Thèses sur le sujet « Emulsione Pickering »

L’industria degli pneumatici si prefigge di indagare possibili strategie sintetiche per ridurre l’impatto ambientale durante tutto il ciclo di vita dello pneumatico, attraverso l’uso di materiali sostenibili e lo sviluppo di tecniche innovative che riducano il consumo di energia e le emissioni di CO2. In questo contesto, questa progetto di dottorato è focalizzato sulla preparazione di nanocompositi eco-sostenibili attraverso l’uso di un approccio colloidale per aumentare la dispersione di filler idrofilici, in linea con i nuovi requisiti di sostenibilità delle politiche europee. L’approccio colloidale punta a produrre nanocompositi con filler idrofilici, la cui efficiente dispersione attraverso tecniche di miscelazione tradizionali rimane difficoltosa a causa della scarsa compatibilità con la matrice organica. Questa tecnica si focalizza sull’incremento della dispersione di filler senza alcuna modifica superficiale, con l’eliminazione delle poveri prodotte durante il mescolamento con significativi benefici per l’ambiente e i lavoratori. Due diversi approcci colloidali sono stati utilizzati: i) una tecnica di miscelazione in lattice e ii) una in situ polimerizzazione in emulsione per la produzione di nanocompositi altamente caricati contenenti filler come silice e sepiolite (Sep), questi ultimi sono considerati filler promettenti nell’ambito del rinforzo dei polimeri grazie alla loro struttura fibrosa e all’elevato rapporto di forma. La concentrazione, la carica, la forma dei nanofiller a base silicea sono stati studiati come parametri rilevanti per la stabilizzazione e destabilizzazione di lattici a base di poliisoprene naturale e sintetico. Una efficiente procedura di miscelazione in lattice è stata messa a punto per produrre compositi eco-sostenibili, chiamati masterbatches (MBs), attraverso l’incorporazione di silice o Sep nel lattice di gomma naturale (emulsione in acqua di cis-1,4-poliisoprene), attraverso la flocculazione (aggregazione risultante dalla coesione di particelle di polimero) di una miscela acquosa di nanofiller a base silicea e gomma. La tecnica di miscelazione in lattice ha dimostrato di favorire una omogenea dispersione di fibre di sepiolite idrofilica in matrice di gomma. La principali caratteristiche fisico-chimiche che controllano i processi di aggregazione in acqua come il pH, il potenziale Z, la concentrazione, assieme alle caratteristiche morfologiche del MB Sep-gomma naturale, sono state prese in considerazione allo scopo di investigare le interazioni Sep-gomma naturale. E’ stato proposto un meccanismo di flocculazione basato su attrazioni elettrostatiche e depletive, connesso all’elevato contenuto di filler (50% in peso) e alla peculiare anisotropia delle particelle di Sep. Inoltre, i MBs sono stati utilizzati per preparare compositi sostenibili attraverso la combinazione di miscelazione in lattice e mescolazione meccanica. Questo approccio combinato sfrutta la buona distribuzione del filler e previene il rilascio di polveri durante il processo. Una polimerizzazione Pickering in situ è stata considerata come alternativa per la produzione di nanocompositi eco-sostenibili. Particelle poliisoprene/filler a base silicea sono state sintetizzate sfruttando dell’effetto stabilizzante di filler inorganici che agiscono come tensioattivi riducendo la tensione superficiale e stabilizzando l’emulsione. Sulla base dei nostri risultati, viene suggerito un possibile meccanismo di polimerizzazione in emulsione stabilizzata da particelle solide. In conclusione, l’approccio colloidale, basato su miscelazione in lattice e polimerizzazione Pickering in situ, può essere considerato un metodo sostenibile, semplice ed efficace adatto per applicazioni tecnologiche altamente performanti. I risultati indicano che le strategie utilizzate sono adatte per produrre nanocompositi altamente caricati di filler a base silicea.
Sustainability has become a field of great interest in the world industry. For the scientific community the challenge lies in the identification of green synthetic approaches and new alternatives to petroleum-based materials. In the case of the tyre industry, the challenge is to identify possible design strategies and alternatives to reduce the environmental impact throughout the life cycle of tyres, by means of both the use of environmentally friendly materials and the development of innovative products, having reduced energy consumption and CO2 emissions. In this context, this PhD thesis is focused on the preparation of eco-friendly silica-based nanocomposites by using a colloidal approach to increase the dispersion of hydrophilic fillers in line with the new requirements of sustainability from the EU policies. The colloidal approach aims at compounding nanocomposites with hydrophilic fillers, whose efficient dispersion through traditional mixing still remains a challenging issue, due to their poor compatibility with the organic matrix. This technique aims at increasing the filler dispersion without any expensive surface modification, with the elimination of the volatile component released during mixing, producing significant benefits for environment and workers. Two different colloidal approaches were applied: i) latex compounding technique (LCT) and ii) in situ emulsion polymerization to prepare highly-loaded nanocomposite rubber materials containing silica-based fillers, silica and sepiolite (Sep) clay, considered a promising filler candidate for the polymer strengthening due to its fibrous structure and high particle aspect ratio (AR). The concentration, the charge and the shape of silica-based nanofillers were studied as relevant parameters on stabilization and destabilization of natural and synthetic polyisoprene latexes. An effective LCT procedure was established to produce eco-friendly composites, namely masterbaches (MBs), by incorporating silica or Sep into natural rubber latex (i.e. emulsion in water of cis-1,4-polyisoprene), through the flocculation (i.e. aggregation resulting from the bridging of polymer particles) of the silica-based nanofillers/rubber mixed aqueous system. LCT showed to favour a homogeneous dispersion of hydrophilic Sep fibers in the rubber matrix. The main physicochemical parameters which control aggregation processes in the aqueous medium, i.e. pH, -potential, concentration, as well as the morphological features of the final Sep-natural rubber MBs, were comprehensively investigated helping to figure out the Sep-NR interactions and to propose a flocculation mechanism, based on electrostatic and depletion attraction forces, remarkably connected both to the high content (50 wt.%) and to the peculiar anisotropy of Sep fibers. Furthermore, the MBs with high filler loadings were used to produce environmentally friendly composites, by combining LTC and melt mixing. This combined approach could take advantage of the good filler distribution and prevents dust from floating in the air during processing. In situ Pickering polymerization was considered as an alternative colloidal approach to produce eco-friendly nanocomposites. Polyisoprene/silica-based structured particles were synthesized on the base of the stabilizing effects of inorganic fillers which act like surfactants lowering the interfacial tension and stabilizing the emulsion. On the basis of our results, we suggested a possible mechanism for emulsion polymerizations stabilized by solid particles. In conclusion, the colloidal approach, based on both LTC and in situ Pickering emulsion polymerization, can be considered as green, simple and effective method suitable for high-performance technological applications. The outcomes indicate the suitability of the adopted strategies as a sustainable procedure for the production of high-loaded silica based-rubber nanocomposites.

Particle stabilized emulsions, also known as Pickering emulsions, have been widely used in many industry applications. While the breadth of potential applications for Pickering emulsions keeps growing, our fundamental understanding of Pickering emulsions is still poor. My thesis work addresses both fundamentals and applications of particle stabilized emulsions. In the fundamental part of this thesis work, we investigated the effects of particle charge on particle adsorption and the particle contact angle, and to investigate their ensuing consequences for the stability of Pickering emulsions. We provided the first experimental hint that the widely overlooked image charge repulsion can hinder the adsorption of particle to the oil-water interface and prevent the formation of Pickering emulsions. Consistently with the experimental suggestion, our theoretical model also confirmed that the image charge repulsion has the right order of magnitude, relative to the other forces acting on the particle, to impede particle adsorption and Pickering emulsification. For the conditions in which particle adsorption to the liquid interface does occur, the particle contact angle will play an important role in influencing the stability and type of Pickering emulsions. Our experimental work showed that the equilibrium contact angle of particles at interfaces and the type of emulsions preferentially stabilized by these particles can be strongly affected by the particles' charging state, which we attribute to a free energy contribution from the electric field set up by the charged particle and its asymmetric counterion cloud. A very simplistic calculation considering only the dipole field as the leading contribution and treating the water phase as a perfect conductor, found that the energy stored in the field is indeed strong enough and shows sufficient variation with the particle position to shift the equilibrium position significantly from where it would be based on interfacial tension alone. In a separate, more application oriented part of this thesis work, we have fabricated microcapsules from double Pickering emulsions and demonstrated that the combined use of hard silica particles and pH-responsive dissoluble polymer particles at the emulsion interface imparts a combination of pH-responsiveness (stimulated pore opening) and structural integrity to resulting capsules. We have further demonstrated the first double Pickering emulsion templated capsules in which interfacial polymerization was carried out at both emulsion interfaces, yielding a capsule with two composite shells, composed of polyurethane and silica particles, and characterized the transport of a model cargo through the capsules walls as well as the capsules' mechanical properties.

Water-in-oil-in-water (W/O/W) double emulsion systems provide an innovative approach for the development of low-fat healthier foods. By replacing a proportion of the oil phase of a simple oil-in-water (O/W) emulsion with an internal water phase, the overall oil volume within the emulsion system can be decreased, with potentially negligible changes to its organoleptic properties. However, double emulsions are notoriously unstable for adequate periods of time, largely due to the existence of two oppositely curved water-oil (W/O) and oil-water (O/W) interfaces in close proximity. The present study investigates the use of Pickering stabilisation in order to enhance the stability of double emulsions. Pickering stabilisation mechanisms are reputed for superior, longer term stabilisation capacities when compared to conventional surfactant stabilised emulsions, but edible particles with Pickering functionality are scarce. The work in this thesis explores the impact of introducing Pickering stabilisation to a double emulsion structure, initially at only one of the two water/oil interfaces (either W/O or O/W) and ultimately across the entire interfacial areas. Initial work conducted centred on investigating the role of a range of edible particulates as potential Pickering stabilisers in simple emulsions (both W/O and O/W emulsion types). Based on the knowledge gained from these studies, a range of Pickering-Surfactant stabilised double emulsions (with particles or surfactant stabilising alternate interfaces), using a range of surfactants, and Pickering only stabilised double emulsion systems were prepared and analysed in terms of their microstructure, stability and encapsulation efficiencies.

This doctoral thesis highlights the most interesting experimental results achieved between 2015 and 2018 by the author, during his stay in the laboratories of the Department of Chemical Sciences of the University of Padova. The fil rouge of this thesis work is Pickering Emulsions (PE); emulsions where solid particles alone are used as stabilizers instead of the typical molecular or macromolecular surfactants that are employed to produce widely used emulsions in pharmaceutics, drug delivery, cosmetics, food industry to name a few. Solid micro/nanoparticles accumulate at the interface between two immiscible liquids (typically denoted as oil and water phase) and stabilize droplets against coalescence. A great advantage of a PE is that it is relatively stable once made and that many solid particles can be endowed with useful characteristics: conductivity, responsiveness, porosity, catalysis and so on. The chemical modification of silica nanoparticles (SiNP) and their use as PE stabilizers is the first theme treated in this thesis work. SiNP are functionalized with hydrophobic molecular structures for tuning their wettability, and with photo-active moieties to impart photocatalytic properties. In addition, silica-based PE are used to confine special ingredients needed for the colorimetric detection of acetone whose presence is associated to triacetone triperoxide, a deadly explosive used by terrorists in recent attacks, and for the development of a testing kit in the form of a pen. Another interesting PE stabilizer is nanocrystalline cellulose (NCC). An extensive sperimentation was carried out to learn how to handle and to chemically functionalize NCC. This led to the development of robust protocols that allowed to install on cellulose nanocrystals a pH-sensitive dye and magnetic nanoparticles that were used to develop, as a proof of principle, a solid pH sensor for urea detection and a colorimetric/magnetic, doubly-responsive system. The modified NCC materials hold the potential as PE stabilizers whose study is underway. The last part of the thesis reports the study, in collaboration with prof. S. Gross of the Chemical Sciences Department in Padova and prof. E. Hensen of the University of Eindhoven, for the production of ZnS nanoparticles through a controlled nucleation and crystallization under continuous flow conditions at room temperature, in water and without the use of any stabilizing ligand. The colloids display an average size of 5 nm and an impressively high specific surface area of 287 m2/g. Nanostructured ZnS is well known to be a direct wide-bandgap semiconductor and, for its tunable photophysical and electrochemical properties, is used for a broad range of applications ranging from catalysis and photocatalysis to nonlinear optics, optoelectronic devices and optical bioimaging. The possibility to prepare stable nanoparticles without the need of special ligand stabilization open the interesting perspective to use those as-prepared particles directly from the continuous flow reactor to stabilize functional PE. Work in this direction is currently underway. Furthermore, a toolbox that was always available during this thesis work was flow chemistry, an ensemble of techniques for the manipulation of fluids on the micrometer scale. Such manipulation is carried out inside microchannels, confined environments whose geometries can be exploited to optimize unit operations – such as mixing and heat transfer – of profound interest for chemists. A flow chemistry approach was used to prepare ZnS nanoparticles and also to develop a selective bromination protocol of tetraphenyl porphyrins. This latter study, along with a study on the application of functionalized NCC as a flame retardant have been a unique opportunity to face interesting problems, although they were not related to the Pickering emulsions general theme of this thesis work.

