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GIUSTRA, MARCO DAVIDE. "Synthesis of multi-branched polymers for the stabilization of metallic nanoparticles." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/366171.
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È fondamentale progettare e monitorare tutte le fasi preparative di un sistema di drug delivery in modo tale da raggiungere un determinato sito bersaglio. Ogni parte di un nanocarrier influenza sé stesso e l'ambiente circostante. Inoltre, per ottenere campioni monodispersi, il rivestimento e le eventuali funzionalizzazioni sono fondamentali per determinare la stabilità colloidale, prevedere il comportamento in un sistema biologico e raggiungere il target di interesse. In particolar modo, la razionalizzazione dei meccanismi di internalizzazione e la quantificazione dei carrier nei siti intracellulari è ancora oggi un tema di grande interesse in ambito nanomedico.
In questo lavoro, è stata presentata una classe di polimeri multidentati di facile sintesi mostrando un'ampia applicabilità in combinazione con nanoparticelle (NPs) metalliche. I polimeri multidentati sono stati coinvolti in tre diversi progetti. Il primo progetto mirava a presentare un polimero multidentato come modello generale da applicare nel rivestimento di superfici metalliche. Per dimostrarlo sono stati effettuati diversi test prendendo in considerazione la composizione e la dimensione delle NPs. Questo polimero è stato confrontato con altri due tipi di rivestimenti comuni in letteratura. I dati ottenuti mostrano come il nuovo rivestimento fornisca una maggiore stabilità colloidale. In secondo luogo, sono stati ottenuti miglioramenti dal punto di vista della tossicità e della bio-funzionalizzazione.
Nel secondo progetto, la catena polimerica è stata modificata con un altro ligando per ampliare il campo di applicazione di questi polimeri. La scelta della molecola è basata sull'affinità per alcune superfici metalliche. In questo caso la molecola scelta è il 4-amminotiofenolo, spesso utilizzata per applicazioni SERS. Inizialmente, il polimero è stato studiato rivestendo diversi tipi di NPs metalliche (oro e argento) e sono state eseguite analisi SERS. Le dimensioni e la forma hanno giocato un ruolo chiave, in particolare con le nanoparticelle cubiche concave risultando promettenti agenti diagnostici. Nella seconda parte del progetto, le nanoparticelle cubiche d'argento sono state utilizzate come modello per la valutazione del traffico cellulare e della maturazione endosomiale. Dei test preliminari sono stati effettuati a diversi pH (per emulare le variazioni di pH nelle fasi evolutive dell'endosoma) e studi in vitro sono stati eseguiti per verificare l'uptake delle NPs nelle cellule HeLa.
Il terzo progetto mirava a utilizzare il polimero sintetizzato come precursore nella sintesi di nanoparticelle anisotropiche. La forma ottenuta inizialmente è stata quella di un petalo, ma aumentando la temperatura, i petali si sono assemblati a nanofiori con un diametro al di sopra di 100 nm. La presenza del polimero SERS-attivo rende queste nanoparticelle ottimi candidati per questa tipologia di applicazione.Designing and monitoring all the preparation steps of a drug delivery system is essential to achieve a specific target. Each part of a nanocarrier affects the batch itself and the surrounding environment. In addition, to obtain monodispersed samples, the coating and any functionalization are crucial to determine the colloidal stability, to predict the behavior with a biological system, and the reaching of the target site. In particular, the achievement of intracellular sites by rationalizing the internalization mechanisms and quantifying the carriers in the target is still today a hot topic in the nanomedical field. Here, a class of multidentate polymers was presented: a simple way to synthesize them and show their broad applicability in combination with metal NPs. Multi-branched polymers were involved in three projects. The first project aimed to present a multidentate polymer as a general model to be applied in the coating of metal surfaces. To prove this, several tests were carried out by modulating the composition and size of the NPs. This easily synthesized polymer has been compared with two types of coatings common in literature. The obtained data show how the new surfactant provides high colloidal stable nanoparticles. Secondly, this leads to improvements from the point of view of toxicity and bio-functionalization. In the second project, the ligands polymer chain was modified to increase the range of application. Moreover, the choice of the ligand was based on the affinity for certain metal surfaces. In this case, the molecule is 4-aminotiophenol which is often used for SERS applications. Initially, the versatility of the polymer was investigated by coating different types of metallic NPs (gold and silver) and then SERS analyses were performed. Size and shape played a key role, especially with cubic concave nanoparticles that are promising for diagnostics application. In the second part of the project, cubic silver nanoparticles were used as a model for the evaluation of cell trafficking and endosomal maturation. Preliminary tests of NPs have been carried out at different pH (to emulate the pH variations in the endosomal evolution stages) and in vitro studies to check the nanoparticles uptake in HeLa cells were performed. The third project aimed to use the designed polymer as precursor in the synthesis of anisotropic nanoparticles. The shape obtained is a petal form. Subsequently, with the increase of the temperature, the petals assembled to nanoflowers above 100 nm. The presence of the active SERS polymer makes these nanoparticles, excellent candidates for this application.
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Jones, David Andrew Ross. "Depletion flocculation of sterically-stabilized particles." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364692.
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Ryan, Joseph Nolte. "Groundwater colloids in two Atlantic coastal plain aquifers : colloid formation and stability." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14560.
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Norrfors, Karin. "Stability and sorption capacity of montmorillonite colloids : Investigation of size fractional differences and effects of γ-irradiation." Doctoral thesis, KTH, Tillämpad fysikalisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-159944.
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Bentonite clay is intended to form one of the barriers in most repositories of spent nuclear fuel located in granite. One important function of the bentonite barrier is to retard transport of radionuclides in the event of waste canister failure. Bentonite has a high sorption capacity of cations and its main constituent is montmorillonite. In contact with groundwater of low ionic strength, montmorillonite colloids can be released from bentonite and thereby control transport of radionuclides sorbed onto the colloids. In colloid transport in bedrock fractures, size separation of clay colloids may occur due to physical and chemical interactions with the bedrock fracture surface. This may enhance or retard the overall transport of radionuclides, depending on the sorption capacities and stability of the differently sized clay colloids. The bentonite barrier will be exposed to γ-radiation from the spent nuclear fuel. Irradiation affects surface-related properties of bentonite. If an average sorption capacity value cannot be used for all colloid sizes or if sorption is affected by exposure to γ-irradiation, corrected sorption capacity values would give higher resolution in current reactive transport models. In order to study the size separation process, a protocol was developed and successfully applied to fractionate montmorillonite into different-sized colloid suspensions by means of sequential or direct centrifugation. The stability and sorption capacity were studied using these fractions. Both stability and sorption capacity were found to be similar for all colloid sizes. Bentonite exposed to γ-radiation sorbed less divalent cations with increasing radiation dose. The effect was not large enough to have any impact on diffusion. The presence of bentonite enhanced irradiation-induced corrosion of copper under anaerobic atmosphere. An average sorption capacity value for montmorillonite can be used for all colloid sizes in reactive transport models. The effect of γ-irradiation on sorption capacity is sufficiently large to require consideration in transport modelling.Bentonite är planerad som en av barriärerna i de flesta slutförvar av använt kärnbränsle. Bentonite har en hög sorptionskapacitet för katjoner. Den huvudsakliga beståndsdelen av bentonit är montmorillonit. Montmorillonitkolloider kommer att frigöras från bentonitbufferten i kontakt med grundvatten av låg jonstyrka och på så vis styra transporten av sorberade radionuklider. Under den kolloidala transporten i bergsprickorna kan en separation med avseende på storlek uppstå genom interaktioner mellan kolloiderna och bergytan. Detta kan få till följd att den genomsnittliga transporten av radionuklider bromsas eller tilltar beroende på sorptionskapaciteten och stabiliteten av de olika kolloidstorlekarna. Bentonitbarriären kommer även att utsättas för γ-bestrålning från det använda kärnbränslet, vilket påverkar dess ytrelaterade egenskaper. Om inte ett medeltal för sorptionskapaciteten är giltigt för alla kolloidstorlekar eller om sorptionen påverkas av γ-bestrålning, behövs nya sorptionskapaciteter bestämmas och impliceras för noggrannare transportmodeller. En metod för att separera montmorillonitkolloider med avseende på storlek via direkt och stegvis centrifugering har utvecklats. Stabiliteten och sorptionskapaciteten för dessa fraktioner har studerats. Både stabilitet och sorptionskapacitet visade sig vara lika för alla kolloidstorlekar. Bestrålad bentonit sorberar mindre andel divalenta katjoner med ökad dos bestrålning. Effekten är dock inte stor nog för att slå igenom i diffusionsexperimenten. Förekomst av bentonit ökar även den strålningsinducerade korrosionen av koppar under anaeroba förhållanden. Ett medelvärde för sorptionskapaciteten kan användas för alla kolloidstorlekar i transportmodeller. Effekten av γ-bestrålning är dock stor nog för att implementeras i modellerna.
