des réactions sont réalisées par lot et en semi-continu et une étude paramétrique des conditions opératoires et de la composition des réactifs est effectuée afin d’évaluer leur impact sur l’évolution de la polymérisation en émulsion. Notamment, le profil de vitesse de polymérisation est obtenu par calorimétrie, à partir d’une approche pratique fondée sur un estimateur d’état en cascade, ainsi que sur la mesure de la consommation de monomère, et sur l’analyse gravimétrique réalisée par prélèvement
The heterogeneous nature of the conventional emulsion polymerization can render the process quite complex. In the case of the emulsion polymerisation of vinylidene fluoride (VDF), the situation is more complicated than for the majority of industrial processes because the monomer is typically either a gas or a supercritical fluid under the polymerization conditions of interest. Given the relatively high pressure required for this process (30bar

Els objectius inicials d’aquesta tesi eren: 1) desenvolupar nanocatalitzadors amb composició, geometria i propietats estructurals ben controlades, 2) estudiar vies per a la incorporació de les nanopartícules prèviament sintetitzades en suports d’elevada àrea superficial i 3) estudiar i correlacionar les propietats i el comportament catalític dels nanocatalitzadors model sintetitzats. Per aquest motiu en una primera etapa s’ha estudiat la preparació de nanopartícules metàl·liques disperses i accessibles, a partir de les quals s’han fet créixer matrius mesoporoses amb porositat controlada. Concretament s’ha estudiat el mètode mitjançant la síntesi col·loïdal de nanopartícules d’or com a fase activa i en òxid de titani com a suport model i d’ interès. La porositat i àrea superficial del suport (TiO2) s’ha controlat mitjançant derivats carboxilats aromàtics, els quals actuen com a espaiadors físics entre centres de titani, generant una xarxa híbrida orgànica- inorgànica intermèdia. Per tal d’eliminar els lligands orgànics i estabilitzar el material, aquestes mostres s’han calcinat en aire. Mitjançant difracció de raigs-X i àrea B.E.T, s’ha confirmat la formació d’una xarxa mesoporosa abans i després de l’etapa de calcinació. Aquests resultats corroboren la funció dels lligands orgànics com a directors d’estructura, ja que proporcionen estabilitat tèrmica al material i el prevenen contra el col·lapse de l’estructura mesoporosa. Els materials mesoporosos finals eviten i bloquegen el creixement i l’agregació de les nanopartícules d’or, per tant minimitzen la sinterització que normalment té lloc en l’etapa de calcinació i incrementen les interaccions entre les nanopartícules metàl·liques i el suport. Finalment s’ha estudiat el comportament catalític d’aquests materials en dues reaccions d’interès: reacció d’oxidació de CO i la reacció de Water Gas Shift (WGS). La bona accessibilitat de les nanopartícules d’or ha estat confirmada amb una elevada conversió de CO a COR2R a baixa temperatura en la mostra Au@TiOR2R(b). Els resultats obtinguts per espectroscòpia DRIFT mostren una banda única i ben definida en el catalitzador Au@TiOR2R(b), que s’associa a espècies AuP característic dels enllaços Au-O-Ti de la interfície metall-suport. En una segona etapa s’han sintetitzat nanopartícules de coure, cobalt i s’ha desenvolupat una síntesi per a la preparació de nanopartícules bimetàl·liques de cobalt-coure amb estructura core shell, Co@Cu. Aquesta síntesi es basa en la substitució d’àtoms de cobalt per àtoms de coure mitjançant una reacció de desplaçament galvànic, que ha permès modular la composició en la nanopartícula. Per a la preparativa del nanocatalitzador, les nanopartícules han estat incorporades en una matriu mesoporosa de SiOR2R a través del mètode de la inclusió capil·lar. Els elevats valors de dispersió obtinguts, confirmen la mida nanomètrica de les nanopartícules i l’eficiència del mètode per a la seva incorporació. Mitjançant l’anàlisi de reducció tèrmica programada, s’ha observat un únic pic de reducció en les mostres Co@Cu-SiOR2 en un rang de temperatures intermedis als catalitzadors monometàl·lics. Aquests perfils mostren una una elevada homogeneïtat de la mostra i un contacte íntim entre el cobalt i el coure en les nanopartícules Co@Cu, així com un efecte sinèrgic en la reducció del cobalt i del coure. L’estudi de l’evolució de les nanopartícules durant els diferents tractaments ha mostrat una segregació de les fases en la nanopartícula, Co@Cu, en funció del tractament aplicat: la reducció a pressió i temperatura ha mostrat la segregació del cobalt en superfície donant una estructura core-shell inversa a la de les nanopartícules inicials. Finalment s’ha estudiat el comportament catalític en la reacció d’hidrogenació de CO2. Els nanocatalitzadors han mostrat capacitat per a la formació d’enllaços C-C i la formació d’alcohols, fet que posa de manifest un comportament sinèrgic i bifuncional en els centres bimetàl·lics. Tot i que , els resultats obtinguts en les conversions de CO2 R indiquen que la presència de cobalt en superfície és necessari per poder millorar el rendiment catalític d’aquest materials.