L’objectif du présent projet est de développer une méthodologie pour la modélisation fondamentale de procédés de polymérisation en émulsion sans tensioactif stabilisés par des particules inorganiques, dénommées "polymérisation en émulsion Pickering". La modélisation des systèmes de polymérisation en émulsion nécessite la modélisation de la distribution de taille des particules (PSD), qui est une propriété importante d'utilisation finale du latex. Cette PSD comprend des sous-modèles dédiés à la nucléation des particules, le transfert de masse entre les différentes phases (monomère, radicaux, stabilisant) et la coagulation des particules. Ces modèles devraient de préférence être validés expérimentalement de manière individuelle. La première partie principale du travail est consacrée à l'étude expérimentale. Cette partie peut être divisée en trois parties. La première partie décrit l'adsorption de particules inorganiques sur le polymère sans réaction. Une adsorption multicouche a été observée et l’isotherme B.E.T. a été capable de décrire cette adsorption. L'adsorption se révèle être plus importante pour une force ionique plus élevée. La dynamique d'adsorption semple être rapide et par conséquent le partage peut être considéré à l'équilibre pendant la polymérisation. La deuxième partie concerne l'étude de différents paramètres de réaction sur le nombre de particules et la vitesse de réaction dans des polymérisations ab initio. L'effet du mélange, de la concentration initiale des monomères et de la concentration de l'initiateur a été étudié. L'optimisation de ces conditions a été utile pour la partie de modélisation. La dernière partie décrit les différences entre plusieurs Laponite® à travers la polymérisation en émulsion ab initio du styrène.La deuxième partie principale du manuscrit a porté sur la modélisation de la polymérisation en émulsion Pickering. Le modèle de bilan de population et le nombre moyen de radicaux par particule ont été calculés en fonction de l'effet des particules organiques. La croissance des particules de polymère a été optimisée en ajustant les modèles d'entrée et de désorption des radicaux décrits dans la littérature aux données expérimentales. Aucune modification n'a été nécessaire, ce qui nous a permis de conclure que l'argile n'avait aucune influence sur l'échange radical. Cependant, la stabilisation joue un rôle important dans la production de particules de polymère. Le modèle de nucléation coagulante a été capable de décrire le taux de nucléation et de prédire le nombre total de particules
The aim of the present project is to develop a methodology for fundamental modeling of surfactant-free emulsion polymerization processes stabilized by inorganic particles, referred to as “Pickering emulsion polymerization”. Modeling emulsion polymerization systems requires modeling the particle size distribution (PSD), which is an important end-use property of the latex. This PSD includes submodels dedicated to particle nucleation, mass transfer between the different phases (monomer, radicals, stabilizer), and particle coagulation. These models should preferably be individually identified and validated experimentally. The first main part of the work is dedicated to the experimental study. This part can be divided in three parts. The first part describes the adsorption of inorganic particles on polymer without reaction. Multilayer adsorption was observed and B.E.T. isotherm was able to describe this adsorption. The adsorption was found to be enhanced at higher ionic strength. The adsorption dynamics were found fast and therefore clay partitioning can be considered at equilibrium during polymerization. The second part concerned the investigation of different reaction parameters on the particles number and reaction rate in ab initio polymerizations. The effect of mixing, initial monomer concentration and initiator concentration were considered. Optimization of these conditions was useful for the modeling part. The last part described the differences between several LaponiteR_ grades through the ab initio emulsion polymerization of styrene. The second main part of the manuscript focused on the modeling of the Pickering emulsion polymerization. The population balance model and average number of radicals balance were adapted regarding the effect of inxi organic particles. The growth of the polymer particles was optimized by fitting the models of radicals’ entry and desorption described available in literature to the experimental data. No modification was needed, which allowed us to conclude that the clay had no influence on radical exchange. However, LaponiteR_ stabilization played an important role in polymer particles production. Coagulative nucleation model was able to describe the nucleation rate and predict the total number of particles

The design of nanocomposites, which typically consist of polymeric matrices with embedded particles having at least one characteristic length in the nanometer range, has recently been the focus of a great attention. Nanocomposites, in a large variety of morphologies and distinct compositions are already on the market. In this context, the construction of novel porous nanocomposites, exhibiting hierarchical structures, will allow the development of innovative advanced materials with promising applications in many fields: catalysis, gas/liquid storage, gas purification, etc. The use of highly concentrated phase emulsions (HIPEs) as templates has been shown to be an effective route for the preparation of macroporous polymers. Specifically, the use of suitable surface-modified inorganic oxide nanoparticles as emulsions stabilizers (so called Pickering emulsions) provide an alternative approach to the classical surfactant-based systems, to obtain such hybrid organic-inorganic nanocomposite porous materials. Thanks to the ability of finely-divided solids to adsorb spontaneously at liquid-liquid interfaces, any functionality coming from the nanoparticles can be imparted to the materials, in a single-step preparation method. It has been described that, the resulting macroporous nanocomposites, obtained in Pickering highly concentrated emulsions, typically exhibit closed-cell structures and rather large pore sizes. These drawbacks are frequently overcome by combining simultaneously surfactants and particles. Nevertheless, there is a lack of systematic study on how the interactions between these two emulsifiers influence the final physicochemical properties of the materials obtained. For instance, contrary to what is often expected, the addition of particles to a surfactant-stabilized emulsion or inversely, the addition of surfactant to a particle-stabilized emulsion can negatively influence its stability, rather than enhance it. The main objective of this research work was to investigate the formation of polymeric macroporous nanocomposites with embedded functional nanoparticles, using W/O highly concentrated emulsions as templates. For this purpose, two kinds of nanoparticles with interesting functionalities have been used: - Superparamagnetic iron oxide nanoparticles - Titanium dioxide photocatalytic nanoparticles Styrene and the crosslinker divinylbenzene are used in the emulsion continuous phase, as a model monomer system. The emulsions are processed into macroporous materials by free-radical polymerization of such a continuous phase. In all cases, nanoparticles are included in the systems, and three different types of emulsions are studied using different approaches: (a) HIPEs stabilized with surfactants and prepared by the phase inversion method, containing nanoparticles inside the continuous phase. (b) HIPEs stabilized with nanoparticles, in absence of surfactant and prepared by the drop-wise addition method. The use of Pickering emulsions to obtain nanocomposite materials constitutes a very novel approach, recently first described. (c) HIPEs stabilized primary with nanoparticles with increasing amounts of surfactant molecules, prepared by the drop-wise addition method. In this work, special emphasis has been given to the study of the individual contribution of either nanoparticles or surfactants on the (in)stability of the resultant highly concentrated emulsions. Moreover, the precise role that each emulsifier plays, focusing on their interactions and the related emulsion stabilization mechanisms, has been investigated. In addition, we have study the arrangement of the nanoparticles in the resulting porous nanocomposites, with respect to several parameters such as particle size or surfactant concentration. Likewise, the main physical properties of the materials, such as macroporous structure, porosity, permeability or mechanical strength, have been compared. Finally, the magnetic properties and photocatalytic activity of the nanocomposite materials, which contained iron oxide and titanium dioxide nanoparticles, respectively, have been characterized.
La preparación de materiales constituidos por una matriz polimérica que contiene algún tipo de elemento inorgánico, como nanopartículas o nanotubos, ha generado durante los últimos años un enorme interés científico. Generalmente, estos materiales se denominan nanocompuestos. Actualmente, existen productos en el mercado en forma de sensores ópticos o productos en fase de desarrollo comercial, como poliolefinas reforzadas con arcilla en la industria automovilística. Uno de los campos de mayor actividad es la fabricación de materiales porosos avanzados, con aplicaciones en campos tan variados como el de membranas, purificación de gases o almacenamiento de líquidos/gases. Este trabajo de tesis tiene como objetivo principal el de obtener nanocomposites macroporosos con nanopartículas incorporadas, utilizando emulsiones altamente concentradas como plantilla. Para ello se han empleado emulsiones del tipo agua en aceite, estabilizadas tanto con tensioactivos como con nanopartículas (denominadas emulsiones de Pickering). La obtención de nanocompuestos macroporosos utilizando emulsiones de Pickering constituye un método novedoso descrito por primera vez recientemente. Con este propósito, se han utilizado dos tipos de nanopartículas funcionales: nanopartículas superparamagnéticas de óxido de hierro y nanopartículas fotocatalíticas de dióxido de titanio. Ambas han sido previamente funcionalizadas con ácido oleico para conferir hidrofobicidad a su superficie. Para obtener los materiales poliméricos, se ha llevado a cabo una polimerización entre el monómero estireno y el entrecruzante divinilbenceno en la fase externa de las emulsiones. De esta forma, se han obtenido materiales poliméricos porosos con nuevas funcionalidades magnéticas y fotocatalíticas. En primera instancia, se ha evaluado la interacción entre los dos emulsionantes empleados, nanopartículas y tensioactivos, y sus implicaciones en la estabilidad de las emulsiones altamente concentradas iniciales. Además, se ha estudiado la distribución de las nanopartículas en los materiales macroporosos obtenidos, en función de diversos parámetros como el tamaño o concentración de nanopartículas. Finalmente, se ha llevado a cabo una exhaustiva caracterización de las propiedades físicas de los materiales, tal como estructura macroporosa, porosidad, resistencia a la compresión o permeabilidad. También, se han estudiado las propiedades magnéticas y fotocatalíticas de los nanocompuestos, que contienen nanopartículas de óxido de hierro y de dióxido de titanio, respectivamente.

Much research has been carried out in recent years on Pickering emulsions, but understanding of the underlying physics requires considerable strengthening. This thesis seeks to address several fundamental aspects by presenting the results of recent experimental work. This work has focused on a model oil-in-water emulsion system stabilised by fluorescent colloidal silica particles and using a mixture of dodecane and isopropyl myristate as the oil phase. The phase behaviour of the particle dispersions has been altered using sodium chloride and sodium iodide, whilst sodium hydroxide and hydrochloric acid have been used to adjust the pH of samples. Comparisons are also made to emulsions stabilised by commercially available fumed silica. Conventionally, it was assumed that a weakly flocculating particle dispersion is required in order to generate a stable Pickering emulsion. It is shown in this work, however, that in some circumstances a weakly flocculating dispersion leads to the least stable emulsion. It is therefore argued that a more nuanced view of Pickering stabilisation is required, taking into account the factors affecting whether particles will adsorb to the interface during emulsification. Very recently it has begun to be suspected that Pickering emulsions sometimes aggregate due to the sharing of particles between two droplets, an effect known as bridging. In this thesis it is also shown that particle bridges can form in Pickering emulsions at high shear, and that they can subsequently be broken by low shear or by modifying the particle wettability. For the first time, electron microscopy has been used to provide direct evidence of droplets sharing particles. A simple theoretical model is developed, based on collisions between partially coated droplets, which captures the trends observed experimentally. It is argued that particle bridging may have been overlooked in the literature, and that the shear history of emulsions is a crucial determinant of subsequent behaviour. The deaggregation of bridged emulsions has been studied using a novel method where two different colours of particles are used. By starting with two emulsions which are bridged, each stabilised by a different colour of particle, and then using confocal microscopy to study them as they are mixed together and deaggregate, the processes involved in deaggregation can be elucidated. These experiments have also shown, for the first time, the dynamic nature of particles in Pickering emulsions; particles transfer readily between droplets when the samples are placed on a roller bank. It is found that a period of unbridging and rebridging takes place prior to deaggregation of the emulsions, and the timescale of deaggregation can be tuned by varying the particle wettability. The two-colour method has also been applied to the study of Pickering emulsions which are repeatedly sheared. It is found that limited coalescence is not reestablished simply by re-applying the shear rate which was used in the initial emulsification. This behaviour is attributed to the presence of an elastic shell of particles at the interface, which inhibits droplet breakup, and is in contrast to that of surfactant-stabilised emulsions, where increasing the stabiliser concentration makes droplets more liable to deform and breakup. Finally, a short study has been carried out attempting to increase the scale of the experiments presented in this thesis to sample volumes of approximately one litre. This study has demonstrated the relevance of particle bridging to industrial emulsification processes. Overall, experiments with carefully controlled model Pickering emulsions, including those using two colours of particles, have revealed the fundamental workings of these arrested systems.

This thesis is an exploratory study of nanomaterials stabilized Pickering emulsions and their applications. The study illustrates some novel emulsion behaviour through dynamic observation and develops a mechanically switchable emulsion based on the microstructure design of nanomaterials. The droplets of emulsion are demonstrated as an effective microreactor for chemical reactions that happen at the oil-water interface, showing the potential application of Pickering emulsion in catalysis.

Stimulus-responsive colloidosomes which completely dissolve upon a mild pH change are developed. pH-Responsive nanoparticles that dissolve upon a mild pH increase are synthesized by a nanoprecipitation method and are used as stabilizers for a double water-in-oil-in-water Pickering emulsion. These emulsions serve as templates for the production of pH-responsive colloidosomes. Removal of the middle oil phase produces water-core colloidosomes that have a shell made of pH-responsive nanoparticles, which rapidly dissolve above pH 7. The permeability of these capsules is assessed by FRAP, whereby the diffusion of a fluorescent tracer through the capsule shell is monitored. Three methods for tuning the permeability of the pH-responsive colloidosomes were developed: ethanol consolidation, layer-by-layer assembly and the generation of PLGA-pH-responsive nanoparticle hybrid colloidosomes. The resulting colloidosomes have different responses to the pH stimulus, as well as different pre-release permeability values. Additionally, fundamental studies regarding the role of particle surface roughness on Pickering emulsification are also shown. The pH-responsive nanoparticles were used as a coating for larger silica particles, producing rough raspberry-like particles. Partial dissolution of the nanoparticle coating allows tuning of the substrate surface roughness while retaining the same surface chemistry. The results obtained show that surface roughness increases the emulsion stability of decane-water systems (to almost twice), but only up to a certain point, where extremely rough particles produced less stable emulsions presumably due to a Cassie-Baxter wetting regime. Additionally, in an octanol-water system, surface roughness was shown to affect the type of emulsion generated. These results are of exceptional importance since they are the first controlled experimental evidence regarding the role of particle surface roughness on Pickering emulsification, thus clarifying some conflicting ideas that exist regarding this issue.

Les émulsions eau/eau (W/W) ont suscité un grand intérêt en raison de leur potentiel d'application dans différentes industries telles que l'agroalimentaire, les produits pharmaceutiques, les cosmétiques et les soins personnels. Le caractère particulier des émulsions W/W est leur stabilisation par ajout de particules. L’objectif de ce travail de thèse est de comprendre cet aspect en étudiant une émulsion modèle W/W à base de dextran et du poly(oxyde d'éthylène) stabilisée par des particules à base de protéines du lactosérum. Dans un premier temps, nous avons étudié l'effet de la morphologie des particules protéiques et leur partitionnement sur la stabilité des émulsions W/W. En particulier, la stabilité s’est révélée dépendre de la structure des particules quand ses derniers étaient sous forme de microgels, d’agrégats fractals ou de fibrilles. Il a été montré que la stabilité s'améliorait lorsque les particules se localiser préférentiellement dans la phase continue. Deuxièmement, nous avons étudié la gélification, des microgels et des agrégats fractals, induite en réduisant le pH entre 6,5 et 3,5 ou en ajoutant 0,3 M NaCl à pH 7,0 aussi bien quand l’excès des particules se situe dans la phase continue ou dispersée. Dans le premier cas, un réseau se formé dans la phase continue de dextran, permettant d’inhiber le crémage des gouttelettes de PEO, les agrégats fractals étant plus efficaces que les microgels. Dans le second cas, des particules protéiques denses pourraient être formées par gélification des gouttelettes de dextran dispersées. Finalement, nous avons exploré l'adsorption des protéines natives sur les particules de latex et leur capacité à stabiliser les émulsions
Water/water (W/W) emulsions have attracted great interest recently due to their high potential for applications in different industries such as food and beverages, pharmaceutical, cosmetics and personal care. An important issue is the stabilization of W/W emulsions by adding particles. The aim of the research for this thesis was to shed light on this issue by studying a model W/W emulsion formed by mixing dextran and poly(ethylene oxide) with particles based on whey proteins. Firstly, we studied the effect of the morphology of protein particles and their partitioning on the stability of W/W emulsions. The stability was different when microgels, fractal aggregates or fibrils were added. We showed that stability improved when the particles partitioned to the continuous phase. Secondly, we investigated gelation of the fractal aggregates and microgels induced by reducing the pH between 6.5 and 3.5 or by adding 0.3M NaCl at pH 7.0 with excess particles either in the continuous or he dispersed phase. In the first case, a network was formed in the continuous dextran phase, making it possible to arrest creaming of PEO droplets, fractal aggregates being more effective than microgels. In the second case, dense protein particles could be formed by gelation of the dispersed dextran droplets. Thirdly, we explored the effect of adsorbing native proteins unto latex particles on their capacity to stabilize W/W emulsions