QC 20150213
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COLANGELO, DONATO. "Nuovi approcci alla chiarifica dei mosti e al fining dei vini per la stabilità colloidale." Doctoral thesis, Università Cattolica del Sacro Cuore, 2019. http://hdl.handle.net/10280/57884.
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Per via degli svantaggi inerenti l’uso di bentonite nella produzione di vini bianchi, la ricerca di alternative ha assunto di recente una grande importanza. Il lavoro presentato in questa tesi ha l’obiettivo di valutare l’applicabilità di tre approcci innovativi alla stabilizzazione colloidale dei vini: l’uso di chitosano, l’applicazione dei PEF e il riutilizzo di colonne di scambio cationico.
L’aggiunta di chitosano è risultata nella rimozione delle chitinasi dal vino, permettendo di raggiungere un soddisfacente livello di stabilità. Gli effetti sul colore e sugli aromi, quando non significativi, non sono risultati essere peggiori rispetto ai risultati ottenuti da trattamenti con bentonite.
L’applicazione dei PEF aveva lo scopo di innescare la denaturazione e l’aggregazione delle proteine tramite un sistema di trattamento-raffreddamento e filtrazione finale. I risultati suggeriscono che un buon grado di stabilità viene raggiunto solo con trattamenti particolarmente energetici ma questo a danno del colore del prodotto.
Infine, lo scopo dello studio sulle resine di scambio cationico era quello di valutare la rigenerazione di questo supporto per un molteplice utilizzo operativo. La rimozione delle proteine adsorbite sul supporto è risultata essere possibile in specifiche condizioni di pH e forza ionica, con un consumo di acqua relativamente basso.The search for fining alternatives to bentonite has assumed great importance in white winemaking due to the drawbacks of bentonite application. The research here presented aimed at observing the viability of three innovative approaches to wine stabilization, namely chitosan addition, PEF treatments and cation exchange applicability. Chitosan successfully removed chitinases from wine, allowing at the same time a sufficient degree of colloidal stability. Collateral effects on color and aroma compounds were non-significant or acceptable when compared with the effects observed for bentonite applications reported in literature. The use of PEF was aimed at accelerating protein unfolding and aggregation and was coupled to an in-line cooling and filtration system for efficient removal of colloidal aggregates. The results collected suggested that the treatment was capable of inducing a satisfactory colloidal stability only in high- energetic double-treated wine samples, with some deleterious consequences on the color. Finally, the aim of the research for cation-exchange resins application was to find environmentally friendly cleaning procedures to regenerate the resin capacity and allow reuse of the same resin for further cycles of fining. The removal of proteins bound to the resin was possible under specific pH and ionic strength conditions with relatively low consumption of water.
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Zhang, Li. "The study of phase separation in the miscibility gap and ion specific effects on the aggregation of soft matter system." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS106/document.
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Le procédé de séparation de phase est importante car elle détermine la structure des matériaux finaux. Il existe de nombreux systèmes qui ont plus d'une phase tels que des mousses et des gels. Les mousses sont des dispersions aqueuses de bulles de gaz dans une phase aqueuse et gels apparaissent lorsque certains microscopique unité de base commence à se rassembler formant un grand réseau solide qui enjambe l'espace macroscopique. Ils ont de nombreuses applications dans l'industrie et la vie quotidienne. Dans cette thèse, tout d'abord, je me concentre sur l'étude de différents types de séparation de phase. Deuxièmement, je étudié les effets spécifiques d'ions sur l'agrégation des particules colloïdales et tensioactif, le but est de faire des mousses stables. Dans la lacune de miscibilité il existe deux types de séparation de phase: la croissance nucléation et la décomposition spinodale, ils ont différents mécanismes et de la cinétique de croissance. Par conséquent, mon premier projet est d'étudier le processus d'évolution d'eux et de leurs effets sur la structure finale du matériau. Les gels peuvent être préparés par l'ajout de sel à la dispersion de particules colloïdales, ils ont un grand nombre d'applications telles que dans les aliments et la science des matériaux. Dans cette thèse, nous utilisons différents types de sels de comparer les propriétés de gel à partir de deux aspects macroscopiques et microscopiques. Obtenir des mousses stables est significatif dans la vue de leur beaucoup d'applications, mais les moyens de les faire sont pour la plupart compliqué. Dans cette thèse, nous pouvons obtenir des mousses stables par l'intermédiaire de deux façons. On est tout simplement en ajoutant des sels de solutions de tensioactifs, à travers lequel nous pouvons faire la mousse ultra-stable. Une autre façon est d'utiliser la phase de gel, nous avons étudié en tant que phase continue dans les mousses à arrêter le vieillissement de la moussePhase separation process is important as it determines the structure of the final materials. There are many systems that have more than one phase such as foams and gels. Aqueous foams are dispersions of gas bubbles in a water phase and gels appear when some basic microscopic unit starts to aggregate forming a large solid network that spans macroscopic space. They have many applications in industry and daily life. In the present thesis, firstly, I focus on studying different types of phase separation. Secondly, I studied the ion specific effects on the aggregation of colloidal particles and surfactant, the purpose is to make stable foams. In the miscibility gap there are two types of phase separation: Nucleation growth and spinodal decomposition, they have different growth mechanisms and kinetics. Therefore, my first p project is to investigate the evolution process of them and their effects to the final structure of material. Gels can be made by adding salt to the dispersion of colloidal particles, they have a large number of applications such as in food and material science. In this dissertation, we use different types of salts to compare gel properties from both macroscopic and microscopic aspects. Obtaining stable foams is significant in the view of their plenty of applications, but the ways to make them are mostly complicated. In this thesis, we can obtain stable foams via two ways. One is simply by adding salts to surfactant solutions, through which we can make ultrastable foam. Another way is using the gel phase we have studied as the continuous phase in foams to arrest the foam aging
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Dale, Phillip. "The colloidal stability of suspo-emulsions." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398542.
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Whyman, R. H. "Electrophoretic and stability studies of casein coated colloidal particles." Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379647.
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Czigány, Szabolcs. "Subsurface colloids stability, sampling, and transport under gravitational and centrifugal accelerations /." Online access for everyone, 2004. http://www.dissertations.wsu.edu/Dissertations/Summer2004/s%5Fczigany%5F080404.pdf.
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Herman, David J. "Controlling Colloidal Stability using Highly Charged Nanoparticles." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51566.
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This dissertation focused on the potential use of highly charged nanoparticles to stabilize dispersions of weakly charged microparticles. The experimental components of the project centered on a model colloidal system containing silica microparticles at the isoelectric point where the suspensions are unstable and prone to flocculation. The stability of the silica suspensions was studied in the presence of highly charged nanoparticles. Initial experiments used polystyrene latex with either sulfate or amidine surface groups. Effective zeta potentials were measured with nanoparticle concentrations ranging from 0.001% to 0.5% vol. Adsorption levels were determined through direct SEM imaging of the silica microparticles, showing that the nanoparticles directly adsorbed to the microparticles (amidine more than sulfate), producing relatively large effective zeta potentials. However, stability experiments showed that the latex nanoparticles did not stabilize the silica but merely provided a reduction in overall flocculation rate. It was concluded that the zeta potential was an insufficient predictor of stability as there was still sufficient patchiness on the surface to allow for the silica surfaces to aggregate.