The goal set at the beginning of this thesis was the preparation of metallic nanoparticles via colloidal synthesis and its use in catalytic applications. The first point of interest was the synthesis of disperse and accessible Gold nanoparticles, that were used in the growth of a mesoporous Titanium oxide lattice. The porosity and superficial area of the support were controlled by carboxylic derivatives that act like physical spacers between de titanium centers and create a hybrid organic-inorganic lattice. In order to remove the organic ligands and to stabilize the material, samples were calcined. The formation of the mesoporous lattice, both before and after the calcinations, was confirmed by X-ray diffraction and B.E.T. area measurements. These results indicate that the carboxylic ligands provide the mesoporous structure with thermal stability and prevent its collapse. The final mesoporous materials efficiently blocked the aggregation and growth of the gold nanoparticles, minimizing their sintering during the calcination treatment and increasing the interaction strength between the metal nanoparticles and the oxide support. The catalytic behavior of these materials was studied in two reactions of interest: CO oxidation and Water Gas Shift (WGS). The obtained results confirmed the catalytic activity and its dependence with the size of the nanometric Gold particles and the interaction established between the metal and the support. The second point of interest was the preparation, using the colloidal synthesis, of Copper and Cobalt nanoparticles, as well as Copper-Cobalt bimetallic nanoparticles with core-shell structure (Co@Cu). The synthesis of these Co@Cu nanoparticles is based on the substitution of Cobalt by Copper atoms as a result of a redox reaction that permitted the synthesis of nanoparticles with different Cu/Co ratio. Moreover, the obtained nanoparticles were incorporated in a SiO2 mesoporous support by means of capillary inclusion. The final catalysts were chemically and structurally characterized with DRX, ICP, TEM, HRTEM, TPR and B.E.T. area.