Les émulsions fluorées de Pickering sont étudiées et mises au point dans la technologie demicrofluidique en gouttes pour des applications d’études sur des cellules adhérentes isolées.Les principaux résultats de ce projet sont : l’établissement d’un lien entre la couverture desurface des nanoparticules et la fluidité de l’émulsion de Pickering ; l’établissement deslignes directrices pour la stabilisation des gouttes avec un débit de production élevé et unminimum de déchets de particules ; et la mise en oeuvre d’une plateforme technologiquecomplète pour l’étude des cellules RPE, pour mesurer leur hétérogénéité phénotypique auniveau de la cellule individuelle
Fluorinated Pickering emulsions are studied and engineered within droplet-based microfluidicstechnology for adherent-cell studies applications. The main findings of this projectinclude: linking the nanoparticles surface coverage to the bulk flowability of the Pickeringemulsion; deriving guidelines for droplet stabilization with high production throughput andminimal particle waste; and implementing the full technological platform for the study ofRPE cells, while unraveling their phenotypic heterogeneity at the single cell level

Mestrado em Ciências e Engenharia de Materiais
Cork material have a very unique set of mechanical and physical properties especially high energy absorption, high friction, low acoustic and thermal conduction, good hydrophobicity and low density. These properties are strongly related to the chemical composition of cork, as well as its honeycomblike microstructure. In this study, inspired by these unique features, we have developed novel high performance bio-foams. Additionally, due to the urgent need to develop concomitantly sustainable materials and green processes, these novel foams were prepared using environment friendly approaches. In this study novel bio-foams mimicking cork were prepared by Pickering emulsion polymerisation of acrylated epoxydised soybean oil (AESO) using acetylated bacterial cellulose (Ac-BC) as an emulsion stabiliser. Following more closely cork structure and chemical composition, additional sustainable foams composed of higher concentrations of Ac-BC, were prepared. Also, the first steps towards the incorporation of lignin-like compounds in these foams were done. Both emulsions and ensuing foams were exhaustively characterised by means of several techniques, viz., SEM, optical microscopy, TGA, DMTA, FTIR, among others. The stabilisation of a 70% high internal phase water-in-AESO emulsion (HIPE) was verified. The cellular structure of the novel foams was confirmed by SEM analysis. It was found that depending on the ratio between water/oil we could tune pore dimensions and density, and hence to approach more closely cork microstructure. Moreover, the new foams thermal properties, especially in terms of thermal stability, were found to be close to cork behaviour. Furthermore, the mechanical properties of the foams were studied by DMTA, and the glass transition value was found to be between 30-60 oC.
A cortiça tem propriedades mecânicas e físicas únicas, em particular uma elevada capacidade de absorção de energia, elevada fricção, baixa condução acústica e térmica, elevada hidrofobicidade e baixa densidade. Estas propriedades estão relacionadas tanto com a sua composição química como com a sua microestrutura. Neste estudo, inspirado por estas características e morfologia únicas da cortiça, desenvolveram-se novas espumas de origem renovável com elevado desempenho. Adicionalmente, devido à necessidade premente em desenvolver concomitantemente materiais sustentáveis e processos verdes, estas novas bio-espumas foram preparadas seguindo abordagens amigas do ambiente. Em concreto, elas foram preparadas por polimerização em emulsão de Pickering de óleo de soja epoxidado acrilatado (AESO) usando celulose bacteriana acetilada como estabilizante da emulsão. Adicionalmente, seguindo mais de perto a microstrura e composição da cortiça, prepararam-se espumas sustentáveis contendo concentrações elevadas de celulose e foram dados os primeiros passos no sentido destas espumas incorporarem compostos semelhantes à lenhina. As diversas emulsões preparadas bem como as espumas resultantes foram caracterizadas detalhadamente através de várias técnicas, tais como SEM, microscopia óptica, TGA, DMTA, FTIR, estre outras. Verificou-se que a composição ótima da emulsão água-em-AESO foi estabilizada com 70% de água o que corresponde a uma emulsão do tipo ‘High Internal Phase Emulsion’ (HIPE). A microestrutura celular das novas bio-espumas foi confirmada por SEM, verificado que dependendo da composição inicial das emulsões (rácio água/óleo) pode-se controlar as dimensões e densidades dos poros e assim ajustar a porosidade à da cortiça. Estudou-se o comportamento térmico das espumas via TGA, podendo-se concluir que elas têm um comportamento semelhante à cortiça. É ainda de realçar que em termos de análise por DMTA, verificou-se que a temperatura de transição vítrea varia entre 30-60 oC.

The thesis constitutes an investigation into the production of floating photocatalytic particles (FPP) as a low cost, low carbon footprint and chemical-free wastewater treatment. It is anticipated that this approach would be particularly attractive for developing countries where it could reduce incidences of disease and pollution. The particles were manufactured from cocoa butter (CB), and contained either photocatalytic nanoparticle titanium dioxide TiO2 (P25) or silver-doped TiO2 (0.5% w/w). The photocatalytic activity of the particles was evaluated by means of the decolourisation of the dye indigo carmine (IC). Three arrangements were used; small scale treatment using Petri dishes, an 1800 ml batch-recirculation photoreactor and an 8 litre UV contactor. Membrane emulsification (ME) was the technique used here to generate particles of controlled size. The particles were in effect what are known as Pickering emulsions in which the solid fat core (CB) was stabilised by TiO2 nanoparticles, resulting in composite particles that float easily and can receive incident light to generate highly reactive free radical species. The FPPs were characterised by FEGSEM and EDs mapping analysis, and the images obtained displayed a spherical structure with a rough outer surface, and the EDs showed a good coverage of TiO2 on the surface of at a maximum loading of 10% w/w. Tests were conducted to assess the stability of the particles when used in repeated cycles. Reuse of the particles caused a significant drop of photodegradation activity after four cycles to 42% of that of freshly prepared particles. The correlation of photocatalytic activity with silver dosage was also investigated. The highest photocatalytic activity was achieved at 0.5 wt. % of silver doped TiO2 and was some 10% greater than for un- doped particles. The organic carbon release resulted from TOC analysis for the FPPs that were exposed to UV light for 8.5 hr in water was less than 1 wt. %. First order reaction kinetics were exhibited during decolourisation of IC dye with respect to the initial dye concentration, radiation intensity, percentage coverage of the liquid surface by the FPPs, and the catalytic loading. For a static system (i.e. no forced convection), the most effective surface coverage was identified as being in the range of 60 to 80%. A linear source spherical emission model (LSSE) was adopted to estimate the intensity of the incident radiation on the surface of the FPP layer in the photoreactor and validated. In addition, a preliminary kinetic model to describe of the effect of the photocatalytic active surface concentration of TiO2 as well as the efficient intensity flux in the kinetic model was developed for the FPP layer photoreactor.

La valorisation de la biomasse pour des applications de haute valeur ajoutée est un véritable défi scientifique, technologique et environnemental. Valoriser le bois et stimuler son usage industriel vers des applications durables est un enjeu climatique : le bois et la forêt sont des puits de carbone. Les fonctionnalités natives du bois lui confèrent des propriétés hydrophiles et hydrophobes pour se placer aux interfaces et stabiliser des émulsions. Ces recherches constituent donc une réponse aux questions de substitution de surfactifs issus de la pétrochimie par des matériaux naturels, renouvelables et biodégradables. Des études multiparamètres ont permis de comparer l’efficacité d’émulsification et de stabilisation d’émulsions en fonction des paramètres de procédé (technologie Ultra-Turrax UT, technologie Ultra-Sons US), et de formulation. Des émulsions stables sont générées à partir de dépenses énergétiques qui dépendent de la technologie mise en place (3000 kJ.L-1 par sonde à US et 6000 kJ.L-1 par UT). En formulation, des bornes ont été déterminées, en concentration en particules (0,31 g.L-1 à 2,37 g.L-1), en fraction volumique d’huile (0,1 à 0,6), en pH (3 à 9) et en salinité (< 2 g.L-1) pour délimiter les zones de meilleure stabilité des émulsions directes et utiles pour des changements d’échelles de travail (> TRL 4). Des voies de modification des propriétés de surface des particules de bois ont été abordées pour obtenir des émulsions inverses et multiples. Les particules de bois sont des nouveaux candidats performants pour la stabilisation des émulsions
The valorization of biomass for high value-added applications is a real scientific, technological and environmental challenge. Valuing wood and stimulating its industrial use towards sustainable applications is a climatic issue: wood and the forest are carbon sinks. The native features of the wood give it hydrophilic and hydrophobic properties for interfacing and stabilizing emulsions. This research is therefore an answer to the question of substitution of surfactants from petrochemicals by natural, renewable and biodegradable materials. Multiparameter studies have made it possible to compare the emulsification and emulsion stabilization efficiency as a function of process (Ultra-Turrax UT technology, Ultra-Sound US technology) and formulation parameters. Stable emulsions are generated from energy expenditure that depends on the technology implemented (3000 kJ.L-1 for the US probe and 6000 kJ.L-1 for UT). In formulation, limits were determined, in particle concentration (0,31 g.L-1 to 2,37 g.L-1), in volume fraction of oil (0,1 to 0,6), in pH (3 to 9) and in salinity (< 2 g.L-1) to delimit zones of better stability of direct emulsions, useful for upscaling studies (> TRL 4). Pathways for modifying the surface properties of wood particles have been addressed to obtain inverse and multiple emulsions. Wood particles are new and powerful candidates for the stabilization of emulsion

Cellulose nanocrystals (CNCs) are bio-based nanoparticles with the ability to stabilize oil and water emulsions thanks to their intermediate wettability and nanometric size. These and other types of particle-stabilized emulsions, commonly referred to as Pickering emulsions, are of great academic and industrial interest due to their superior stability against drop coalescence compared to classical surfactant-stabilized emulsions. In addition, the presence of a densely packed layer of particles at the oil-water interface is expected to impact the encapsulation ability of the emulsion droplets opening up for the possibility to use these systems to modulate the release of active substances in the context of oral or topical delivery formulations used in pharmaceutical and cosmetic applications. In these types of applications, the use of emulsions with nano-sized drops is advantageous due to their longtermcolloidal stability, improved dermal and mucosal transport of actives, improved bioavailability and greater aesthetic appeal and skin feel. This study had two main objectives. The first one was to explore to possibility to produce o/w emulsions with submicron-size drops by means of microfluidization using a combination of CNCs and hydroxypropyl methylcellulose (HPMC), a surface-active cellulose derivative that has been shown to have the ability to modify the wettability of CNCs (thereby enhancing their ability to adsorb at the oil/water interface). An important aspect of this first part of the study also involved gaining better understanding on the separate contributions of CNCs and HPMC to the properties of the resulting emulsions. The second objective of the work was to assess the performance of selected o/w CNC/HPMC compared to that of surfactant-stabilised emulsions in terms of their ability to deliver lutein, a hydrophobic prototype active of interest for topical delivery applications.
Cellulosa-nanokristaller (CNC) är biobaserade nanopartiklar med förmågan att stabilisera emulsioner av olja i vatten (o/w) tack vare deras medelhöga vätbarhet och storlek i nanometerskalan. Dessa och andra typer av partikelstabiliserade emulsioner, så kallade Pickering-emulsioner, är av stort akademiskt och industriellt intresse på grund av deras överlägsna stabilitet mot droppkoalescens jämfört med klassiska tensidstabiliserade emulsioner. Det tätt packade skiktet av partiklar vid gränsytan mellan olja och vatten påverkar också inkapslingsförmågan hos emulsionsdropparna vilket kan utnyttjas för att reglera frisättning av aktiva substanser i läkemedel eller kosmetiska produkter. I dessa typer av applikationer är användningen av emulsioner med droppar i nano-storlek fördelaktig på grund av deras långsiktiga kolloidala stabilitet, förbättrad hud- och slemhinnetransport, förbättrad biotillgänglighet och hudkänsla. Denna studie hade två huvudmål. Det första var att undersöka möjligheten att producera o/w emulsioner med droppar av submikron-storlek med hjälp av mikrofluidisering och genom att använda en kombination av CNC och hydroxypropylmetylcellulosa (HPMC), ett ytaktivt cellulosa-derivat som har visat sig ha förmågan att modifiera vätbarheten hos CNC och därigenom förbättra dess förmåga att adsorbera vid olja/vatten-gränsytan. En viktig aspekt av denna första del av studien var att få bättre förståelse för hur CNC och HPMC var för sig påverkar egenskaperna hos emulsionerna. Det andra målet med arbetet var att bedöma prestandan hos o/w CNC/HPMC-emulsioner för frisättning av lutein, ett hydrofob aktivt ämne, och jämföra med tensidstabiliserade emulsioner.
nanocellulosa, hydroxipropylmetylcellulosa, Pickering emulsioner, microfluidization, drogleverans

The interfaces of bubbles and droplets imbue foams and emulsions with extraordinary mechanical and chemical properties. The remarkably large interfacial area of these structures controls their thermodynamics and makes them practical and functional materials. When these interfaces are forced to touch, they can turn a dispersion of one fluid in another into a solid. These solid-like properties are evident in common household products such as shaving foam and mayonnaise, and our ability to control the fluid and solid properties of these materials is essential to their function.
Physics

This thesis investigates montmorillonite clay particles, which are plate-like and have a hydrophilic surface, a high surface charge and a high specific area. Four studies were carried out and new results relating to polyetheramine adsorption on clay, clay suspension structure and clay-stabilised emulsions are reported. Protonated amines are known to adsorb to clay due to charge interactions. However the adsorption of polymers with primary amine end group at high pH has not previously been studied. We carry out the first such study on the adsorption of polyetheramines at a pH higher than the pKa of the amines. Our results reveal that the adsorption happens via an ion-exchange mechanism. In the adsorption process, the primary amine end-groups get protonated and release hydroxyl ions. The adsorbed molecules adopt a touching mushroom configuration. The effect of the polyetheramine adsorption on the suspension was initially observed due to the obvious change of suspension viscosity. At full coverage of the polyetherarnine, rheological data reveal that the sol/gel transition of the suspension is shifted from 3wt% to 6 wt% clay. Using scattering techniques, large scale string-like structures are found in the bare clay suspensions, which subsequently disappear upon the addition of polyetheramine. This thesis also includes the study of clay particles at interfaces. Surface-modified clay particles are found to stabilise oil-in-water Pickering emulsions. The clay particles at the droplet surface are found to adopt an orientation parallel to the droplet surface, and there are on average four layers of clay particles at the interface. Using Pickering emulsions as a template, well-defined clay microcapsules were prepared by cross-linking the clay particles at the droplet surface. The conclusion on clay orientation is further substantiated by direct observation of the microcapsule surface using SEM.