Experiments using zirconia and alumina nanoparticles did achieve effective stabilization; both types stabilized the silica suspensions for longer than the observation period of approximately 15 hours. Stability was observed at concentrations of 10^-4% to 1.0% (zirconia) and 10^-2% vol. (alumina). These particles adsorbed directly to the microparticles (confirmed via SEM) and produced increasing effective zeta potentials with increasing nanoparticle concentrations. The adsorption resulted in significant electrostatic repulsion that was determined to be effectively irreversible using colloidal probe AFM. The improved stabilizing ability was attributed to the increased van der Waals attraction between the oxide nanoparticles (compared to polystyrene).
Finally, an unexpected result of the CP-AFM force measurements showed that the repulsive forces between a nanoparticle-coated particle and plate lacked the normal dependence on the radius of the probe as predicted by the Derjaguin approximation. The forces observed in nanoparticle suspensions were virtually identical for 5 µm and 30 µm probes. Based on calculations of the shear rate in the gap, it was theorized that this phenomenon may have resulted from the shearing of adsorbed particles from the surfaces, which leads to similar interaction geometries for the two probe sizes.Ph. D.
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Garcia, Garcia Sandra. "Generation, stability and migration of montmorillonite colloids in aqueous systems." Stockholm : Skolan för kemivetenskap, Kungliga Tekniska högskolan, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11847.
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Jia, Zichen. "Stability, aggregation kinetics and aggregates thermal restructuring of polymer colloids /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16913.
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García, García Sandra. "Generation, stability and migration of montmorillonite colloids in aqueous systems." Doctoral thesis, KTH, Kemiteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11847.
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In Sweden the encapsulated nuclear waste will be surrounded by compacted bentonite in the granitic host rock. In contact with water-bearing fractures the bentonite barrier may release montmorillonite colloids that may be further transported in groundwater. If large amounts of material are eroded from the barrier, the buffer functionality can be compromised. Furthermore, in the scenario of a leaking canister, strongly sorbing radionuclides, can be transported by montmorillonite colloids towards the biosphere. This thesis addresses the effects of groundwater chemistry on the generation, stability, sorption and transport of montmorillonite colloids in water bearing rock fractures. To be able to predict quantities of montmorillonite colloids released from the bentonite barrier in contact with groundwater of varying salinity, generation and sedimentation test were performed. The aim is first to gain understanding on the processes involved in colloid generation from the bentonite barrier. Secondly it is to test if concentration gradients of montmorillonite colloids outside the barrier determined by simple sedimentation experiments are comparable to generation tests. Identical final concentrations and colloid size distributions were achieved in both types of tests. Colloid stability is strongly correlated to the groundwater chemistry. The impact of pH, ionic strength and temperature was studied. Aggregation kinetics experiments revealed that for colloid aggregation rate increased with increasing ionic strength. The aggregation rate decreased with increasing pH. The temperature effect on montmorillonite colloid stability is pH-dependent. At pH≤4, the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH≥10, the aggregation rate constant decreased with increasing temperature. In the intermediate pH interval, the aggregation rate constant decreased with increasing temperature except at the highest ionic strength, where it increased. The relationship between the rate constant and the ionic strength allowed the critical coagulation concentration (CCC) for Na- and Ca-montmorillonite to be determined. In order to distinguish the contribution of physical filtration and sorption to colloid retention in transport, the different retention mechanisms were quantified. Sorption on different representative minerals in granite fractures was measured for latex colloids (50, 100, 200 nm) and montmorillonite colloids as a function of ionic strength and pH. Despite of the negative charge in mineral surfaces and colloids, sorption was detected. The sorption is correlated to the mineral point of zero charge and the zeta potential of the colloids, and increases with increasing ionic strength and decreasing pH. In transport experiments with latex colloids in columns packed with fracture filling material, the retention by sorption could clearly be seen. In particular at low flow rates, when the contact time for colloids with the mineral surfaces were the longest, sorption contributed to retention of the transport significantly. The retention of latex colloids appeared to be irreversible in contrary to the reversible montmorillonite colloid retention. Generation, stability and sorption of the montmorillonite colloids are controlled by electrostatic forces; hence, the results were in qualitative agreement with DLVO.
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Collins, Ian R. "The colloid stability of gold particles dispersed on solid surfaces." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292530.
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Alhummiany, Haya A. "The structure and stability of colloidal nanoparticle assemblies." Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604308.
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Thiol-passivated gold nanoparticies deposited onto a silicon substrate from an organic solvent form a remarkable variety of self-organised nanostructured and microstructured patterns. The work in this thesis focuses on three key aspects of these systems: (i) their environmental stability, (ii) the formation of nanoparticie rings via condensation of water droplets, and (iii) the morphology of nanoparticie mono layers formed at the water-air interface and transferred to silicon substrates using the Langmuir-Blodgett technique. The nanoparticie structures were studied by combined atomic force microscopy (A FM) and contrast-enhanced optical microscopy. Striking changes in the morphology of self-organised nanoparticie patterns are observed during exposure to high humidity or high temperature environment. Annealing the sample at 1200 C leads to a high degree of nanoparticie sintering promoted by break-up of the initial assembly. Conversely, exposing the sample to a high relative humidity (80%) environment induces layer-by-layer assembly of 3D aggregates with no evidence of sintering. We focus also on the formation of rings of thiol-passivated Au nanoparticies, addressing the controversy in the literature regarding the formation of these structures. We provide compelling evidence that nanoparticie rings formed via the adsorption of droplets of condensed water. This so-called "breath figure" effect plays the dominant role in the dynamics of ring formation via iii evaporative dewetting. Different sizes and size distributions of nanoparticle rings have been created under controlled relative humidity environments ranging from ~50% to 80%. Fmthermore, the dynamic behaviour of water droplets on surface has been examined using a contrast-enhanced optical mIcroscope. Analysis of the observed droplet dynamics shows significant differences between the behaviour of droplets formed on top of a silicon substrate and the nanoparticle films. Finally, the formation of gold nanoparticle assemblies at the water-air interface using the Langmuir-Blodgett deposition technique has also been studied. The LB films were transferred to a solid substrate (silicon) and the nanoparticle assemblies fOlmed close to the contact line imaged by AFM and contrastenhanced optical microscopy. The experimental control parameters resulted in the emergence of variety of nanoparticie morphologies. We propose formation mechanisms for a number of these morphologies.
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Somani, Vaibhav (Vaibhav Basantkumar). "Colloidal stability of magnetic nanoparticles in molten salts." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59250.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Includes bibliographical references.
Molten salts are important heat transfer fluids used in nuclear, solar and other high temperature engineering systems. Dispersing nanoparticles in molten salts can enhance the heat transfer capabilities of the fluid. High temperature and high ionicity of the medium make it difficult to make a colloidally stable dispersion of nanoparticles in molten salts. The aggregation and sedimentation kinetics of different nanoparticles dispersed in molten salts is studied, and trends of settling rates with system parameters like particle size, temperature and concentration are observed. Finally, a hypothesis based on ultra low values of Hamaker coefficient is suggested in order to achieve long term colloidal stability in molten salts medium.
by Vaibhav Somani.
S.M.
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Alousque, Fanny. "Etude de la stabilité colloïdale du latex de caoutchouc naturel." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066648.