[ES] En la presente Tesis Doctoral se investigó la aplicación del proceso de ultrafiltración (UF) y el fenómeno de ensuciamiento de las membranas en la eliminación de sustancias disueltas y coloidales (DCS) de efluentes tratados de la industria papelera (PMTE) para su reutilización en los diferentes procesos de fabricación de papel y cartón reciclado. El objetivo general de esta investigación se dividió en tres partes principales: i) describe cómo encontrar las condiciones óptimas de operación de cuatro parámetros de proceso: presión transmembrana (TMP), velocidad de flujo cruzado (CFV), temperatura y corte de peso molecular (MWCO) para maximizar el flujo promedio de permeado (Jp) y rechazo de la demanda química de oxígeno (COD) y minimizar el descenso del flujo de permeado acumulado (SFD) utilizando el método de Taguchi (Design Robusto) y utility concept aplicado a un proceso de UF a flujo cruzado, para remover DCS de efluentes tratados de la industria papelera, ii) el descenso del flujo de permeado y los mecanismos de ensuciamiento de las membranas de UF ensuciadas con PMTE se examinaron mediante modelos matemáticos semi-empíricos. Los resultados para los diferentes ensayos de UF se expresaron en términos de variación del Jp en función del tiempo para verificar la precisión del ajuste (mayor valor de R2 y menor valor de desviación estándar) de los distintos modelos de Hermia adaptados a flujo tangencial y del modelo de formación de torta en filtración a presión constante ajustados a los datos experimentales, y iii) describe métodos de identificación, caracterización y posibles orígenes de las sustancias contaminantes (foulants) en las membranas de UF. Técnicas como el análisis físico-química, FESEM, SEM-EDS, ATR-FTIR y 3DEEM se llevaron a cabo para comprender qué fracción de los contaminantes son responsables por la formación de incrustaciones en las membranas. Los resultados obtenidos durante la etapa de optimización de parámetros del procesos demostraron que TMP y MWCO tienen la mayor contribución en el Jp y SFD. En el caso de la tasa de rechazo de COD, los resultados mostraron que MWCO tiene la mayor contribución seguida de CFV. Por consiguiente, las condiciones óptimas se encontraron para el segundo nivel de TMP (2.0 bar), el tercer nivel del CFV (1.041 m/s), el segundo nivel de la temperatura (15°C) y el tercer nivel de MWCO (100 kDa). Bajo estas condiciones óptimas de operación Jp, rechazo de COD y SFD alcanzaron respuestas de 81.15 L/m2.h, 43.90% y 6.01 (alrededor de 28.96 % para (FD), respectivamente, valores dentro del rango previsto del intervalo de confianza del 95%. Además, los modelos de Hermia adaptados a UF en flujo tangencial fueron capaces de predecir con gran precisión el descenso del Jp y los mecanismos de ensuciamiento en función del tiempo para todas las membranas seleccionadas (10, 30 y 100 kDa) y bajo diferentes condiciones ensayadas de UF. Por lo tanto, los modelos que presentan un mayor grado de ajuste son el bloqueo completo de poros (coeficiente de determinación R2 >0.97) y bloqueo intermedio (R2 >0.96), seguido por el modelo de formación de torta (R2 >0.94), lo que indica que estés son los principales mecanismos de ensuciamiento de las membranas. Análisis de 3DEEM revelaron que la mayoría de la materia orgánica fluorescentes en las membranas sucias eran proteínas coloidales (componentes similares a proteínas I + II) y proteínas macromoleculares (componentes similares a SMP). Además, polisacáridos (especie celulósica) y sustancias como ácidos grasos y resinosos fueron identificadas en las membranas contaminadas mediante análisis ATR-FTIR. Por fin, análisis SEM-EDS para las membranas ensuciadas con PMTE se detectó concentración de contaminantes inorgánicos (iones metálicos multivalentes) especialmente el Ca2+ que podría acelerar la formación torta en la superficie de la membrana.