[ES] El proceso de emulsificación de aceites ricos en compuestos bioactivos permite su mejor aplicación y conservación durante el tiempo de almacenamiento. Entre los diversos mecanismos de emulsificación, se destaca el método de Pickering ya que utiliza nanopartículas sólidas naturales en sustitución de los tensioactivos artificiales. Debido a sus propiedades antioxidantes, no toxicidad y disponibilidad, en este trabajo se estudiaron distintas modificaciones del quitosano para su potencial aplicación como partícula de Pickering. Las modificaciones estudiadas fueron la autoagregación, también denominada desprotonación, y el entrecruzamiento con tripolifosfato de sodio. Se evaluó el comportamiento de estas partículas emulsionando aceite de café tostado, un subproducto de la industria de café con un alto contenido de compuestos bioactivos y compuestos volátiles de interés. Posteriormente, se analizaron las propiedades físico-químicas y la estabilidad de las microcápsulas producidas tras el secado de las emulsiones mediante técnicas de secado por atomización y liofilización. Todas las emulsiones se caracterizaron por tener un comportamiento reológico pseudoplástico, sufriendo desintegración a lo largo del proceso de digestión. Las emulsiones formuladas con nanopartículas de quitosano desprotonadas y menor concentración de aceite mostraron una mejor estabilización y, en consecuencia, una mayor bioaccesibilidad de los compuestos fenólicos totales. Las diferentes nanopartículas de quitosano se caracterizaron estudiando su carga superficial, distribución del tamaño de partícula, microestructura y afinidad agua/aceite. A medida que se aumentó la concentración de estas partículas, se afectó positivamente la viscosidad de las emulsiones debido a la formación de una red tridimensional en la fase continua. Las nanopartículas obtenidas al entrecruzar quitosano con tripolifosfato de sodio fueron más pequeñas, dando como resultado emulsiones con gotas más pequeñas. Las emulsiones de Pickering que contenían un 10% de aceite de café tostado se secaron por atomización y se liofilizaron utilizando las diferentes nanopartículas de quitosano estudiadas y maltodextrina como agentes portadores. Las microcápsulas obtenidas tuvieron la humedad, actividad del agua y solubilidad adecuada para su manipulación y almacenamiento. La presencia de nanopartículas de quitosano permitió una mayor retención de aceite en las microcápsulas y mayor eficiencia de encapsulación. Los compuestos bioactivos y las propiedades antioxidantes se conservaron mejor durante la liofilización. Por otro lado, las microcápsulas obtenidas por atomización presentaron mayor protección de estos compuestos durante la digestión. Las microcápsulas formuladas con nanopartículas desprotonadas fueron sometidas a almacenamiento durante 30 días a 25 ºC. Durante el almacenamiento, se evaluó la protección contra la oxidación de lípidos y la liberación de volátiles. Las isotermas de sorción de agua de estas muestras se determinaron también previamente en las condiciones de almacenamiento. Ambas muestras presentaron isotermas del tipo II, lo que permitió un buen ajuste del modelo de GAB a los datos experimentales. La determinación del índice de peróxido y del contenido de dienos conjugados dio lugar a valores adecuados durante el almacenamiento, aunque las muestras liofilizadas presentaron una ligera tendencia a la oxidación debido a la mayor cantidad de aceite superficial. Aunque hubo ligeras diferencias entre las muestras secas, todas mostraron menos pérdida de aromas totales (~28%) en comparación con el aceite no encapsulado (~51%) al final del almacenamiento. Así, se concluyó que las nanopartículas de quitosano estudiadas fueron eficientes para encapsular el aceite de café tostado y preservar sus características frente a la acción de agentes externos.
[CA] El procés d'emulsificació d'olis rics en compostos bioactius permet la seua millor aplicació i conservació durant el temps d'emmagatzematge. Entre els diversos mecanismes d'emulsificació, destaca el mètode de Pickering, ja que utilitza nanopartícules sòlides naturals en substitució als tensioactius artificials. A causa de la seua propietat antioxidant, de la no toxicitat i de la disponibilitat, aquest treball va buscar analitzar el quitosà i les seues modificacions com potencials partícules de Pickering. Les modificacions estudiades van ser la autoagregació, també anomenada desprotonació, i l'entrecreuament amb tripolifosfat de sodi. Es va avaluar el comportament d'aquestes partícules emulsionant oli de cafè torrat, un subproducte de la indústria del cafè amb un alt contingut de compostos bioactius i volàtils d'interès. Posteriorment, es van analitzar les propietats fisicoquímiques i l'estabilitat de les microcàpsules produïdes després de l'assecat de les emulsions mitjançant tècniques d'assecatge per atomització i liofilització. Totes les emulsions tenien un comportament reològic pseudoplàstic, sofrint desintegració al llarg del procés de digestió. Les emulsions formulades amb nanopartícules de quitosà desprotonades i menor concentració d'oli van mostrar una millor estabilització i, en conseqüència, una major bioaccesibilitat als compostos fenòlics totals. Les diferents nanopartícules de quitosà es van caracteritzar estudiant la seua càrrega superficial, distribució del tamany de partícula, microestructura i afinitat aigua/oli. A mesura que es va augmentar la concentració d'aquestes partícules, es va afectar positivament la viscositat de les emulsions a causa de la formació d'una xarxa tridimensional en la fase contínua. Les nanopartícules obtingudes a l'entrecreuar quitosà amb tripolifosfat de sodi van ser més menudes, donant com a resultat emulsions amb gotes més menudes també. Les emulsions de Pickering que contenien un 10% d'oli de cafè torrat es van assecar per atomització i es liofilitzaren utilitzant les diferents nanopartícules de quitosà estudiades i maltodextrina com a agents portadors. Les microcàpsules obtingudes van obtenir una humitat, activitat de l'aigua i solubilitat adequada per a la seua manipulació i emmagatzematge. La presència de nanopartícules de quitosà va permetre major retenció d'oli en les microcàpsules i major eficiència d'encapsulació. Els compostos bioactius i les propietats antioxidants es van conservar millor durant la liofilització. D'altra banda, les microcàpsules obtingudes per atomització presentaren major protecció d'aquests compostos durant la digestió. Les microcàpsules formulades amb nanopartícules desprotonades també van ser sotmeses a la prova d'emmagatzematge durant 30 dies a 25°C. Durant l'emmagatzematge, es va avaluar la seua protecció contra l'oxidació de lípids i l'alliberament de volàtils. Per això, les isotermes de sorció d'aigua d'aquestes mostres es van determinar prèviament en les condicions d'emmagatzematge. Les dues mostres van presentar isotermes de tipus II, el que va permetre un bon ajust del model de GAB a les dades experimentals. L'índex de peròxids i el contingut de diens conjugats van resultar en valors adequats durant l'emmagatzematge, encara que les mostres liofilitzades van presentar una lleugera tendència a l'oxidació a causa de la major quantitat d'oli superficial. Encara que va haver lleugeres diferències entre les mostres seques, totes van mostrar menys pèrdua d'aromes totals (~28%) en comparació amb l'oli no encapsulat (~51%) a la fi de l'emmagatzematge. Així, es va concloure que les nanopartícules de quitosà estudiades van ser eficients per encapsular l'oli de cafè torrat i preservar les seues característiques enfront de l'acció d'agents externs.
[EN] The emulsification process of bioactive-rich oils makes possible their better application and preservation over the storage time. Among the many emulsification mechanisms, the Pickering method has been highlighted as it uses natural solid nanoparticles in replacement of artificial surfactants. Due to the antioxidant properties, non-toxicity and availability, this work aimed at studying chitosan modifications to produce potential Pickering particles. The studied modifications comprised self-aggregation, also called deprotonation, and crosslinking with sodium tripolyphosphate. The performance of these particles was evaluated in the emulsification of roasted coffee oil, a by-product of the coffee industry with a high content of bioactive and volatile compounds of interest. Subsequently, the physicochemical properties and stability of the microcapsules produced after drying the emulsions using spray-drying and lyophilization techniques were analyzed. All emulsions were characterized as shear-thinning, being them destabilized over the digestion process. Emulsions formulated with deprotonated chitosan nanoparticles and lower oil concentrations showed better stabilization and, consequently, greater bioaccessibility of total phenolic compounds. The different chitosan nanoparticles were characterized regarding surface charge, particle size distribution, microstructure and oil/water affinity. Deprotonated chitosan nanoparticles had a larger particle size, which resulted in emulsions with larger oil droplets. As the concentration of these particles increased, the viscosity of the emulsions was positively affected by the formation of a three-dimensional network in the continuous phase. The nanoparticles obtained by crosslinking with sodium tripolyphosphate were smaller, resulting in emulsions with smaller droplets. The viscosity of these emulsions was lower and little affected by the concentration of particles. Pickering emulsions containing 10% roasted coffee oil were spray-dried and freeze-dried, using the different studied chitosan nanoparticles and maltodextrin as carrier agents. The resulting microcapsules showed adequate moisture content, water activity and solubility for subsequent handling and storage. The presence of chitosan nanoparticles resulted in greater oil retention in the microcapsules and higher encapsulation efficiency. Microcapsules obtained by spray-drying had a more regular spherical shape, while the microparticles obtained by freeze-drying were larger with irregular morphology. Bioactive compounds and antioxidant properties were more preserved during freeze-drying. On the other hand, spray drying allowed greater protection of these compounds during the in vitro digestion. The spray- and freeze-dried microcapsules formulated with deprotonated nanoparticles were subjected to the storage test for 30 days at 25 ºC. During storage, their protection against lipid oxidation and volatile release were evaluated. The water sorption isotherms of these samples were previously determined under the storage conditions. Both samples presented type II isotherms, which resulted in a good fitting accuracy of the GAB model to the experimental data. The peroxide index and the conjugated dienes content resulted in adequate values during storage, although the freeze-dried samples showed a slightly higher tendency to oxidation due to the higher amount of surface oil. Although slight differences were observed between the dried samples, both of them showed less loss of total volatile compounds (~28%) when compared to the non-encapsulated oil (~51%) at the end of storage. Thus, it was concluded that the studied chitosan nanoparticles were efficient to encapsulate roasted coffee oil and to preserve its characteristics against the action of external agents.
The authors would like to thank the project RTI-2018-099738-B-C22 from the ‘Ministerio de Ciencia, Innovación y Universidades’, the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) - (Finance Code 001; Grant number 88887.468140/2019-00) and the São Paulo Research Foundation (FAPESP – Grant number 2016/22727-8) for the financial support.
Franco Ribeiro, E. (2021). Microencapsulation of roasted coffee oil from chitosan nanoparticles-stabilized Pickering emulsions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/163234
TESIS

Bicontinuous Pickering emulsions (or bijels) are a relatively new class of novel soft material with many potential industrial applications, including microfluidics, tissue engineering and catalysis. They are typically formed by initiating the spinodal decomposition of a binary liquid mixture in the presence of neutrally-wetting colloidal particles. The particles attach at the liquid-liquid interface and arrest the phase separation by jamming when the concentration of particles approaches the 2D close-packing limit. Predicted by simulations in 2005 and realized in the laboratory in 2007, many aspects of the bijels complex behaviour and properties have remained unexplored. This thesis expands the knowledge of the bijels structural and dynamical properties, while focusing specifically on the role of particle size. The bijels porosity (average interfacial separation L) according to simulations can be controlled by varying the size r and volume fraction ϕ of particles in the system (L ∝ r/ϕ). The inverse scaling of L with ϕ has been verified for one size of particle, but to access smaller values of L (to allow the structure to be used for a wider range of industrial applications) the scaling with r must be tested. Chapter 3 presents the first systematic study of reducing particle size in bijels made with the liquid pair water/lutidine (W/L).We find that a five-fold reduction in r only requires moderate modification to preparation methods (concentrations of reactants during particle synthesis and increased particle sonication time) and in principle allows L values of between 1 & 10 μm to be accessed in the W/L system, where previously 10 μm was the limit. We demonstrate that this reduced lower bound of L can be translated into a lower bound for polymerized bijels also. Unfortunately, reducing particle size even further (in the same way) reveals a law of diminishing returns, as the uptake fraction of particles to the interface also reduces as we reduce particle size. Hence, to reduce lengthscale even further, a new bijel fabrication paradigm is required. Unexpectedly, we find that the temperature quench rate becomes less important for smaller particles (which constitutes a direct material synthesis advantage) and develop a new theoretical framework to take account of this observation. Large particles promote domain pinch-off during the coarsening (due to a larger driving force towards spontaneous curvature) resulting in bijel failure when slow rates are used because the time required to jam is greater than the time required for depercolation. To further probe the bijels structure as a function of particle size and quench rate, and to account for the success/failure scenarios which seem not to depend on L, in Chapter 4 we quantitatively characterize the morphology by measuring distributions of interfacial curvatures. By computing area-averaged quantities to make valid comparisons, we find that smaller particles and faster quench rates produce bijels with greater hyperbolic `open' character, aligning with our understanding of bijel formation gained from Chapter 3. We compare to simulated bijel data and an estimate of the hyperbolicity of the bare liquids undergoing spinodal decomposition, validating the results. In addition, we uncover a time-dependent `mutation' of the curvature distributions when large particles are used, but not when smaller particles or a different liquid pair is used. The mutation appears to correlate with the propensity of the interfacial particles to form a 'monogel', whereby the interfacial particles develop permanent bonds and remain as a 3D percolating network after the interface is removed, although the precise mechanism of the mutation is still to be verified. Following the results from Chapters 3 & 4 it is clear that there are potentially microscopic phenomena in the bijel which result in macroscopic aging and/or a determination of macroscopic structural properties. To investigate further, we use diffusing-wave spectroscopy (a form of light scattering) to probe the microscopic dynamics of the interfacial particles and/or the particle-laden liquid-liquid (L-L) interface. We find that bijel dynamics show two-step (fast/slow) decay behaviour, with the dynamics slowing as the system ages. The two-step decay is very similar to that observed in colloidal gels formed by diffusion-limited cluster aggregation (DLCA), with the initial (fast) decay due to thermally-activated modes of the gel network, and the later (slow) decay due to the relaxation of internal stresses induced by gel syneresis. For a bijel, the internal stresses could be due to syneresis, but could also be due to the jamming transition and/or the monogelation process and/or the forces acting on the L-L interface by the particle layer. In terms of the aging, if the system does not form a monogel, the correlation functions can be (almost) rescaled on to a master curve, indicating the property of universal aging. If the system does monogel, the functions cannot be superimposed, implicating the monogelation process as a potential cause for a different kind of aging in this system. Due to the interesting differences found when changing the size of the stabilizing particles in a bijel, in Chapter 6 we combine large and small particles (making `bimodal' bijels) and look for evidence of particle segregation by size, quantitatively estimate the ratio of particle uptake fractions and measure kinetics. Larger particles are found to adsorb to the interface in twice the quantity as smaller particles, and we find evidence to suggest the preference of larger particles for interfaces curved in only one direction, corroborating results from previous Chapters. Bimodal bijels take longer to jam than an equivalent monomodal (standard) bijel, which is backed up by simulations and highlights the increased ability of the bimodal particles to reorganise at the interface before arriving at the jammed metastable state. Finally, we also observe that the lengthscale of a bimodal bijel can heavily depend on the quench rate used during the preparation, suggesting that quench rate could be used (as well as particle size, volume fraction and contact angle) as a lengthscale control parameter. This thesis adds to the bijel literature, building on previous experimental studies and verifying/contradicting simulations. Particle size is shown to be a pivotal parameter for bijel formation in the W/L system, with particles of size r = 63 nm proving more versatile (markedly less sensitive to quench rate) than particles of size r ≈ 300 nm. However, even-smaller particles (of the same type) do not provide any additional advantage. We also show how the particle size can not only control bijel porosity (according to L ∝ r/ϕ as predicted by simulations) but can control bijel topology (smaller particles result in structures with greater hyperbolic character). By monitoring the bijel structure over time (topology and dynamics) we have shown that the bijel (in some cases) continues to age for at least c. 1 hr (topology) and in all cases c. 1 day (dynamics). For the first time experimentally, we have used a bimodal dispersion of particles to stabilize a W/L bijel and have uncovered a potentially useful new way to produce samples with different porosities from the same starting mixture, by changing the quench rate. The knowledge of the interplay between particle size and quench rate along with the effect on bijel topology will both assist in the scaling up of processes for industrial-level production and inform future strategies for tailoring the structure for specific applications. Future research should focus on several remaining open questions. The volume fraction of r = 63 nm particles in the W/L system should be increased towards 10% and sonication procedures improved to allow good redispersion to test the lower bound of L, which we expect to be around 1 μm. Also, a new W/L fabrication paradigm should be devised which uses sterically-stabilized particles, to continue the reduction of r towards the value used in simulations (5 nm) in order to test the fundamental physics of bijel formation, specifically what value of interfacial attachment energy is needed for long-term stability. Bijel dynamics can be further probed by using a technique which allows a variation in the probe lengthscale (e.g.
differential dynamic microscopy, DDM), as well as developing a better theoretical model for (multiple) light scattering in a bijel system to arrive at the mechanisms responsible for the anomalous aging, and compare to the predictions of monogelation. Finally, higher magnification/resolution microscopy should be used to look for particle segregation on the liquid-liquid interface (as seen in simulations) and to identify in real-space the locations of the changes in Gaussian curvature over time as measured in Chapter 4.