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Cette thèse, menée en collaboration avec Michelin dans le cadre de la fabrication de matériaux composites, porte sur la stabilité colloïdale du latex de caoutchouc naturel (NR). Ce latex est une dispersion colloïdale polydisperse d'un polymère naturel dans un sérum aqueux. Les particules sont stabilisées par une couche complexe de phospholipides et de protéines. Cette dispersion peut être coagulée de façon irréversible par voie physique (sous cisaillement) ou par voie physico-chimique (ajout de cations divalents ou de particules hydrophobes). Dans ce travail, nous avons étudié la coagulation du latex par les cations divalents. Pour cela nous avons utilisé des outils physico-chimiques : diagrammes de stabilité en présence de divers cations, suivi cinétique de l'agrégation des particules et mesures rhéologiques. Ensuite, nous avons sondé la surface de particules de NR, par électrophorèse, en présence de tensioactifs et aussi selon la taille des particules. Pour expliquer la coagulation, nous suggérons que l'augmentation de la force ionique écrante les interactions répulsives et que les cations forment des ponts ioniques entre les particules. Ces ponts les maintiennent au contact et l'irréversibilité du phénomène est assurée par l'adhésion entre les chaines de polymères proches de la surface. L'adsorption des tensioactifs modifie la surface des particules et la coagulation du latex. Une légère différence de charge de surface a été observée entre les particules de NR selon leur taille. Enfin, un phénomène de coagulation similaire a été obtenu avec un latex synthétique, ce qui ouvre la voie à l'exploitation industrielle de ce phénomène de coagulationThis work, in collaboration with Michelin for the fabrication of composite materials, deals with the colloidal stability of the latex of natural rubber (NR). The NR latex is a polydisperse colloidal dispersion of a bio-polymer in an aqueous serum. The particles are stabilized by a complex layer of phospholipids and proteins. This dispersion can be coagulated by a physical way (under shearing), or by a physical-chemical way (addition of divalent cations or hydrophobic particles). In this thesis, we studied the coagulation of the NR latex by divalent cations with physical-chemical tools (stability diagrams with different cations, aggregation kinetic of particles, rheological measuremments). Then, the surface of NR particles has been characterized by electrophoresis, firstly in the presence surfactants and secondly depending on the particles size. From the results of the first part we suggest that the coagulation with divalent cations is due to a screening effect because of the increase of ionic strength and that divalent cations can bridge the particles together. This allows keeping them in contact. Adhesion between polymer chains near the surface ensures the irrversible cohesion. In a second time, we saw that the adsorption of surfactants changes the particles surface and the coagulation of NR latex with cations. A small difference of surface charge is observed between the biggest and the smallest NR particles. Finally, a similar behavior has been obtained with a synthetic latex in presence of divalent cations. Our results could be used to develop an industrial process based on this coagulation phenomenon
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Bsaibess, Talia. "Nanoparticules organiques ultra-brillantes pour l'imagerie biologique." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0055/document.
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Les nanoparticules inorganiques luminescentes ont suscité un intérêt croissant au cours des dernières décennies, notamment pour leur application en imagerie biologique. Un certain nombre d’entre elles présentent toutefois des limitations telles que toxicité, absence de biodégradabilité, faible brillance, clignotements…. Dans cette optique, les nanoparticules fluorescentes à base de petites molécules organiques (FONs) offrent une solution alternative prometteuse aux nanoparticules inorganiques pour l'imagerie biologique. Le principal défi réside dans l'élaboration des nanoparticules organiques possédant une brillance élevée, une bonne stabilité dans l'eau (y compris en milieu biologique), une bonne biocompatibilité ainsi qu'une émission accordable dans le visible et au-delà dans le proche infrarouge (pour une détection plus aisée en milieu diffusant). Dans cette optique, nous avons utilisé une stratégie basée sur l’utilisation de chromophores dipolaires de type "push pull" « adaptés ». Au cours du travail, la synthèse de séries de chromophores homologues bâtis sur le même système conjugué et ayant en commun un groupe donneur de type triphénylamine (destiné à préserver les propriétés de luminescence) présentant ou non des motifs encombrants positionnés a été réalisée. Les nanoparticules correspondantes ont été préparées selon un protocole classique, simple et rapide à mettre en oeuvre (précipitation). L’étude des propriétés photophysiques des nanoparticules organiques fluorescentes ainsi obtenues a été réalisée et mise en perspective avec celles des chromophores en solution dans des solvants organiques de polarité variable. Une étude systématique de l’évolution dans le temps des propriétés optiques des nanoparticules organiques a été réalisée permettant de mettre en lumière des relations entre la structure des sous-unités chromophoriques et la stabilité colloïdale et « optique » des nanoparticules. Ces études ont permis d’identifier des nanoparticules émettant dans le proche infrarouge extrêmement brillantes et présentant une stabilité colloïdale remarquable dans l’eau, une photostabilité accrue et une très bonne biocompatibilité. De ce fait, ces nanoparticules ont pu être utilisées avec succès dans l'imagerie biologique des cellules et le suivi (tracking) à l'échelle de la particule unique, démontrant l'intérêt de la démarche d'ingénierie mise en oeuvreDuring the last decades, luminescent inorganic nanoparticles have attracted a large interest in different fields including biological imaging. However, a number of them have drawbacks such as toxicity and absence of biodegradability. Recently, molecular-based fluorescent organic nanoparticles (FONs) have emerged as a promising alternative to inorganic nanoparticles for bioimaging. The main challenge lies in the elaboration of organic nanoparticles that combine large brightness, good colloidal stability in biological environments) and biocompatibility as well as NIR emission (to allow improved detection in thick tissues). To achieve this objective, we have implemented a molecular engineering strategy based on dedicated polar and polarizable "push pull" chromophore built from a triphenylamine donor moiety and a specific pi-conjugated system. The corresponding nanoparticles were readily prepared by the reprecipitation method. In the present manuscript, the synthesis of the chromophores and the preparation and characterization of the organic fluorescent nanoparticles is described. A comprehensive investigation of their photophysical properties and study of their colloidal stability is presented allowing to derive structure-property relationships. The implemented study led to innovative NIR-emitting nanoparticles combining large brightness (superior to those of QDs and NIR-emitting organic dyes), remarkable colloid stability and suitable photostability. These nanoparticles have been successfully used for single particle tracking and imaging in cells, while no toxic effect was observed
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Wang, Gonghou. "Ionic stability of oxide particles in polar organic media /." *McMaster only, 1998.
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Vautrin, Claire. "Stabilité et struture d'agrégats catanioniques." Versailles-St Quentin en Yvelines, 2004. http://www.theses.fr/2004VERS0003.
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Le système catanionique CTAOH - C13COOH - H2O étudié forme des colloi͏̈des de charge contrôlée lorsque les tensioactifs sont mis en solution. Le diagramme de phase établi ici présente des agrégats particuliers (micelle, vésicule, disque, phase lamellaire). L'étude de la CMC a fait apparaître des interactions fortes entre monomères : le coefficient d'interaction est de -10kT. Du point de vue microscopique, nous avons montré par diffusion couplée WAXS et WANS que les chaînes alkyl s'organisent suivant un réseau hexagonal et que les têtes ioniques conservent un ordre liquide. Par ailleurs, les liaisons hydrogène participent à la cohésion du système, et les propriétés mécaniques de la membrane sont assez proches de celles d'un phospholipide. Les mesures des compressibilités par propagation acoustique et cuve de Langmuir nous ont permis d'estimer le module d'Young à 100MPa. L'analyse calorimétrique par DSC a montré que la transition de fusion de chaînes dépend de la composition de l'échantillonThe catanionic system hydroxide de cetyltrimetylammonium - myristic acid - water studied here has the advantage to produce aggregates with controlled charge. So, the ternary phase diagram presents some interesting aggregates (micelle, vesicle, disc, lamellar phase). The study of the CMC put in evidence some strong interactions between monomers : the interaction parameter is equal to -10kT. On a microscopic point of view, the alkyl chains packing is hexagonal and we proved by WAXS and WANS that the head groups are liquid ordered. More over, the hydrogen bonds participate to the bilayer cohesion. The mechanical properties of the catanionic membrane are similar to the properties of phospholipids. We estimated the Young modulus to 100MPa by compressibility measurements (acoustic propagation and Langmuir trough). The thermodynamic properties studied by DSC showed that the chain melting transition depends on the sample composition
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Garcia, Garcia Sandra. "The impact of groundwater chemistry on the stability of bentonite colloids." Licentiate thesis, KTH, Chemistry, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4504.