[CA] En la present Tesi Doctoral es va investigar l'aplicació del procés d'ultrafiltració (UF) i el fenomen d'embrutiment de les membranes en l'eliminació de substàncies dissoltes i col·loïdals (DCS) d'efluents tractats de la indústria paperera (PMTE) per al seu reutilització en els diferents processos de fabricació de paper i cartó reciclatge. L'objectiu general d'aquesta investigació es va dividir en tres parts principals: i) descriu com trobar les condicions òptimes d'operació de quatre paràmetres de procés: pressió transmembrana (TMP), velocitat de flux creuat (CFV), temperatura i tall de pes molecular (MWCO) per a maximitzar el flux mitjà de permeat (Jp) i rebuig de la demanda química d'oxigen (COD) i minimitzar el descens del flux de permeado acumulat (SFD) utilitzant el mètode de Taguchi (Design Robust) i utility concept aplicat a un procés de UF a flux creuat en escala pilot, per a remoure DCS d'efluents tractats de la indústria paperera (PMTE), ii) el descens del flux de permeat i els mecanismes de embrutiment (fouling) de les membranes de UF embrutades amb PMTE es van examinar mitjançant models matemàtics semi-empírics. Els resultats per als diferents assajos de UF es van expressar en termes de variació del flux de permeat (Jp) en funció del temps per a verificar la precisió de l'ajust (major valor de R2 i menor valor de desviació estàndard) dels diferents models de Hermia adaptats a flux tangencial i del model de formació de coca en filtració a pressió constant ajustats a les dades experimentals, i iii) descriu mètodes d'identificació, caracterització i possibles orígens de les substàncies contaminants (foulants) en les membranes de UF. Tècniques com l'anàlisi física-química, FESEM, SEM-EDS, ATR-FTIR i 3DEEM es van dur a terme per a comprendre quina fracció dels contaminants són responsables per la formació d'incrustacions sobre la superfície i adsorció dins dels porus de les membranes. Els resultats obtinguts durant l'etapa d'optimització de paràmetres del processos van demostrar que TMP i MWCO tenen la major contribució en el Jp i SFD. En el cas de la taxa de rebuig de COD, els resultats van mostrar que MWCO té la major contribució seguida de CFV. Per consegüent, les condicions òptimes es van trobar per al segon nivell de TMP (2.0 bar), el tercer nivell del CFV (1.041 m/s), el segon nivell de la temperatura (15°C) i el tercer nivell de MWCO (100 kDa). Sota aquestes condicions òptimes d'operació Jp, rebuig de COD i SFD van aconseguir respostes de 81.15 L/m².h, 43.90% i 6.01 (al voltant de 28.96% per a (FD)), respectivament, valors dins del rang previst de l'interval de confiança del 95%. A més, els models de Hermia adaptats a UF en flux tangencial van ser capaços de predir amb gran precisió el descens del Jp i els mecanismes de embrutiment en funció del temps per a totes les membranes seleccionades (10, 30 i 100 kDa) i baix diferents condicions assajades de UF. Per tant, els models que presenten un major grau d'ajust són el bloqueig complet de porus (coeficient de determinació R2 >0.97) i bloqueig intermedi (R2 >0.96), seguit pel model de formació de coca (R2 >0.94), la qual cosa indica que estigues són els principals mecanismes de embrutiment de les membranes. Anàlisi de 3DEEM van revelar que la majoria de la matèria orgànica fluorescents en les membranes brutes eren proteïnes col·loidals (components similars a proteïnes I + II) i proteïnes macromoleculars (components similars a SMP). A més, polisacàrids (espècie cel·lulòsica) i substàncies com a àcids grassos i resinosos van ser identificades en les membranes contaminades mitjançant anàlisis ATR-FTIR, tals substàncies exerceixen un paper important en el embrutiment de les membranes. Per fi, anàlisi SEM-EDS per a les membranes embrutades amb PMTE es va detectar concentració de contaminants inorgànics (ions metàl·lics multivalents) especialment el Ca2+ que podria accelerar la formació coca en la àrea de la membrana.