A novel methacrylate based nanogel system has been designed and developed for drug delivery applications. Methacrylates are optimal tuneable materials in terms of polarity, with combination of hydrophobic and hydrophilic moieties. Synthesis of these nanogels (NGs) was achieved via high dilution radical polymerisation using 2-(tert-butylamino)ethyl methacrylate (tBAEMA) as functional monomer, methacrylic acid (MAA) or ethylene glycol methyl ether methacrylate (EGMMA) as co-monomer and N,N'-methylenebis(acrylamide) (MBA) as cross-linker. Fabricated nanoparticles (NPs) were shown to possess water solubility higher than 2 mg/mL and diameter ranging from 5 to 20 nm (depending on nanogels' composition) as confirmed by either dynamic light scattering (DLS) and transmission electron microscopy (TEM). Moreover, nanogels produced have shown the ability to be employed as Pickering-Ramsden emulsion stabiliser. Their reduced size together with their emulsion capabilities make these nanoparticles a promising system for drug delivery, in particular taking into account skin as administration route. The size is in fact small enough to favour their penetration through the stratum corneum. Furthermore, in the view of their ability to form emulsions, nanogels could be used both as drug carrier and emulsifier in a final pharmaceutical formulation. NGs proved to be able to incorporate both small molecule such as fenoprofen (an anti-inflammatory non-steroidal drug) and big macromolecule such as siRNA. Cytotoxicity and cell metabolism were also evaluated by transfecting normal human dermal fibroblasts (NHDF), keratinocytes (HaCaT) and HeLa cells with nanogels. Data showed that nanoparticles did not affect viability, cells' morphology and adenosine triphosphate (ATP) levels up to high concentration of 100 μg/mL. In addition, preliminary studies indicated the ability of the nanogels to internalise and release their payload inside cells. In conclusion, the results confirmed that this novel system possesses all the desired characteristics to be used as a promising platform for drug delivery.

Dans de nombreux secteurs industriels tels que la production de pigments, de catalyseurs, de produits pharmaceutiques, de minerais ou le recyclage de combustibles nucléaire, les étapes de précipitation et de cristallisation sont cruciales. Bien que ces procédés soient utilisés à grandes échelles avec un contrôle relatif des solides formés, les mécanismes de formation ne sont pas toujours bien compris, en particulier à l’échelle microscopique. Une meilleure compréhension des différentes étapes de formation permettrait d’obtenir des leviers de contrôle adapté à chaque composé et application.Cette thèse se place dans ce cadre très général du contrôle de la précipitation et plus particulièrement de la précipitation en gouttes d’emulsion eau dans l’huile. Deux approches différentes ont été explorées pour moduler et suivre la réactivité dans une goutte d’emulsion. La première approche était basée sur le couplage d’une puce microfluidique générateur de gouttes avec la diffusion de rayons X aux petits angles (SAXS) in situ. Après une caractérisation complète de la compatibilité du polymère non stoechiometrique thiol-ene-epoxy (OSTE+) avec le SAXS, une puce en OSTE+ compatible avec le suivi in situ SAXS a été développée. Un traitement original permettant d’extraire séparément le signal des gouttes du signal de l’huile a permis de valider le montage dans le cas de la précipitation d’oxalate de cerium. La deuxième approche avait pour but l’utilisation de nanotubes d’imogolites pour stabiliser des gouttes d’émulsion et étudier le transport de réactifs entre gouttes via ces nanotubes. Cette approche nécessitait de fonctionnaliser les nanotubes pour les rendre hydrophobe. La caractérisation poussée de la fonctionnalisation des imogolites par des alkylphosphoniques a montré pour la première fois que cette réaction ne conduisait pas à une fonctionnalisation de surface mais à un matériau composite aux propriétés interfaciales remarquables. De nouvelles voies de fonctionnalisation de surface ont été développées pour rendre les imogolites hydrophobes
In the industrial production of pigments, catalysts, plant protection agents, nuclear fuel and pharmaceuticals precipitation and crystallization plays a fundamental role. Although these processes are often applied and a relative control over the formed solids can be achieved, the processes are not always well understood on a microscopic level. To identify how the solids are formed and which mechanisms govern their formation potentially gives the capabilities to better control such processes.In this thesis two different approaches are explored to study precipitation and crystallization by confining reactions into droplets. The first approach focuses on the combination of a droplet microfluidic device and in-situ small angle X-ray scattering. Off-stochiomestry thiol-ene-epoxy polymer is characterized for the use with in-situ X-ray scattering and a protocol is presented to prepare suitable microfluidic devices from this material. An original approach to isolate the scattering signal of the carrier phase and the droplets is then used to study the precipitation of cerium oxalate in droplets. The second approach aims to use imogolite nanotubes to stabilize droplets against coalescence and to study their transport properties to control reactant feeding into droplets. By fully characterizing the necessary surface modification by alkylphosphonic acids for the first time, evidence is found that the reaction does not yield surface modified tubes. Consequentially, new approaches are explored to obtain individually dispersed imogolite nanotubes with a hydrophobic surface

Les émulsions de Pickering ont suscité un intérêt croissant dans de nombreux domaines de la recherche en raison de leur grande stabilité et versatilité. Une attention particulière a été accordée à la fabrication des systèmes complexes et originaux qui peuvent être obtenus avec différentes particules. Cette étude a consisté dans l'analyse des différents paramètres physico-chimiques des particules, des milieux liquides et des systèmes dispersées, et leur relation avec le comportement mécanique et la structure des émulsions afin de prédire et de moduler les caractéristiques de ces dernières. Nous avons étudié plus particulièrement pour la première fois, le diagramme de phase concernant les inversions de phase du type catastrophique et transitionnelle des émulsions de Pickering. Nous avons utilisé des particules de silice avec des structures et hydrophobicités différentes. En particulier, nous avons montré que le mélange de particules de différente hydrophobicités peut moduler finement l'inversion de phase aussi bien que les propriétés rhéologiques et structurales des émulsions. La fabrication de membranes à partir des émulsions de Pickering précédentes a été proposée comme un exemple de l'utilisation de ces systèmes modèles pour la conception de matériaux complexes
Pickering emulsions have gained interest in many fields of research due their properties like higher stability and versatility. Special attention has been given to the processing of complex and original systems which can be obtained by using different particles. This study consists in the analysis of the different physicochemical parameters of particles, liquid media as well dispersion systems, and their relationship with emulsions structural and mechanical behavior in order to predict and modulate the emulsions characteristics. We studied extensively for the first time the phase diagram of catastrophic and transitional phase inversion of Pickering emulsions. We used silica particles with different structure and hydrophobicity. In particular we showed that mixing particles with different hydrophobicity can finely modulate the phase inversion as well the rheological and structural properties of the emulsions. The manufacturing of emulsified membranes based on previous Pickering emulsions was proposed as an example of the use of these systems as templates for the design of complex materials

Les microgels sont des particules colloïdales polymères faiblement réticulées, capables de se gonfler d’un solvant, de se déformer et de s’adsorber à des interfaces liquides. Parmi eux, les microgels de poly(N-isopropylacrylamide) (pNIPAM) sont thermosensibles et présentent une contraction en volume lorsque la température est supérieure à la température de transition de phase volumique, notée VPTT. De précédents travaux ont montré leur capacité à stabiliser des émulsions de Pickering : les émulsions peuvent être stables à des températures inférieures à la VPTT et être déstabilisées sur demande au-dessus de celle-ci. Afin d’approfondir la compréhension du mécanisme de stabilisation des émulsions, nous discutons le rôle de la structure des microgels sur leur adsorption, leur organisation à des interfaces modèles, les propriétés mécaniques des interfaces et les propriétés des émulsions résultantes en terme de stabilité (cinétique, mécanique) et de propriétés d’écoulement. Le rôle de la réticulation, de la présence de charges et de la taille est étudié pour le modèle du pNIPAM. Nous démontrons le lien existant entre conformation et propriétés macroscopiques des émulsions. En prenant en considération à la fois la structure des microgels et les procédés de formulation (voies d’émulsification), des émulsions avec des propriétés rhéologiques et des états de floculation variés peuvent être obtenues. Fort de ces connaissances, les concepts établis à l’aide des microgels de pNIPAM seront généralisés à d’autres familles de microgels, d’une part des systèmes biocompatibles avec des dérivés comportant des chaînes pendantes oligo(éthylène oxyde), d’autre part des microgels sensibles à des stimuli biologiques tels que la reconnaissance de sucre
Microgels are soft and deformable colloidal particles that are swollen by a solvent and display the ability to deform and adsorb at liquid interfaces. The poly(N-isopropylacrylamide) (pNIPAM) microgels are thermo-sensitive and exhibit a volume contraction when the temperature is raised above the volume phase transition temperature (VPTT). These particle have shown high potential as Pickering emulsions stabilizers: emulsions could be stable at ambiant temperature, below the VPTT and destabilize on-demand above it. To get insight into understanding of the emulsion stabilization mechanism, we systematically discuss the relation between the microgel structure, their adsorption, their organization at model interfaces, the viscoelastic behavior of the interface and the resulting emulsions properties in terms of stability and flow behavior. In the present work, using pNIPAM as model microgels, we investigate the effect of their cross-linking density, their size and their charge density. Varying the microgels structures and the formulation conditions (emulsification process), we could control the emulsions flocculation state and rheological behavior. Based on this knowledge, we propose to synthesize new biocompatible microgels as emulsion stabilizers. Using ligand-modified microgels sucrose-sensitive emulsions may be obtained, enlarging the possible application domains

La spécificité des émulsions de Pickering repose sur la présence de particules stabilisantes, substituant l'utilisation de tensio-actifs. Les particules s'adsorbent de manière irréversible aux interfaces des gouttes d'émulsions, leur conférant une stabilité à long terme. L'objectif de cette thèse a été de comprendre, développer et optimiser des procédés permettant la fabrication de différents types d'émulsions de Pickering grâce à des nanoparticules de silice. Trois projets ont vu le jour dans ce travail : (i) Tout d'abord une approche théorique concernant l'étude physico-chimique des interfaces d'émulsions de Pickering stabilisées par des nanoparticules de silice individuelles non- agrégées. L'adsorption de ces nanoparticules sous forme de mono- ou multi- couches aux interfaces des gouttes d'émulsion a pu être mise en évidence en fonction du ratio Huile/Silice intégré au milieu. A haut ratio, le diamètre des gouttes d'émulsion dépend des paramètres de formulation. Des monocouches de nanoparticules peuvent s'adsorber aux interfaces avec un taux de couverture maximal de 54% à la surface des gouttes d'huile. Tandis qu'à bas ratio, le diamètre des gouttes dépend du procédé de fabrication de l'émulsion. Des multicouches de nanoparticules s'adsorbent aux interfaces. (ii) La taille des gouttes d'émulsion a ensuite été réduite par divers procédés afin d'obtenir des nanoémulsions de Pickering, également appelées NanoPickering. La première étape consistait à tester la viabilité de telles émulsions en les fabriquant par un procédé fort en énergie, i.e. la sonication. Dans un second temps un procédé faible en énergie a été utilisé : la nanoprécipitation. Il a ainsi été possible d'obtenir des nanoémulsions de Pickering stables sur plus d'un mois. Cependant, la quantité d'huile maximale incorporable au système final reste faible (environ inférieure à 1wt%). (iii) Une nouvelle application a été développée en parallèle permettant de formuler des émulsions foisonnées de Pickering, intégralement stabilisées par des nanoparticules. Il est possible d'obtenir deux types d'émulsions foisonnées de Pickering : les premières ont une très forte teneur en air ; les secondes sont stables en termes de hauteur grâce à un phénomène de gélification qui a lieu après un changement d'état macroscopique. L'ensemble de ces résultats confirme que les émulsions de Pickering offrent encore à ce jour la possibilité de découvrir de toutes nouvelles applications fabriquées par des procédés innovants. Par exemple, les nanoémulsions sans émulsifiant émulsifiées de manière spontanée, ou encore les émulsions foisonnées intégralement stabilisées sans émulsifiant. De plus, les approches théoriques restent également nombreuses, et les études des phénomènes interfaciaux sont encore des questions scientifiques très actuelles
Pickering emulsions are emulsions stabilized by solid particles in opposition to emulsifiers-stabilized emulsions. The stabilization of Pickering emulsions comes from a strong adsorption of solid particles at the oil-water interface that builds a rigid barrier against coalescence. The aim of this work was to understand, develop and optimize methods for the fabrication of different types of Pickering emulsions stabilized by silica nanoparticles. Three mains axes can be exposed: (i) Firstly, a theoretical approach on the physico-chemical interfacial phenomena of Pickering emulsions stabilized by non-aggregated individual silica nanoparticles. Adsorption as mono- or multi-layers can be reached depending the Oil/Silica ratio. Two behaviors were observed: At high oil/silica mass ratio, the oil/water interface was covered by a monolayer of nonaggregated silica particles. Stable emulsions were stabilized by a monolayer of silica particles at 54% coverage of the oil droplets surface. Oil droplet diameter depends on formulation parameters. Adsorption as multilayers was reached at lower oil/silica mass ratio and oil droplet diameter depends on fabrication process. (ii) Droplets diameters could be reduced thanks to various processes in order to obtain Pickering nanoemulsions, also called NanoPickering. The first step was to test the viability of such emulsions using a high energy process (sonication). Then, a low energy process (nanoprecipitation) was used. Stable Pickering nanoemulsions can be made on more than one month. However, the oil quantity obtained in the final media is low (less than 1wt%). (iii) In parallel, a new application was developed allowing the formulation of Pickering aerated emulsions, totally stabilized by nanoparticles. Two types of Pickering whipped emulsions can be made. One which has high air content or one which has a stable height, thanks to a gelification phenomenon. This occurs after a macroscopic change of state. All of these results confirm that Pickering emulsions offer the opportunity to discover new applications made by innovative processes. For instance, NanoPickering made by spontaneous emulsification, or Pickering whipped emulsion fully stabilized without emulsifiers. Moreover, theoretical approaches and interfacial phenomena studies are still current scientific questions