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I det svenska djupförvaret för kärnbränsle ska kompakterad bentonit användas som barriär mellan kopparkapslar med utbränt kärnbränsle och berget. I kontakt med vattenförande sprickor kan bentonitbarriären under vissa omständigheter avge montmorillonitkolloider. Förutom att barriärens egenskaper urholkas pga förlusten av material kan kolloiderna, om de är stabila, underlätta transporten av sorberade radionuklider ut mot biosfären.
Den här studien fokuserar på att undersöka vilka effekter grundvattenkemin har på montmorillonitkolloiders stabilitet. Grundvattnets sammansättning, pH och jonstyrka, kommer sannolikt att förändras under djupförvarets livslängd, delvis pga inträngandet av glactialt smältvatten. Initialt kommer omgivande berg att värmas upp pga värmealstring från det radioaktiva sönderfallet i det utbrända kärnbränslet. Effekterna av pH, jonstyrka och temperatur på montmorillonitkolloiders stabilitet har analyserats genom att följa hur kolloiderna aggregerar med tiden. Minskningen av partikelkoncentration med tiden mättes med Photon Correlation Spectroscopy (PCS).
Aggregationsexperimenten visar att, vid ett givet pH och en given temperatur, ökar hastighetskonstanten för aggregation med ökande jonstyrka. Kritiska koaguleringskoncentrationen (CCC) för NaCl och CaCl2 för Na-montmorillonit och Ca-montmorillonit beräknas utifrån ett samband mellan hastighetskonstanterna och jonstyrkan.
Hastighetskonstanten för aggregation minskar med ökande pH eftersom ytpotentialen ökar. Effekten blir tydligare vid högre jonstyrkor och högre temperaturer, men kan däremot inte observeras vid låga temperaturer.
Temperatureffekten på bentonitkolloidernas stabilitet är pH-beroende. Vid pH≤4 ökar hastighetskonstanten för kolloidaggregation med ökande temperatur, oavsett jonstyrka.Vid pH≥10 minskar hastighetskonstanten med ökande temperatur. I mellanliggande pH-område minskar hastighetskonstanten för aggregation med ökande temperatur, förutom vid den högsta jonstyrkan, där den ökade. Beräkningar baserade på DLVO-teori matchar de experimentella resultaten.
In deep geological repositories in Sweden, encapsulated nuclear waste will be surrounded by compacted bentonite in the host rock. In future contact with water-bearing fractures, this bentonite barrier can release montmorillonite colloids under certain conditions. This process can lead to loss of buffer material. Furthermore, these colloids, if stable, may facilitate the transport of associated radionuclides towards the biosphere. Colloid stability is determined by groundwater chemistry.
This study addresses the effects of groundwater chemistry on the stability of montmorillonite colloids. During the lifetime of the repository, the pH and ionic strength of the groundwater are expected to vary, partly due to intrusion of glacial melt water. Initially, the temperature will be higher in the surrounding host rock due to heat released from radioactive decay in the spent nuclear fuel. The effects of these parameters on the stability of montmorillonite suspensions were evaluated by studying the aggregation kinetics. The change in particle concentration with time was monitored by Photon Correlation Spectroscopy (PCS).
Aggregation kinetics experiments showed that for a given pH and temperature, the rate constant for colloid aggregation increased with increasing ionic strength. The relationship between the rate constant and the ionic strength allowed the NaCl and CaCl2 critical coagulation concentration (CCC) for Na- and Ca-montmorillonite to be determined.
The aggregation rate constant decreased with increasing pH as the surface potential increased. This effect became more pronounced at higher ionic strengths and higher temperatures but could not be observed at low temperature.
The effect of temperature on the stability of the suspensions is pH-dependent. At pH≤4, the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH≥10, the aggregation rate constant decreased with increasing temperature. In the intermediate pH interval, the aggregation rate constant decreased with increasing temperature except at the highest ionic strength, where it increased.
The experimental results were in agreement with DLVO calculations.
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García, García Sandra. "The impact of groundwater chemistry on the stability of bentonite colloids /." Stockholm : Kemi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4504.
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Saucier, Cédric. "Les tanins du vin : étude de leur stabilité colloi͏̈dale." Bordeaux 2, 1997. http://www.theses.fr/1997BOR20537.
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Les tanins sont des composés extrêmement importants pour la stabilité colloïdale du vin. Cette stabilité est essentielle pour la limpidité, la couleur et la saveur des vins. L'objectif de ce travail a été de déterminer la structure des tanins sous forme colloïdale en solution, et d'étudier leurs interactions avec les protéines et les polysaccharides. Des systèmes modèles contenant des formes monomères et polymères de flavanols en solution synthétiques ont été étudiés par diffusion de la lumière. On montre que ces composés peuvent s'associer sous forme colloïdale à partir d'une concentration dépendant fortement du degré de polymérisation. L'addition de protéines à ces solutions déstabilise uniquement les tanins sous forme colloïdale. Par contre, certains polysaccharides peuvent les stabiliser en s'adsorbant sur leur surface. La polymérisation de la catéchine et de l'éthanal est étudiée comme un modèle d'évolution des tanins du vin lors du vieillissement. La cinétique de la réaction et les structures des dimères formés sont étudiées par des techniques de chromatographie liquide (HPTLC, HPLC) et des techniques d'analyse structurale (RMN,ES-MS). Tout comme les tanins du vin jeune, ces molécules sont capables de s'auto-associer sous forme colloïdale et d'interagir de manière analogue avec les macromolécules. Enfin, des expériences sont conduites directement sur des vins rouges où l'on a mis en évidence la présence des dimères précédemment étudiés. Leur impact sur la couleur du vin est estimé. Les premiers résultats concernant la mise au point d'un test de stabilité colloïdale du vin rouge sont rapportés et mettent en évidence le rôle protecteur de certains polysaccharides.
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O'Keefe, Samantha Jane. "A study of the rheological properties of polymer modified cement pastes." Thesis, University of the West of England, Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293326.
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The work outlined in this thesis describes how rheological techniques can be used to gain insight into the behaviour of complex hydrating systems. These techniques are currently used to elucidate interparticle interactions of concentrated colloidal dispersions. Those used here were stress relaxation, pulse shearometry and oscillation. These enabled parameters such as the dynamic moduli, relaxation moduli, relaxation spectrum and limiting moduli to be obtained. These all give a measure of the strength of interaction of the colloidal system under different conditions, without reducing these interactions by inducing flow. Calorimetric data was obtained for a hydrating cement paste. The particle and floc size of this cement was also measured. The data were found to be in accord with one another, and with current theories of the hydration processes of cement. In combination with the rheological parameters measured this enabled the extent and strength of attraction between the particles of a cement paste to be determined, as a function of the age of the paste. The adsorption characteristics of surfactant on cement were measured, as was the effect of surfactant on the particle and floc size of hydrating cement. Coupled with a measure of the rheological parameters of the cement-surfactant system, an understanding of the effect of surfactant on a hydrating cement paste was obtained. Similarly the effect of the addition of styrene-butadiene polymer latex particles, with and without excess added surfactant, was able to be determined. This information was obtained for hydrating cement pastes, both in the presence and absence of added polymer, at both ambient and non-ambient temperatures.
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Roth, Stéphane. "Etude de films protéiques aux interfaces huile/eau par tensiométrie et rhéologie interfaciale." Dijon, 2001. http://www.theses.fr/2001DIJOS040.