[EN] In this PhD Thesis, the application of ultrafiltration process (UF) and membrane fouling phenomenon used to remove dissolved and colloidal substances (DCS) from paper mill treated effluent (PMTE) for reuse in different recycled paper and cardboard manufacturing processes was investigated. The overall goal of this research has been divided into three main parts: i) describes how to find optimal operating conditions of four controlling parameters, such as transmembrane pressure (TMP), cross-flow velocity (CFV), temperature and molecular weight cut-off (MWCO) for maximizing the average permeate flux (Jp) and chemical oxygen demand (COD) rejection, and minimizing the cumulative flux decline (SFD) using Taguchi method and utility concept for a cross-flow UF in pilot scale, used to remove DCS from a paper mill treated effluent (PMTE), ii) flux decline and fouling mechanisms of UF membranes fouled with PMTE were examined by theoretical modelling. The results from UF tests were expressed in terms of permeate flux (Jp) as a function of time to check modified Hermia's models adapted to crossflow filtration and cake formation in constant-pressure filtration, and iii) describes the Identification, characterization and possible origins of UF membrane foulants. Techniques such as chemical analysis, FESEM, SEM-EDS, ATR-FTIR and 3DEEM analysis were applied to understand which fraction of the foulants caused the fouling. This research found that the TMP and MWCO have the greatest contribution to the average permeate flux and SFD. In the case of the COD rejection rate, the results showed that MWCO has the highest contribution followed by CFV. The optimum conditions were found to be the second level of TMP (2.0 bar), the third level of the CFV (1.041 m/s), the second level of the temperature (15°C), and the third level of MWCO (100 kDa). Under these optimum conditions Jp, COD rejection and SFD resistance of 81.15 L/m2/h, 43.90% and 6.01 (around 28.96 % of (FD), respectively, were obtained and they were within of the predicted range at the 95% confidence interval. Furthermore, the results showed that the predictions of the modified Hermia's models adapted to cross-flow UF had good agreements with experimental data, under different conditions tested for PMTE. Therefore, it can be concluded that for all cases the best fit (higher accuracy) to the experimental data corresponds to the complete (coefficient of determination R2 >0.97) and intermediate (R2 >0.96) blocking, followed by the cake layer formation (R2 >0.94). Moreover, measurements of particle size distribution and zeta potential near the isoelectric point, showed a substantial reduction in colloidal compounds. The 3DEEM analysis revealed that the majority of the organic foulants with fluorescence characteristics on the fouled membranes were colloidal proteins (protein-like substances I+II) and macromolecular proteins (SMP-like substances). Further, polysaccharide (cellulosic specie), fatty and resin acid substances were identified on the fouled membrane by the ATR-FTIR analysis and they play an important role in membrane fouling. In addition, the membrane SEM-EDS analysis showed accumulate and adsorbed onto the membrane surfaces of inorganic foulants, such as multivalent metal ions and especially Ca2+ (acts as a binding agent) that could accelerate cake layer formation on the membrane.
Santos Sousa, MR. (2020). Optimization of Operation Parameters in Ultrafiltration by Experiment Design, Mathematical Modelling and Fouling Characterization of the Membranes Used to Remove Dissolved and Colloidal Substances from a Treated Paper Mill Effluent [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/155975
TESIS

Ce travail concerne l'etude de gelification, les etudes des proprietes physiques et des proprietes electriques de gel polydimethylsiloxane (pdms) reticule. L'elasticite du milieu est caracterisee par des grandeurs macroscopiques : le taux de gonflement a l'equilibre, le module elastique et le module dynamique. A l'echelle des mailles du reseau, les mesures de relaxation magnetique nucleaire (rmn) revelent l'etat de contrainte des segments de chaines definis entre deux points d'ancrage (noeuds de reticulation, enchvetrements). Chaque etat de gelification est identifie par une variable calculee dans le cadre de l'approximation de l'arbre de cayley. Les parametres rmn observes ainsi que les grandeurs macroscopiques mesurees sont fonction de cette variable. Deux comportements ont ete mis en evidence pour la gelification : l'un, pres du seuil de percolation, se manifeste par une evolution des grandeurs physiques qui suivent des lois de puissance, l'autre, loin du seuil de percolation, evolue selon une fonction lineaire de la variable. Les gels pdms vulcanises et gonfles ont un comportement identique a celui d'un systeme des chaines polymeres branchees considere a la concentration de recouvrement. Les resultats de rmn ont montre que le parametre structural #c est caracteristique de l'elasticite et de l'effet d'enchevetrements du reseau. En general, l'elasticite du gel pdms observee par les mesures macroscopiques est une fonction lineaire de sa structure du reseau detecte par la rmn. Cette relation est observee pour les gels charges ou non. Les proprietes electriques des gels pdms, mises en evidence par les mesures conventionnelles ou par le declin du potentiel de surface (dps), paraissent etre influencees par leur reseaux reticules, en particulier par l'existence des petites chaines qui subsistent apres la formation du reseau.