L'encapsulation peut affecter la digestion et la bioaccessibilité des composés encapsulés, ce qui peut ensuite affecter leur métabolisme. Le but de ce projet était d'étudier les effets de l'encapsulation sur la bioaccessibilité et le métabolisme du DHA, en étudiant une huile de DHA non-encapsulée ou encapsulée, apportée sous forme d'omelette comme matrice alimentaire.L'huile de DHA, composée de triacylglycérols riches en DHA, a été préparée sous forme d'émulsion de Pickering, stabilisée par des isolats de protéines de lactosérum dénaturés par la chaleur. De l'huile pure ou sous forme d’émulsion a ensuite été ajoutée à l’œuf liquide pour obtenir de l’omelette. Les effets de l'encapsulation sur la digestion ont été étudiés à l'aide d'un modèle de digestion statique in vitro pour adulte, puis l’impact sur le métabolisme du DHA a été mesuré sur un modèle rat pris au sevrage.Les résultats ont montré in vitro que l'encapsulation peut augmenter la surface de contact entre l'huile de DHA et les enzymes de digestion, favorisant l'hydrolyse lipasique de l’huile de DHA et améliorant ainsi la bioaccessibilité du DHA. In vivo, l'encapsulation n'a pas impacté le profil global des acides gras, et particulièrement l’accrétion du DHA dans le cerveau. En revanche, le profil des oxylipines, dérivés oxydatifs d’acides gras, a été fortement modifié dans le plasma, le cœur et même le cerveau. Les métabolites dérivés du DHA ont globalement été augmentés tandis que ceux issus des acides gras de la famille n-6 ont été essentiellement atténués.Par conséquent, l'encapsulation de l'huile de DHA pourrait non seulement améliorer la bioaccessibilité du DHA, mais constitue également un facteur clé dans le métabolisme du DHA pour produire des précurseurs de protectines et de maresines, améliorant ainsi le statut de santé global
Encapsulation may affect the digestion and bioaccessibility of the encapsulated bioactive compounds, which in turn affects their metabolism. The purpose of this project was to study the effects of encapsulation on DHA bioaccessibility and metabolism, based on omelet as a food matrix, which contains DHA oil as encapsulated or unencapsulated form.DHA oil composed of DHA-rich triacylglycerols was prepared as a Pickering emulsion, which is stabilized by heat-denatured whey protein isolates. Pure oil or emulsion was then incorporated into eggs and cooked in an omelet. The effects of encapsulation on the digestion and metabolism of DHA were studied by using INFOGEST static in vitro digestion model for adults and in a weanling rat model, respectively.The results showed that encapsulation can increase the contact surface between DHA oil and lipase during the in vitro digestion, thereby promoting the hydrolysis of DHA oil and improving DHA bioaccessibility. In vivo, encapsulation of DHA oil did not modulate the fatty acid profile in tissues, but remarkably modified the oxylipin pattern in plasma, heart and even brain. Specific oxidized metabolites derived from DHA were upgraded while those from n-6 fatty acids were essentially mitigated.Therefore, encapsulation of DHA oil could not only improve the bioaccessibility of DHA, but is also a key factor in the metabolism of DHA to produce protectins and maresins precursors, thereby improving global health status

Die vorliegende Arbeit beschreibt Herstellungsmöglichkeiten für sogenannte Saturn-Partikel. Es handelt sich dabei um Partikel, die auf ihrer Oberfläche drei Bereiche mit unterschiedlichen Eigenschaften aufweisen. Zwei Kappen mit gleichen Eigenschaften sind durch einen Gürtel getrennt, der sich stark von den Kappen unterscheidet. Im Speziellen geht es hier um die unterschiedliche Benetzbarkeit der Bereiche. Die Herstellung von Saturn-Partikeln mit einem hohen Benetzungskontrast wurde auf zwei verschiedenen Wegen realisiert. Als Ausgangspunkt dienten Mikroglaskugeln, die zunächst zur Hydrophobierung ihrer Oberfläche mit einem Silan behandelt wurden. Eine Art der Saturn-Partikel wurde durch das Ätzen eines Gürtels rund um die Partikel mit Flusssäure in einer im Rahmen dieser Arbeit entwickelten Spülzelle erzeugt. Auf diese Weise konnten Partikel mit zwei hydrophoben Kappen und einem hydrophilen Gürtel erhalten werden. Eine weitere Art dieser Partikel wurde durch das Abschleifen der Partikelkappen nach vorheriger Einbettung in Polymerfilme erhalten, wodurch die hydrophobe Beschichtung abgetragen und das ursprünglich hydrophile Glas freigelegt wurde. Die so erhaltenen Partikel wiesen zwei parallele, hydrophile Bereiche auf, die durch einen hydrophoben Gürtel voneinander getrennt waren. Es wird gezeigt, dass Saturn-Partikel in Systemen mit Wasser und Öl beim Mischen von unterschiedlichen Anteilen der drei Phasen durch Selbstorganisationsprozesse verschiedene Strukturen wie Ketten oder Schichten ausbilden können. Des Weiteren sind sie in der Lage in einem System mit Wasser und Luft besondere Schäume auszubilden, die eine sehr hohe Stabilität aufweisen. Die Partikel stabilisieren darin Flüssigkeitsfilme zwischen den Luftblasen, wobei der hydrophile Gürtel im Wasserfilm und die hydrophoben Kappen in der Luft liegen.

Les peintures sont omniprésentes dans nos civilisations modernes et décorent presque tous les supports et ce dans des domaines très variés. L'utilisation massive des peintures pose cependant des problèmes environnementaux et de santé publique, de par la présence de solvants qui, lors du séchage, s'évaporent et émettent des composés organiques volatiles (COV) néfastes pour l'environnement et l'homme. Une démarche européenne et mondiale de réduction d'émission des COV est donc en cours depuis quelques années. De plus, l'engouement croissant pour le développement durable pousse à la transition de produits pétrosourcés vers des produits biosourcés, à coûts et performances similaires. Les résines alkydes en émulsions, développées au début du XXème siècle, constituent une alternative de choix car émettant une quantité limitée de COV et obtenues par polycondensation de matières premières renouvelables. Après un état de l'art sur le contexte des peintures actuelles et la composition d'une peinture alkyde en émulsion, leurs propriétés physiques et chimiques ont été étudiées. Après ce travail de formulation, deux additifs ont été synthétisés afin d'augmenter le taux de biosourcé des peintures alkydes en émulsion : un épaississant et un agent dispersant. De par la présence de surfactants, les formules de peintures alkydes en émulsion sont pour l'heure moins compétitives que les peintures alkydes en phase solvant. En conséquence, la première émulsion alkyde sans tensioactif a été développée et ses performances évaluées en peinture
Paints and coatings occupy a prominent place in the cultural history of mankind. People have always been fascinated by colors and used paints to decorate and beautify themselves and their environment. Nevertheless, these products bring a lot of problems. For instance, some paints still contain organic solvents, which have negative impacts on the environment and human health. Due to environmental legislations and the need to reduce VOCs emission (volatile organic compounds), water-based paints have attracted a lot of interest. Moreover, the raising sustainability awareness is a driving force for the transition from petrobased to biobased products with equivalent costs and performances. In this context, alkyd resin emulsion, introduced in the 1990s, still continue to be the most widely used binder, because they have low VOCs level and are synthesized by polycondensation reactions of renewable raw materials. After reviewing the current state of the art regarding the alkyd paint emulsion, their physical and chemical properties were studied. Two additives, respectively a rheology modifier and a dispersing agent, were also synthesized, in order to increase the biobased content of alkyd paint emulsion Due to the presence of wetting agent, alkyd emulsion paints are still less competitive than solvent-borne alkyd paints. The first surfactant free alkyd emulsion was consequently developed and its film properties characterized in paint formulation

Les travaux de cette thèse portent sur la formation et la polymérisation d'émulsions de Pickering stabilisées par des nanocristaux de cellulose (NCC). Tout d’abord, les NCC sont fonctionnalisés en surface de façon à modifier d'une part, leur balance hydrophile/hydrophobe et d'autre part, apporter des fonctions promoteurs de la polymérisation par ATRP de la phase interne ou externe. A l'aide de ces NCC, des émulsions directes, inverses et doubles de styrène et de monomères acryliques ont été stabilisées puis polymérisées. L'impact, de la fonctionnalisation des NCC, de la nature du monomère et de l’amorceur, de la présence ou pas de sel sur, la taille, la stabilité, la couverture des gouttes et la morphologie des objets obtenus, a été étudiée. Les latex issus de la polymérisation radicalaire d’émulsions directes de Pickering ont permis la préparation de composites aux propriétés mécaniques améliorées par rapport à celles de la matrice sans charge. Les émulsions stabilisées par des NCC réactifs ont conduit à la synthèse de capsules ou de billes pleines en fonctions de la nature du monomère polymérisé. Des matériaux poreux ont été obtenus par polymérisation des émulsions inverses de Pickering. Enfin, la polymérisation des émulsions doubles a permis l’obtention d’objets à morphologie tout à fait inédite avec l’encapsulation de capsules de polystyrène dans des capsules plus volumineuses de ce même polymère
Pickering emulsions are based on amphiphilic particle stabilizers, which adsorb irreversibly at the liquid-liquid interface and form a rigid structure around the droplets. Amongst these particles, biosourced and biorenewable cellulose nanocrystals (CNCs) have demonstrated good performances as Pickering stabilizers for oil in water emulsions. In this thesis, a wide range of emulsions of monomers were stabilized by amphiphilic modified CNCs. These Pickering emulsions subsequently serve as vessel to perform radical polymerization. In a first step, the CNCs are modified to tailor the hydrophobic/hydrophilic balance and are used to efficiently stabilize direct (O/W), inverted (W/O) or double W/O/W Pickering emulsions of monomers. The different emulsions obtained were subsequently polymerized, by thermal radical polymerization or by SI-ATRP. The polymerization of the direct emulsions allowed producing either capsules or filled beads, depending on the monomer used, which we assigned to differences in monomer reactivity. Hence, the method offers the opportunity to tune the morphology of the polymerized spheres (empty or filled), by simply controlling the monomer conversion. The polymerization of the inverted emulsion on the other end, led to the formation of a porous material. The polymerization of the double W/O/W emulsions was also envisaged, leading original morphology such as small empty beads encapsulated into larger capsules

L’objectif de cette étude est de valoriser des coproduits végétaux tout en proposant une alternative biosourcée, économique et performante aux tensioactifs classiques. Des émulsions de type huile-dans-eau sont fabriquées à partir de poudres végétales finement broyées comme seul matériel tensioactif. Les systèmes dispersés qui en résultent, stabilisés par des particules solides, sont des émulsions dites de Pickering. La première partie de ce manuscrit décrit l’influence du procédé d’émulsification (rotorstator en régime turbulent, ultrasons et homogénéisation haute pression) et des paramètres de formulation sur les propriétés d’émulsions stabilisées par de la poudre de cacao. Le rôle des différentes fractions de la poudre est déterminé et le phénomène de coalescence limitée propre aux émulsions de Pickering est étudié. Nous mettons en évidence une évolution structurale des particules (« dépliement ») sous l’effet du cisaillement appliqué lors de l’émulsification, permettant d’augmenter leur performance en tant qu’agents stabilisants. L’influence de la nature végétale est explorée en élargissant l’étude à des poudres de compositions différentes issues de tourteaux de colza et de lupin. La stabilité de ces émulsions face à l’élimination de la phase continue est ensuite évaluée au regard de la technique de séchage, par lyophilisation et atomisation. Des émulsions sèches riches en huile et redispersables dans l’eau sont ainsi obtenues. Enfin, le pouvoir antioxydant des poudres végétales avant et après séchage des émulsions est caractérisé
This study aimed at valorizing vegetal byproducts while offering a bio-sourced, cheap and efficient alternative to conventional surfactants. Oil-in-water emulsions were obtained from finely ground plant powders as the only surfactant material. The resulting dispersed systems, stabilized by solid particles, are so-called Pickering emulsions. The first part of this manuscript describes the influence of the emulsification process (rotor-stator in turbulent regime, sonication and high-pressure homogenization) and of the formulation parameters on the properties of emulsions stabilized by cocoa powder. The role of the different fractions of the powder was determined and a phenomenon characteristic of Pickering emulsions, namely limited coalescence, was identified. We evidenced a structural evolution of the particles ("unwrapping") under the effect of the shear applied during the emulsification process, allowing to increase their performance as stabilizing agents. The influence of the vegetal origin was explored by extending the study to powders deriving from rapeseed and lupin oilcakes. The stability of these emulsions with respect to the elimination of the continuous phase was evaluated using 2 drying techniques, freeze-drying and spray-drying. Dry emulsions rich in oil and redispersable in water were obtained. Finally, the antioxidant properties of vegetable powders before and after the drying process were characterized