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Les colloi͏̈des sont présents dans un grand nombre d'industries telles que les industries alimentaires, pétrolières, pharmaceuticales ou cosmétiques. La compréhension et la maîtrise des mécanismes de stabilisation, dépendant des propriétés interfaciales de ces systèmes, sont d'une importance primordiale, tant au niveau de la formulation que des procédés de fabrication. Dans ce travail de thèse, nous avons étudié le comportement de films protéiques (caséine ß, caséine as, caséinate, ou ß-lactoglobuline) aux interfaces huile/eau par tensiométrie, rhéologie interfaciale dilatationnelle et rhéologie interfaciale de cisaillement. Cette étude a permis de montrer l'influence des paramètres de milieu dont la présence de tensioactifs de faible masse moléculaire (monolaurine, monopalmitine, monooléine et Tween 20), du pH, de la concentration des protéines dans la phase aqueuse, la nature de l'huile et de la température. Nos résultats mettent en évidence des changements de propriétés des films protéiques interfaciaux au cours du temps, expliqués en termes de synergie, de compétitions liées à des interactions physico-chimiques ainsi qu'en terme de structurations liées à l'établissement de liaisons chimiques (polycondensation de la ß-lactoglobuline en particulier) induites ou non par chauffage. De nombreuses hypothèses ou conclusions ont été émises quant aux interactions entre surfactants à l'interface ou encore quant à l'interprétation des notions de viscosité ou élasticité de surface. La rhéologie interfaciale s'est montrée être un outil de viscosité ou élasticité de surface. La rhéologie interfaciale s'est montrée être un outil puissant pour l'étude des phénomènes de compétition, de synergie ou de déplacement et pour l'étude de la topologie des protéines adsorbées.
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Saintyves, Baudoin. "Digitation élastique en volume dans les solides mous et les matériaux viscoélastiques." Paris 6, 2013. http://www.theses.fr/2013PA066164.
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Nous avons mis en évidence l'existence d'une instabilité de digitation en volume, d'origine purement élastique, dans des gels de polyacrylamide confinés en cellule de Hele-Shaw. Cette instabilité partage certaines similarités avec la célèbre instabilité de Saffman-Taylor : l'adhésion totale de l'élastomère a pour conséquence une condition de non glissement cruciale pour la digitation. Bien qu'essentielle, cette adhésion n'intervient pas dans le bilan énergétique, ce qui est prouvé par le fait que le seuil de l'instabilité ne dépend pas du module de cisaillement. Une étude systématique a également montré que la tension de surface n'intervenait pas non plus dans le mécanisme de déstabilisation. Cette instabilité est sous-critique, avec un net comportement hystérétique. Nos observations expérimentales ont pu être comparées aux résultats d'une analyse théorique et de simulations par éléments finis, et ont montré un très bon accord. En particulier, la longueur d'onde et le seuil en avancement du front sont proportionnels à la distance qui sépare les plaques de verre constituant la cellule. Nous avons d'autre part mis en évidence le passage continu d'une instabilité de digitation visqueuse à cette instabilité de digitation élastique dans un fluide viscoélastique de Maxwell, ce qui ouvre peut-être des perspectives intéressantes dans certains processus morphogénétiquesSystematic experiments have been performed in purely elastic polyacrylamide gels in Hele-Shaw cells. We have shown that a bulk fingering instability arises in the highly deformable confined elastomers. It shares some similarities with the famous Saffman-Taylor instability. In particular, the total adhesion of the elastomer to the glass plates implies a non-gliding condition, crucial for the formation of fingers. However, adhesion does not enter the total energy balance, which is shown by the independence of the instability onset from the shear modulus. A systematic study also shows that surface tension is not relevant either. This instability is sub-critical, with a clear hysteretic behavior. Our experimental observations have been compared very favorably to theoretical and finite element simulations results. In particular, the instability wavelength and the critical front advance have been shown to be proportional to the distance between the two glass plates constituting the cell. We have also shown that in Maxwell viscoelastic fluids, one crosses over continuously from a viscous to an elastic fingering instability. These experiments open interesting perspectives in morphogenesis
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Rodrigues, Jeffrey Collin. "Comparison of shear stability of mini and macroemulsion latexes with respect to particle size and number distribution." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/9136.
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Herman, David Joel. "Stabilization of weakly charged microparticles using highly charged nanoparticles." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/34345.
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An experimental investigation was conducted to evaluate the possible use of highly-charged spherical nanoparticles to stabilize an aqueous dispersion of weakly-charged microspheres. At low pH values, the surface of silica is weakly charged, which leads to flocculation of colloidal suspensions of silica microspheres. Binary solutions of weakly charged silica microspheres and highly charged polystyrene latex nanoparticles result in adsorption of the nanoparticles onto the surface of the silica microspheres. This effectively â rechargesâ the silica spheres, with effective zeta potentials increased to the range that is unfavorable for flocculation of microspheres in a silica-only solution. However, this does not guarantee stability, and comparisons between positively charged amidine latex nanoparticles and negatively charged sulfate latex nanoparticles indicate that the degree of coverage plays an important role in the restabilization. The sulfate latex nanoparticles do not cover the surface sufficiently, and though they seemingly provide sufficient charge, the weakly charged patches of the exposed silica substrate can lead to flocculation. The amidine latex nanoparticles, on the other hand, cover the surface more completely, and effectively prevent flocculation of the silica microspheres. The mechanisms responsible for this different adsorption and stabilizing behavior are not entirely understood, as both the amidine and sulfate latex nanoparticles are of similar size and the magnitude of the zeta potentials of the different particle types are comparable.Master of Science
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Fall, Andreas. "Colloidal interactions and orientation of nanocellulose particles." Doctoral thesis, KTH, Fiberteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133941.
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Nanoparticles are very interesting building blocks. Their large surface-to-bulk ratio gives them different properties from those of larger particles. Controlling their assembly can greatly affect macroscopic material properties. This often happens in nature, resulting in macroscopic materials with properties far better than those of similar human-made materials. However, in this fast-growing research field, we may soon compete with nature in certain areas. This thesis demonstrates that the distribution and orientation of nanocellulose particles can be controlled, which is crucial for many applications. Nanocellulose is an interesting nanoparticle, for example, because of its high strength, low thermal expansion, and high crystallinity. Nanocellulose particles are called nanofibrillated cellulose (NFC) or cellulose nanocrystals (CNCs). NFC is obtained from wood by mechanically shearing apart fibrils from the fiber wall and to obtain CNCs, parts of the cellulose are broken down by hydrolytic acidic reactions, most commonly, prior to homogenization. NFC particles are longer and less crystalline than are CNCs, but both are similar in width. The particles attract each other in aqueous dispersions and have a high aspect ratio and, thus, a large tendency to aggregate. The rate at which this occurs is typically reduced by charging the particles, generating an electrostatic repulsion between them. To fully utilize the many interesting properties of nanocellulose, the aggregation and orientation of the particles have to be controlled; examining this delicate task is the objective of this thesis. The limits for particle stability and aggregation are examined in papers 2–3 (as well as in this thesis) and orientation of the particles is investigated in papers 3–5. In addition, the liberation of the nanoparticles from different types of wood fibers is studied in papers 1 and 2. It was found that the liberation yield improved with increased fiber charge. In addition, the charge of the fibrils is higher than the charge of the original fibers, indicating that the fibrils were liberated from highly charged parts of the fibers and that the low-charge fraction was removed during processing. Aggregation was both theoretically predicted and experimentally studied. A theoretical model was formulated based on Derjaguin–Landau–Verwey–Overbeek theory, which is intended to predict the influence of salt, pH, and particle charge on the colloidal stability of the NFC. To predict the experimental trends, specific interactions between salt counterions and the particles charges had to be included in the model, which greatly increased the effect of salt on the NFC stability. Below the particle overlap concentration, instability induced by pH or salt created small sedimenting flocs, whereas above the overlap concentration the system gelled. Increasing the particle concentration further also gels the system. Orientation of nanocellulose was first achieved by shearing, salt- or acid-induced NFC gels. This oriented the fibrils and increased the gel modulus in the direction of shear. The orientation persisted after the shear strain was released and did not cause breakdown of the macroscopic gel. The orientation is probably due to rotation in the interfibril crosslinks, which is possible because the crosslinks are physical, not covalent. Second, orientation was also induced by elongational flow. Shear and acceleration forces were combined to align fibrils in the direction of the flow. The orientation was then frozen by gelation (adding salt or reducing the pH). Drying the gel threads created filaments of aligned fibrils with a higher specific strength than that of steel. Finally, CNC particles could be aligned on flat surfaces. The particles were first forced to align due to geometrical constraints in grooves on a nanowrinkled surface. The CNCs were then transferred to a flat surface using a contact-printing process. This created surfaces with lines of highly aligned CNCs, where the line–line spacing was controlled with nanometer precision.QC 20131114
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Bean, Keith Howard. "Stability studies of colloidal silica dispersions in binary solvent mixtures." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251536.