Synthèse et étude de nouveaux NHC-Boranes pour leurs propriétés énergétiques et leurs rôles en tant que photo co-amorceurs pour la photopolymérisation en émulsion.Depuis la première synthèse de complexes N-Hétérocycliques Boranes (NHC-Borane) stables en 1993, une étude plus générale de propriétés et réactivité n’a débuté que dans le milieu des années 2000. Les domaines d’applications de ces composés qui sont des paires de Lewis vont de la synthèse organique (agent réducteur, hydroboration de liaisons multiples) en passant par la chimie radicalaire (remplacement de l’hydrure de tributylétain, hydroboration) ou même en tant qu’amorceur ou co-amorceur de polymérisations.L’objet de cette thèse était d’étendre l’application des NHC-Boranes dans deux domaines précis. Un premier axe porte sur les propriétés hypergoliques amenées par leurs structures inédites. Un second est consacré à l’amorçage de réactions de polymérisations en émulsion et l’obtention de particules hybrides sous irradiation visible.Nous avons choisi et synthétisé de nouvelles cibles polyazotées qui ont montré des propriétés énergétiques potentiellement intéressantes pour l’usage de NHC-Boranes en propulsion solide. L’étude mis en évidence des différentes de réactivités en fonction du squelette du carbène utilisé. De plus, un nouveau type de carbène borane pouvant être utilisé dans différents domaines a été synthétisé.Nous avons aussi amélioré la compréhension du système de photoamorçage déjà proposé en polymérisation en émulsion dans le visible. Des points clés, sur la conception du système et du réacteur ont été améliorés. Nous avons aussi pu remplacer le tensioactif utilisé pour proposer la première photopolymérisation en émulsion Pickering. Il en résulte des latex stables, composés de particules hybrides pouvant former des films potentiellement anti-UV. L’excitation dans le visible, pourrait être utilisée dans le but de réduire les coûts énergétiques et même former d’autres particules inédites en évitant la dégradation de composés thermo ou UV-sensibles
Study and synthesis of new NHC-Boranes usable as hypergolic fuels and as photo co-initiators for radical emulsion photopolymerizationsThe first N-Heterocyclic Carbene Borane complex (NHC-Borane) was synthetized in 1993, but we had to wait until the mid-2000s before chemists investigated their properties and reactivity. The applications of NHC-Boranes range from organic chemistry (where they are used as reducing agents or for the hydroboration of multiple bonds) to radical chemistry (as replacement of te tributyltin hydride) and radical polymerizations (initiators and co-initiators). We designed and synthetized new Nitrogen-rich NHC-Boranes. The latter are hypergolic and might serve as fuels for solid propulsion. We managed to synthetize several new classed of NHC-Borane which was or could be used in different fields. We also deepened our understanding of the visible light-induced emulsion polymerization, where the NHC-Boranes serve as co-initiators. We could optimize the process and then replaced the surfactant by an inorganic sol to propose the first Pickering emulsion photopolymerization. Stable latexes of hybrid particles have been generated which might be used as sunscreen films, to reduce the energetic footprint of the reactions and/or to access particles made of heat- or UV-sensitive materials

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Atualmente a crescente demanda do uso de repelentes de insetos tem promovido a pesquisa de produtos mais eficazes e com uma maior durabilidade da ação repelente. O objetivo deste trabalho foi a obtenção de novas nanopartículas com propriedades interfaciais modificadas superficialmente com grupos funcionais catiônicos e polímeros aniônicos, com o intuito de melhorar a estabilidade de emulsões Pickering contendo um princípio ativo, N,N -dimetil-m-toluamida (DEET), comumente utilizado nos repelentes comerciais. A obtenção das nanopartículas incluiu a funcionalização inicial da superfície de nanopartículas de sílica comerciais com grupos amino secundários (R-NH2), seguido da introdução de grupos catiônicos de amônio quaternário (R-NR4 positivo) e posterior complexação eletrostática com polímeros aniônicos (poli(ácido acrílico), PAA, e poli(4-estireno sulfonato de sódio), PSS). As nanopartículas modificadas mostraram boa dispersabilidade em meio aquoso, favorecendo a estabilização de emulsões de tipo óleo em água (O/A). Os melhores resultados dos estudos de estabilidade no tempo das emulsões foram obtidos usando as nanopartículas catiônicas (SiNP-A,G) recobertas com PAA e com a mistura de polímeros (PAA mais PSS). As emulsões Pickering obtidas com as nanopartículas de sílica recobertas com PAA mostraram os melhores resultados na retardação da evaporação do DEET, com potencial uso para liberação lenta deste composto.
Currently the increasing demand for insect repellent use has promoted research into more effective products and a longer repellent action. The objective of this work was to obtain new nanoparticles by surface modification with cationic functional groups and anionic polymers, with the aim of improving the stability of Pickering emulsions containing an active ingredient, N,N -diethyl-m-toluamide (DEET) commonly used in commercial repellents. The preparation of the nanoparticles included initial surface functionalization of commercial silica nanoparticles with secondary amino groups (R-NH2), followed by the introduction of cationic quaternary ammonium groups (R-NR4 positive) and subsequent electrostatic complexation with anionic polymers (poly (acrylic acid), PAA, and poly(sodium 4-styrenesulfonate), PSS). The modified nanoparticles showed good dispersibility in aqueous medium, favoring the stabilization of emulsions oil-in-water (O/W). The best results of the emulsion time stability studies were obtained using cationic silica nanoparticles (SiNP-A,G) covered with PAA and with the polymer mixture (PA plus PSS). The Pickering emulsions obtained with the cationic silica nanoparticles coated with PAA showed the best results in retarding DEET evaporation, with potential use for slow release of this compound.

Ce travail de thèse examine une nouvelle méthode prometteuse pour la dépollution efficace des eaux contaminées par des polluants organiques insolubles de type toluène, 1-méthylnaphtalène, nitrobenzène,…. Cette méthode d’oxydation avancée repose sur la photocatalyse hétérogène dans des émulsions de Pickering. Dans ce type d’émulsions, les tensioactifs stabilisants des gouttelettes huileuses sont remplacés par des nanoparticules solides à propriétés photocatalytiques élevées. Par ailleurs, ces nanoparticules solides doivent remplir les conditions de mouillabilité partielle dans les deux phases aqueuse et huileuse grâce à un équilibre hydrophile-hydrophobe à leur surface. Pour cette raison, le dioxyde de titane (TiO2) anatase a été préparé par la méthode sol-gel puis modifié par fluoration pour obtenir le catalyseur TiO2-F. L’objectif est de formuler des émulsions de Pickering de type huile dans l’eau (H/E) à partir de polluants organiques de faible solubilité dans l’eau. Les catalyseurs synthétisés ont été caractérisés par XRD, BET, SEM, DRS, XPS, et TG-TD-MS. Il a été montré que la fluoration apporte des changements importants dans les propriétés optiques du TiO2 et a amélioré l’équilibre hydrophile/hydrophobe à sa surface de façon significative. Par ailleurs, les résultats obtenus indiquent que des émulsions de Pickering stables peuvent être formulées en utilisant des particules de TiO2 ou TiO2-F de taille nanométrique. Le type et la stabilité des émulsions dépendent de la mouillabilité des nanoparticules stabilisantes évaluées par des mesures d'angle de contact. La mouillabilité des nanoparticules a été trouvée fortement dépendante du type d’huile en raison des contributions de la polarité et des interactions spécifiques avec les polluants. L'étude des émulsions de Pickering par conductivité électrique, microscopie optique et diffusion de la lumière a montré qu'une stabilité élevée a été obtenue dans des conditions de mouillage partiel : angle de contact dans l'eau compris entre 70 et 110°. L’évolution de la taille des gouttelettes d'huiles avec le rapport de masse huile/photocatalyseur a confirmé une forte adsorption des nanoparticules de catalyseur sur les gouttelettes d'huiles. Finalement, les émulsions jugées stables ont été photodégradées sous rayonnement UV. La cinétique de photodégradation des polluants organiques mesurée par HPLC a montré que la dégradation a été intensifiée en utilisant les émulsions de Pickering par rapport aux systèmes non émulsionnés. Ces résultats ont prouvé que l’utilisation des émulsions de Pickering stabilisées par des nanoparticules de dioxyde de titane constituait un moyen efficace et innovateur pour intensifier la dégradation photocatalytique des polluants organiques
This thesis examines a promising new method for the effective depollution of water contaminated by insoluble organic pollutants such as toluene, 1-methylnaphthalene, nitrobenzene, etc. This advanced oxidation method is based on heterogeneous photocatalysis in Pickering emulsions. In this type of emulsion, the stabilizing surfactants of the oily droplets are replaced by solid nanoparticles having high photocatalytic properties. Moreover, these solid nanoparticles must fulfill the conditions of partial wettability in both aqueous and oily phases thanks to a hydrophilic-hydrophobic balance on their surface. For this reason, the titanium dioxide (TiO2) anatase was prepared by the sol-gel method and then modified by fluorination to obtain the TiO2-F catalyst. The objective is to formulate Pickering oil-in-water (O/W) emulsions from organic pollutants of low water solubility. The synthesized catalysts were characterized by XRD, BET, SEM, DRS, XPS, and TG-TD-MS. It has been shown that fluorination brings about important changes in the optical properties of TiO2 (change in band gap) and improves the hydrophilic / hydrophobic balance at its surface significantly. Moreover, the obtained results indicate that stable Pickering emulsions can be formulated using TiO2 or TiO2-F nanoparticles. The type and stability of the emulsions depend on the wettability of the stabilizing nanoparticles evaluated by contact angle measurements. The wettability of the nanoparticles has been found to be highly dependent on the type of oil due to the contributions of polarity and specific interactions with pollutants. The study of Pickering emulsions by electrical conductivity, optical microscopy and light scattering showed that high stability was obtained under partial wetting conditions: contact angle in water between 70 and 110°. The change in the size of the oil droplets with the oil/photocatalyst mass ratio confirmed a strong adsorption of the catalyst nanoparticles on the oil droplets. Finally, the judged stable emulsions were photodegraded under UV radiation. The photodegradation kinetics of organic pollutants measured by HPLC showed that degradation was intensified using Pickering emulsions compared to non-emulsified systems. These results have shown that the use of Pickering emulsions stabilized by titanium dioxide nanoparticles is an effective and innovative way to intensify the photocatalytic degradation of organic pollutants

Dans ce travail de thèse, nous avons préparées des émulsions de Pickering innovantes, stabilisées par des nanoparticules (NP) biocompatibles et biodégradables de poly (acide lactique-co-glycolique) (PLGA), en utilisant du Miglyol comme phase huileuse. Ces systèmes permettent de s’affranchir de l’ajout de tensioactifs synthétiques, utilisés pour stabiliser les émulsions classiques, et qui sont souvent à l’origine d’irritations lors de traitements topiques chroniques. Dans ces émulsions ont été co-encapsulées deux substances actives, la première, un agent immunosuppresseur, dans les NP PLGA, la seconde, un agent anti-inflammatoire, dans les gouttelettes de Miglyol.Dans un premier temps, une étude physicochimique approndie a permis de mieux comprendre les mécanismes de stabilisation de ces émulsions, en fonction du type de NP utilisé. Aussi, l’influence de l’ajout de substances actives a été évaluée sur les structures macroscopique, microscopique et interfaciale des émulsions, mais également sur leur stabilité. Dans un deuxième temps, nous avons démontré que l’ajout de Carbopol, un polymère épaississant, permettait d’améliorer la stabilité, la texture et le pH des émulsions. Enfin, le potentiel thérapeutique d’un tel système à été évalué de manière préliminaire, notamment sa cytotoxicité sur des cultures de kératinocytes, mais aussi son activité immunosuppressive sur des cellules immunitaires activées et leur production de cytokines. Un tel système peut donc s’avérer intéressant pour le traitement de pathologies cutanées chroniques
In this thesis work, we formulated innovative Pickering emulsions, stabilized by biocompatible and biodegradable poly (lactic-co-glycolic acid) nanoparticles (NP), using Miglyol as the oil phase. These systems could be an alternative to conventional emulsions, often stabilized with synthetic surfactants that can be responsible for irritation in particular during long-term topical treatments. Two active pharmaceutical ingredients (API) were successfully co-encapsulated, the first one, an immunosuppressant agent, entrapped in PLGA NP, the second one, an anti-inflammatory agent, incorporated in Miglyol droplets.Firstly, a thorough physicochemical characterization allowed to better understand the stabilization mechanism of these emulsions, depending on the type of NP used. Moreover, the influence of the addition of API was evaluated on the macroscopic, microscopic and interfacial structures of the emulsions, also on their stability. Secondly, we demonstrated that the addition of Carbopol, a thickening agent, improved the stability, texture and pH of emulsions. Finally, the therapeutic potential of such system was investigated through preliminary evaluation of its cytotoxicity on keratinocyte cells, but also its immunosuppressive activity on activated immune cells and their cytokine production. Such a system could be interesting for the treatment of chronical skin diseases

Thermally expandable microspheres are spherical particles around 5-­‐40 µm in size, consisting of a polymeric shell in which a blowing agent has been encapsulated. The microspheres are expanded upon heating, resulting in a particularly low density. Microspheres are therefore suitable to use as light weight filler or as foaming agent. AkzoNobel is world leading in the production of expandable microspheres, which are commercialised under the name Expancel. Sustainability is a great focus at AkzoNobel and two issues that AkzoNobel works with today is to develop products free from chlorine and Me1. The aim with this thesis has been to investigate whether it is possible to produce microspheres free from these chemicals and to see if they can be a more sustainable alternative to one of the existing Expancel grades. In this study, the microspheres have been produced through free radical suspension polymerisation and analysed by measuring mainly the particle size and expansion properties. The polymeric shell was composed of the monomers acrylonitrile, methacrylonitrile, and methyl acrylate. The main focus has been to evaluate the silica-­‐based stabilisation system, which stabilise the monomer droplets during the suspension polymerisation. The stabilisation is possible due to the formation of silica flocs that is adsorbed on the surface of the droplets. It has been investigating how different parameters, e.g. amount of stabiliser or mixing procedure, affects the formation of silica flocs and the stabilisation of monomer droplets. For the silica-­‐based system, it was found that the mixing order, stirring rate, and amount of stabilisers affect the formation of flocs. It was also seen that the amount of stabiliser affect the stabilisation of droplets, and that some stabilisers is more significant than others. Microspheres without chlorine and Me1 have successfully been produced in laboratory scale (50 mL and 1 L). The expansion and size of the microspheres produced in this study was relatively similar to one of the existing Expancel grades. However, the reproducibility of polymerisations in 1 litre reactors has been poor.
Termiskt expanderbara mikrosfärer är sfäriska partiklar, ca 5-­‐40 µm i diameter, som består av ett polymerskal som innesluter en drivgas. Mikrosfärerna expanderar när de utsätts för värme och erhåller då en mycket låg densitet. De är därför lämpliga att använda som fyllmedel då låg vikt är önskvärt eller som skummedel. AkzoNobel är världsledande inom produktion av expanderbara mikrosfärer, som marknadsförs under namnet Expancel. Hållbar utveckling är en viktig fråga för AkzoNobel och två problem som de står inför idag är att utveckla produkter fria från klor och Me1. Målet med detta examensarbete har varit att undersöka om det är möjligt att framställa mikrosfärer fria från dessa kemikalier och om de framtagna mikrosfärerna skulle kunna vare ett hållbarare alternativ till en av de befintliga Expancel-­‐ produkterna. I den här studien har mikrosfärerna framställts genom suspensionspolymerisation som initierats av fria radikaler och de har analyserats främst genom att mäta partikelstorlek och expansionsegenskaper. Polymerskalet bestod av monomererna akrylnitril, metakrylnitril och metylakrylat. I det här arbetet har det viktigaste varit att utvärdera det silikabaserade stabiliseringssystemet som stabiliserar monomerdropparna vid polymerisationen. Stabiliseringen är möjlig eftersom silika bildar flockar som adsorberar på ytan av monomerdropparna. Olika parametrar, exempelvis mängd stabiliseringsmedel och satsningsförfarande, har därför varierats för att undersöka vilken effekt det får på flockningen av silika och stabiliseringen av monomerdroppar. Satsningsordning och omrörningshastiget för stabiliseringssystemet samt mängd stabiliseringsmedel är några av de faktorer som påverkar bildningen av flockar. Det konstaterades även att mängd stabiliseringsmedel påverkar stabiliseringen utav monomerdropparna. Fulländade mikrosfärer utan klor och Me1 har framställts i laboratorieskala (50 mL och 1 L) och partikelstorleken samt expansionsegenskaper är jämförbara med en av Expancels nuvarande produkter. Dock har reproducerbarheten i 1 litersskala varit otillfredsställande.