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Dong, Liang-Chang. "Thermally reversible hydrogels for controlled drug delivery and enzyme immobilization /." Thesis, Connect to this title online; UW restricted, 1990. http://hdl.handle.net/1773/8009.
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Laurens, Gaétan. "Laser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1161/document.
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L’engouement pour l’originalité des propriétés physiques des nanoparticules s’est accompagné d’un développement de nombreuses méthodes de synthèse depuis un demi siècle. Parmi elles, l’ablation laser en liquide permet de produire des nanoparticules avec des surfaces libres de tout contaminant et ce pour une multitude de combinaisons de matériaux et de solvants. Cependant, la simplicité apparente de cette technique dissimule la complexité des mécanismes physico-chimiques, ce qui entraîne actuellement un manque de contrôle des objets synthétisés. Tout d’abord, nous nous sommes intéressés à la cinétique des bulles pour laquelle les conditionsextrêmes d’ablation laser en liquide présentent des cas originaux de cinétique dans le domaine de la mécanique des fluides. Puis, ce travail de thèse vise à donner de plus amples perspectives quant à une meilleure maîtrise de la structure cristalline des nanoparticules et de la stabilité colloïdale. Une manière plus directe de contrôler la taille, la phase cristalline et la stabilité colloïdale des solutions contenant des nanoparticules est d’ajouter des ligands. Nous avons donc étudié les mécanismes de stabilisation de ces solutions en utilisant des ions qui se complexent aux nanoparticules d’or. Nous avons aussi réussi à synthétiser des nanoparticules de rubis (alumine dopée chrome). La stabilisation de ces nanoparticules dans une phase métastable en utilisant des ligands organiques a été expliquée par une étude théoriqueLaser generation of nanoparticles in liquids : new insights on crystal structure control and colloidal stability The great interest of nanoparticles for their original physical and an chemical properties has been supported by the development of numerous methods of synthesis. In the nineties, laser generation of nanoparticles in liquids appeared, including Pulsed Laser Ablation in Liquids (PLAL). The PLAL technique enables to produce surface free particles for plenty of material and solvent combinations. However, the apparent simplicity of its implementation hides complex physico-chemical mechanisms resulting in a lack of control of the final products. We firstly investigated the dynamics of the laser-generated bubbles for which the PLAL extreme conditions present new studied cases of bubbles dynamics not encountered in the field of fluid mechanics. Then, we aim to bring new insights into better control of the nanoparticles morphology and their colloidal stability. A straight way to tune sizes, crystal structures and the colloidal stability consists in the addition of stabilizing agents. Hence, we investigated the mechanisms of stabilization of colloidal gold using complexing ions. We also succeed to synthesis nano-rubies, i.e. chromium doped corundum alumina nanoparticles, unexpected at nanoscale. The stabilization of the metastable crystal structure using ligands is explained thanks to a comprehensive theoretical approach
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Thwala, Justice M. "Dispersion stability of inorganic colloidal particles in media of intermediate polarity." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261280.
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Ji, Shunxi. "Forces and Stability in Ternary Colloidal Systems: Evidence of Synergistic Effects." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/47803.
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Understanding and controlling the forces between colloidal particles in solution, along with the resulting stability of a dispersion of such particles, continues to be at topic of great interest. Although most laboratory studies focus on model systems in which the number of system species is kept to a minimum, real colloidal systems can be much more complex, consisting of multiple components that can vary greatly in size, charge, shape, etc. This dissertation focused on a topic that has received very little prior study, namely synergistic effects that can arise in mixed colloidal systems in which the resulting force and stability of the system cannot be predicted using results obtained in more idealized systems consisting of fewer components.
Two specific systems were studied. The first was a ternary system of particles in which micron-sized particles were in a dispersion containing both nanoparticles and submicron particles. It was shown through both computation modeling and direct force measurements that the nanoparticles can create attractive forces between the micron and submicron particles such that a halo of submicron particles is formed. This halo results in long range forces between the microparticles that cannot be predicted from measurements in systems containing only nanoparticles or only submicron particles. In addition, the forces can be large enough to alter the stability of a dispersion of these microparticles.
The second system consisted of microparticles in a solution containing nanoparticles and a polyelectrolyte, specifically poly(acrylic) acid. Again, through modeling and experimentation, it was found that complexation of the nanoparticles and polyelectrolyte molecules led to depletion and structural forces between the microparticles that were substantially greater than the sum of the forces measured in systems of only nanoparticles or only polyelectrolyte. It was also found that these greater forces could lead to destabilization of a dispersion of microparticles that was stable when only nanoparticles or only polyelectrolyte was present.
While these results clearly demonstrate the difficulty associated with predicting forces and stability in mixed colloidal systems, they also indicate that such systems offer new and interesting opportunities for controlling stability that clearly warrant additional study.Ph. D.
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Mateos, González Eduardo. "Measurement of stability and size of colloidal particles in aqueous suspension." Thesis, Uppsala universitet, Materialfysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394083.
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This project focused on the study of self-assembling systems that can be inuenced by an external magnetic field, following the PhD research of Hauke Carstensen. My role was to study the behavior of beads and to optimize the tunable parameters so that the main force driving the dynamics of the system is the magnetic dipolar interaction between beads. To make sure that no other force plays an important role, we checked a number of things, the most problematic of which is flocculation in the colloid, which may happen if some beads get stuck to each other; to prevent them from aggregating we have to make sure that they have a large zeta potential, which will result in an electrically repulsive force between beads and will thus increase the stability of the colloid. We also have to make sure that other forces in the sample do not exceed the magnitude of magnetic forces between particles; examples of such forces can be the drag experienced while moving in the viscous ferrofluid, the gravity force or the random thermal movement of the molecules in the fluid. In order to study these efects, I measured the zeta potential of the magnetic and non-magnetic beads and later I added a surfactant compound (SDS) to our sample in order to increase said potential.
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Jiang, Canlan [Verfasser]. "Characterization and stability investigation of water dispersible colloids (WDCs) in natural soils / Canlan Jiang." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1044951818/34.
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Palla, Byron Joseph. "Mixed surfactant systems to control dispersion stability in severe environments for enhancing chemical mechanical polishing (CMP) of metal surfaces." [Florida] : State University System of Florida, 2000. http://etd.fcla.edu/etd/uf/2000/ana6408/byronpalla.PDF.
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Thesis (Ph. D.)--University of Florida, 2000.Title from first page of PDF file. Document formatted into pages; contains xvii, 174 p.; also contains graphics. Vita. Includes bibliographical references (p. 165-173).
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Guéry, Julie. "Emulsions doubles cristallisables : stabilité, encapsulation et relargage." Paris 6, 2006. http://www.theses.fr/2006PA066272.
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Ce manuscrit présente l’étude de la stabilité et des propriétés d’encapsulation et de relargage des émulsions doubles cristallisables. Notre démarche a été de remplacer l’huile liquide classiquement utilisée pour les émulsions doubles par une huile solide à température ambiante. Une barrière répulsive stérique assure la stabilité de ces objets au repos. Sous écoulement, les objets s’agrègent : l’énergie fournie par le cisaillement réduit la barrière répulsive alors comparable à kT et facilement franchissable. Ceci se traduit par une dépendance exponentielle du temps caractéristique d’agrégation avec le taux de cisaillement. Sous régime iso-osmotique, la nature solide de la membrane ralentit les cinétiques de libération par diffusion des espèces initialement encapsulées. Sous régime hypo-osmotique, le matériau solide libère rapidement l’espèce encapsulée. Les processus mis en jeu et les différents paramètres permettant de contrôler les cinétiques de libération ont été identifiés.