A produção de filmes biodegradáveis à base de amido representa um desafio tecnológico, pois estas matrizes são altamente sensíveis à água. Neste sentido, as pesquisas estão sendo realizadas a fim de melhorar as caraterísticas de hidrofobicidade sem afetar a integridade estrutural das matrizes. Dentre os compostos comumente empregados para melhorar as características de filmes biodegradáveis, pode-se mencionar os óleos e ácidos graxos. O óleo de sementes de melancia apresenta alto potencial de aplicação em matrizes filmogênicas, pois além da possibilidade de melhorar as propriedades de barreira, apresenta compostos fitoquímicos com atividade antioxidante, que podem conferir um caráter ativo aos materiais produzidos. Neste contexto, o objetivo deste trabalho foi desenvolver e caracterizar filmes à base de amido modificado de mandioca e óleo de sementes de melancia. O óleo de sementes de melancia foi extraído por batelada com etanol pressurizado, sob diferentes temperaturas de extração (40, 60 e 80°C) e diferentes comprimentos de leito de extração (L1 = 4,2 cm, L2 = 9,8 cm e L3 = 15,8 cm). A cinética de extração foi matematicamente descrita utilizando-se o modelo de Peleg e os óleos caraterizados quanto à atividade antioxidante. Posteriormente foram testados quatro amidos modificados de mandioca (amido reticulado, AR; amido acetilado, AA; amido não modificado, ANM e amido duplamente modificado, AAR) com a finalidade de selecionar o que apresentasse melhores caraterísticas na produção de filmes quanto ao caráter hidrofóbico. Os filmes foram produzidos pela técnica de casting, utilizando - se concentrações fixas de amido e sorbitol (4 e 1,2 g/100g de solução filmogênica, respectivamente). O caráter hidrofóbico das matrizes foi avaliado pela determinação da solubilidade, grau de inchamento, permeabilidade ao vapor de água e ângulo de contato. Adicionalmente, foram produzidas emulsões através da técnica de Pickering, com diferentes concentrações de óleo e amido e caraterizadas quanto à estabilidade, tamanho de partículas e polidispersidade. A emulsão com maior estabilidade foi incorporada na formulação de filmes à base de AR em concentrações de 0 a 0,5 g de óleo na emulsão/100 g de solução filmogênica. Todos os filmes foram caracterizados quanto às propriedades mecânicas, microscopia, espectroscopia de infravermelho (FTIR), difração de raios X, cor, solubilidade, inchamento, permeabilidade ao vapor de água e ângulo de contato. Os resultados da extração de óleos mostraram rendimentos superiores sob temperaturas de 80°C e melhor atividade antioxidante a 60°C. O modelo de Peleg apresentou um bom ajuste, observando-se coeficientes de correlação altos (R2 > 0,90). A caraterização dos filmes produzidos com diferentes amidos modificados mostrou que o AR formou matrizes com maior ângulo de contato, menor grau de inchamento e maior resistência mecânica. As emulsões com maior de estabilidade foram produzidas com altas concentrações de óleo e amido (15 e 12 g/100 g de emulsão, respectivamente). Os filmes produzidos com incorporação de óleo na forma de emulsão Pickering apresentaram caráter mais hidrofóbico, sendo também alteradas as caraterísticas estruturais com o aumento da concentração de óleo. Os filmes produzidos com a incorporação de óleo em forma de emulsão apresentaram conteúdos de fenólicos totais de 0,19 a 5,68 mg equivalente de ácido gálico/100g de filmes. No entanto, os filmes não apresentaram atividade antioxidante frente ao radical DPPH•.
The production of biodegradable films based on starch represents a technological challenge because these matrices are highly sensitive to water. In this sense, the research is being carried out in order to improve the characteristics of hydrophobicity without affecting the structural integrity of the matrices. Among the compounds commonly used to improve the characteristics of biodegradable films, the oils and fatty acids can be highlighted. The oil of the watermelon seeds presents high potential of application in filmogenic matrices because in addition to the possibility of improving the barrier properties, it presents phytochemical compounds with antioxidant activity, which can impart an active characteristic to the produced materials. In this context, the objective of this work was to develop and characterize films based on modified cassava starch and watermelon oil. The watermelon oil was extracted in batches with pressurized ethanol under different extraction temperatures (40, 60, and 80°C) and different extraction bed lengths (L1 = 4.2 cm, L2 = 9.8 cm, and L3 = 15.8 cm). The kinetics of extraction were mathematically described using the Peleg model and the oils characterized for antioxidant activity. Four modified starches of cassava (reticulated starch, AR, acetylated starch, AA, unmodified starch, ANM, and doubly modified starch, AAR) were then tested in order to select the material with the best hydrophobic characteristics. The films were produced by the casting technique, using fixed concentrations of starch and sorbitol (4 and 1.2 g/100 g of film-forming solution, respectively). The hydrophobic characteristic of the matrices was evaluated by determining the solubility, degree of swelling, permeability to water vapor, and contact angle. In addition, emulsions were produced using the Pickering technique with different concentrations of oil and starch and then, characterized for stability, particle size, and polydispersity. The results of the extraction showed higher yields under temperatures of 80°C and better antioxidant activity at 60°C. The Peleg model presented a good fit, observing high correlation coefficients (R2> 0.90). The characterization of the films produced with different modified starches showed that AR formed matrices with higher contact angle, lower degree of swelling, and higher mechanical resistance. Emulsions with the highest degree of stability were produced with high concentrations of oil and starch (15 and 12 g/100 g of emulsion, respectively). The films produced with oil incorporation in the form of Pickering emulsion presented a more hydrophobic characteristic, and the structural characteristics were also altered with the increase of oil concentration. The films produced with the incorporation of oil in emulsion form presented total phenolic contents of 0.19 to 5.68 mg of gallic acid equivalent/100 g of films. However, the films did not present antioxidant activity against the DPPH• radical.

Des émulsions particulièrement stables peuvent être formulées à l'aide de particules colloïdales (émulsions dites de Pickering). L'objectif de cette étude est d'accéder à la compréhension des mécanismes de stabilisation des interfaces, ainsi que du lien entre propriétés interfaciales et propriétés macroscopiques des émulsions. Dans ce cadre, la stratégie adoptée repose sur l'utilisation de particules colloïdales dont les caractéristiques peuvent être variées continûment à la fois en amont par la chimie de synthèse (variation de la mouillabilité, de la déformabilité) et in situ par un stimulus (pH, sel, température...). De plus, les émulsions stabilisées par de telles particules deviennent, elles aussi, sensibles aux stimuli et la déstabilisation des émulsions peut être déclenchée à la demande. Les mécanismes d'adsorption, les interactions entre particules aux interfaces et les propriétés résultantes des émulsions sont étudiés. L'établissement de concepts généraux régissant la stabilisation/déstabilisation des émulsions permet d'en contrôler, via la formulation ou le procédé (température, cisaillement), les propriétés d'usage. Enfin les émulsions stabilisées par des particules colloïdales peuvent être utilisées en tant que précurseurs dans la formulation de matériaux plus complexes : ceci est illustré par l'élaboration de capsules à libération thermostimulée.

Monodispersed droplets were produced in a microfluidic T-junction by controlling flow rates of dispersed and continuous phases. The space between each droplet was controlled and it was similar between different droplets. The main observation of the experiments is that the droplet size is directly proportional to the flow rate of dispersed phase and inversely proportional to the flow rate of the continuous phase. The effect of viscosity on drop size is not straightforward but the influence of viscosities on droplet formation can be deduced from the capillary number. In the squeezing regime droplets are sheared off right at T-junction and the breakup is dominated by the interfacial tension force. As the velocity of the driving flow increases so called the dripping and jetting regimes happen, and the interfacial velocity is not high enough for clean snap-off, and fluids proceed in laminar flow for some distance before the snap-off occurs. Adding clay in dispersed phase slightly increases the droplet size and capillary value. Even in the same regime for different viscosities in continuous phase, capillary number varied a lot but not as much for the clay. We expect either higher concentration of clay or sufficient time needs to affect the clay on droplet size effectively.The most stable water-in-oil emulsions was formed in the experiment by using Laponite RD as emulsifier under conditions where the particles are flocculated via salt at higher concentrations of clay and high viscous polar oil (castor oil) used as continuous phase. Emulsions have been generated in a T-junction in two situations. First, emulsions at constant salt concentration for different clay concentrations. Second, emulsions at constant concentration of Laponite RD with decreasing concentration of salt. The changes in the drop size distributions with time are rationalized in terms of either coalescence or Ostwald ripening which is prompt initially but eventually stable. Emulsions were made with both non-polar oil (silicone oil) and polar oil (castor oil). It was found that the stability of emulsions dependent on the type of oil. Nonpolar oils like silicon oil was not suitable for preparing stable W/O emulsions, whereas polar oil like castor oil made stable W/O emulsions possible.

La situation durable de volatilité des prix du pétrole est considérée à la fois comme une menace et un défi par l'industrie pétrolière. Au cours de cette crise, les compagnies pétrolières ont l’opportunité de se recentrer sur la recherche de solutions de production rentables, ce qui implique souvent l’apport des nouvelles technologies, en plus de l'amélioration des processus.Ce travail présente une avancée pour la synthèse d’une nouvelle génération de fluides de forage pétrolier sans surfactants/émulsifiants pour des applications dans le forage des puits profonds et ultra profonds. Cette nouvelle génération repose sur l’introduction des émulsions de Pickering dans la formulation des fluides de forage. Ces dernières sont des émulsions stabilisées uniquement par des particules solides (dans ce cas des particules de silice). Différents types de nano particules de silice de différentes hydrophobicités ont été utilisées pour stabiliser des fluides de forage de types huile-dans-eau et eau-dans-huile. Ces fluides ont été conçus pour être utilisés dans des conditions hostiles de température et de pression. Par conséquent, une caractérisation expérimentale de leur stabilité ainsi que de leurs propriétés rhéologiques sous ces conditions extrêmes étaient nécessaires. Au cours de ce travail, les profils rhéologiques de ces fluides reflétant leurs capacités de nettoyage du puits, leur coulabilité ainsi que leurs capacités à transporter les débris jusqu'à la surface, ont été établis. D’autre part, la stabilité électrique des émulsions ainsi que leur morphologie (distribution de taille des gouttelettes) ont été étudiées et une comparaison avec celles stabilisées par des agents tensioactifs a été établie. Les fluides ont été exposés à un processus de vieillissement qui permet d’étudier l'effet de l'environnement du réservoir hostile sur la stabilité et la rhéologie des nouveaux fluides préparés. Ces fluides de haute qualité se sont révélés très fiables, offrant une grande stabilité et une capacité à résister à des conditions extrêmes de réservoir. Ils représentent une nouvelle génération de fluides de forage ouvrant la voie à une exploitation optimisée de réservoirs profonds et ultra profonds
This enduring situation of volatile oil prices has been seen as a decline and a challenge at the same time for the oil and gas industry. It is during this slump that the oil and gas companies own the opportunity to focus on cost-effective production solutions, which very often means bringing new technologies and further improving processes.This work presents a novel frontier of surfactant-free drilling and completion fluids for deep and ultra-deep wells. This new generation of drilling fluids is based on the principle of Pickering emulsions (emulsions stabilized solely by solid nano particles). Hydrophobic and hydrophilic silica nano particles were used to stabilize Oil-Based Mud and Water-Based Mud. These fluids were designed to be used under hostile conditions of temperature and pressure. Therefore, a concrete characterization of their stability as well as their rheological properties under HTHP conditions was mandatory. Rheological profiles reflecting the flowability, hole cleaning capacity as well as cutting transport ability of the fluids were established. On the other hand, the electrical stability as well as the morphology (Droplet Size Distribution) of the emulsions were studied and compared with surfactant-stabilized drilling fluids. The fluids were submitted to an aging process allowing one to study the effect of hostile reservoir environment on the stability and rheology of the new fluids prepared.These high quality fluids were seen very reliable offering high stability as well as high capacity to withstand extreme reservoir conditions giving rise to a new generation of drilling fluids allowing breaking the frontiers of deep and ultra-deep reservoirs

L’encapsulation est une technique employée couramment par le milieu industriel, notamment dans le domaine du médical, de la parfumerie ou de la cosmétique. Afin de répondre aux attentes et de proposer des capsules modulables pour tous types d’applications, des capsules de type coeur-écorce ont été élaborées au cours de cette thèse. Elles sont obtenues à partir d’émulsion dont le coeur huileux est enrobé par une coque de silice, via la minéralisation de l’interface eau-huile. Les émulsions de Pickering, stabilisées par des particules colloïdales, sont particulièrement stables et intéressantes pour cette étude. Le but de cette thèse est de comprendre, dans un premier temps, les mécanismes fondamentaux impliqués dans le processus de fabrication. Cela a permis d’élaborer, par la suite, des matériaux hybrides complexes à différentes échelles, du micrométrique au nanométrique,mais également d’établir les mécanismes de libération par un stimulus externe. Enfin, une encapsulation maîtrisée permet d’allier stabilité au stockage et destruction rapide ou contrôlée à l’utilisation. Ainsi, par diverses méthodes définies dès la formulation de l’émulsion initiale, le contenu huileux des capsules peut être libéré de manière provoquée par une action mécanique ou par l’augmentation de la température (macroscopique ou local par hyperthermie magnétique)
Encapsulation is a technique used in the industry, in particular in the field of medical,perfumery or cosmetics. In order to meet the expectations and propose adaptable capsules for all types of applications, core-shell capsules type were developed during this thesis.There were based on emulsions science with an oily core coated by a silica shell,synthetized by sol-gel chemistry at the oil-water interface. Pickering emulsions, which are emulsions stabilized by colloidal particles, are particularly stable and interesting for this study. The aim of this thesis is to understand, at first, the fundamental mechanisms involved in the manufacturing process. This made it possible to develop complex hybrid materials at different scales, from micrometric to nanometric, but also to establish the releasing mechanisms by an external stimulus. Thanks to a controlled encapsulation, it is possible to combine stability (storage) and rapid or controlled destruction when used. Thus, by various method, defined from the formulation of the initial emulsion, the releasing of the oily contentcan be caused by mechanical action or by an temperature increased (macroscopically orlocally by magnetic hyperthermia)