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Freitas, Alexandre Mussumeci. "Role of acid-base interactions in colloid adhesion and stability of aqueous thin films /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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James, Gregory Keith. "Investigation of Hydrodynamic and Depletion Interactions in Binary Colloidal Dispersions." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24764.
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Within a colloidal dispersion, the presence of negatively adsorbing material can produce a variety of effects on the dispersion properties and interactions. With increasing concentration, the negatively adsorbing material induces both depletion and structural forces on the dispersion, which can dramatically affect both colloidal stability and near-contact hydrodynamics. This project focused on expanding our understanding of the effects of such negatively adsorbing materials on both equilibrium and dynamic interactions between particles.
The effects of charged, hard spheres (silica nanoparticle) on the hydrodynamic drag force a particle experiences as it approaches a flat plate were measured experimentally using colloid probe atomic force microscopy (CP-AFM). Deviation was found between the measured drag force and predictions for the drag force in a simple, Newtonian fluid. The measured drag force was always smaller than the predicted drag force as the particle approached contact with the plate. An effective viscosity, that approached the dispersing fluid viscosity at contact and the bulk viscosity at large separations, was determined for the system. This effective viscosity displayed similar characteristics to those predicted theoretically by Bhattacharya and Blawzdziewicz (J. Chem. Phys. 2008, 128, 214704.).
The effects of both anionic and cationic micelles on the depletion and structural forces in a colloidal dispersion were studied both experimentally (with CP-AFM) and theoretically. The depletion and structural forces between a microparticle and a flat plate were measured and compared with the depletion force predicted by the force-balance model of Walz and Sharma (J. Colloid Interface Sci. 1994, 168, 485-496.). Consistent with previous work, the measured depletion force for both micelles was smaller in magnitude than that predicted by the Walz and Sharma model for hard, charged spheres. It is theorized that rearrangement of the micelle surfaces charges or physical deformation of the micelles may be responsible for the observed result. An effective surface potential for the micelles is proposed as a correction to the Walz and Sharma model.
Finally, the stability of colloidal dispersions was studied macroscopically in solutions of ionic micelles. The colloidal dispersions displayed clear flocculation behavior in both cationic and anionic micelles. This flocculation behavior was compared with energy profiles determined from CP-AFM experiments between a single particle and a flat plate. A simple phase diagram was proposed for predicting the stability of colloidal dispersions based solely on the depth of the depletion energy well and the height of the repulsive energy barrier.Ph. D.
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Mattsson, Rosa. "AKD sizing - dispersion colloidal stability, spreading and sizing with pre-flocculated dispersions /." Licentiate thesis, Luleå tekniska universitet, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17236.
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Alkylketene dimer, AKD, dispersions are used in the paper industry to obtain paper grades with a hydrophobic character i.e. resistance to sorption of water. AKD is used in neutral to alkaline internal sizing, pH in the interval of 6-9. AKD dispersions consist of wax particles emulsified in water. The particles are electrostatically and in most cases also sterically stabilized by cationic polyelectrolytes. The size of the particles is usually in the range of 0.5-2 µm in diameter. The idea of having cationic particles is that they are supposed to be deposited onto the negatively charged fiber surfaces, heterocoagulation. An increased usage of recycled pulp and a closure of the wet-end circuits of the paper machine will lead to increasing levels of dissolved and colloidal substances. These substances could be detrimental by affecting the AKD deposition onto the fiber material and the colloidal stability i.e. induce flocculation of sizing particles. Flocculation could lead to an inhomogeneous distribution of the sizing agent. The aims addressed in this thesis were the following: to investigate if high levels of shear, electrolyte concentration, anionic polymers and surfactants could affect the colloidal stability and induce flocculation of differently designed AKD dispersions to study the migration of AKD and the influence of extractives on the migration to study the sizing efficiency and retention using flocculated dispersions The colloidal stability of the dispersions was tested under shear by measuring the particle size distribution and the microelectrophoretic mobility. The migration of AKD through paper sheets with defined thickness and through paper sheets impregnated with extractives was analyzed with contact angle measurements on stored samples. The sizing efficiency of flocculated AKD was determined by measuring 60-second Cobb and contact angles on laboratory sheets. The retention of AKD was determined by quantitative analysis of the AKD content in the laboratory sheets using alkaline hydrolysis followed by solvent extraction and quantification with capillary gas chromatography. It was shown that anionic polymers and surfactants could seriously affect the colloidal stability of the dispersions, while shear and electrolyte concentration had a small influence. Dispersions with a high surface charge flocculates easier than dispersions with a low surface charge in process water from the wet-end of a linerboard paper machine. The flocculation rate is fast and occurs on the same time scale as deposition onto fines and fibers. The AKD agglomerates could be up to 30 µm in diameter even at high levels of shear. The AKD diffusion coefficient in paper sheets was estimated to be 10-11 m2/s at a temperature above the melting point of the wax. The results indicate that extractives do not interfere with the AKD migration. A reasonable explanation is that migration occurs via the vapor phase. It was also shown that sizing with flocculated AKD improved the sizing efficiency significantly due to increased retention. This clearly indicates that migration is efficient and that agglomerates can be used for internal sizing provided that the flocculation process is controlled. The conventional picture that the sizing agents must be very evenly distributed to achieve efficient sizing could, from the viewpoint of these results, be questioned. The process of sizing with pre-flocculated AKD dispersions is the subject of a patent application. Even if this thesis is focused on AKD dispersions, the obtained knowledge should be possible to transfer to other sizing systems. The emulsification process for rosin and ASA is based on the same principles as for AKD.Godkänd; 2002; 20070222 (ysko)
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Rebodos, Robert Louie Fermo. "Implications of Oxidation on the Colloidal Stability of Magnetite Nanoparticles and Cluster." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77117.
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Synthetic nanomagnetite has been suggested as a potential reactant for the in-situ treatment of contaminated groundwater. Although the application of nanomagnetite for environmental remediation is promising, a full understanding of its reactivity has been deterred by the propensity of the nanoparticles to aggregate and form clusters. To characterize the factors responsible for this aggregation behavior, we determined the magnetic properties of magnetite using a superconducting quantum interference device (SQuID). Importantly, because magnetite readily reacts with O2 to produce maghemite, we analyzed the effect of oxidation on its magnetic properties. We observed that oxidation caused a decrease in the saturation magnetization and the anisotrophic barrier of magnetite resulting in less significant magnetic interactions between particles. Consequently, a decrease in the aggregation of magnetite clusters and a potential increase in stability are expected after oxidation. To support these findings, an extended series of experiments to measure the aggregation and the sedimentation of clusters of unoxidized and oxidized magnetite nanoparticles were conducted. Although the individual particle diameter remained constant after oxidation, the cluster size and the aggregation and sedimentation kinetics of magnetite were determined to be different. Oxidized samples of magnetite tended to have lower aggregation rates and were more resistant to sedimentation. These findings can be used to have a better understanding of the overall fate, transport, and reactivity of nanomagnetite, and to gain new insights on its role as a remediation agent in the subsurface environment.Ph. D.
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GHERARDI, BETTY. "Organisation multiechelle et stabilite colloidale de suspensions d'argiles organophiles en milieu organique." Orléans, 1998. http://www.theses.fr/1998ORLE2010.
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L'etude de la stabilite colloidale de suspensions d'argiles organophiles en milieu organique pose le probleme de comprehension de l'organisation a differentes echelles en phase liquide du systeme colloidal considere. Le systeme mixte choisi se compose de deux colloides lamellaires charges : d'une argile de la famille des smectites, la montmorillonite et de tensioactifs cationiques, les ammoniums quaternaires monocatenaires et bicatenaires. Le travail accompli a mis en oeuvre un ensemble de techniques de caracterisation (dpax, ir, potentiel zeta, met et rheologie). Nous avons montre d'une part, que la redispersion des argiles quaternarisees dans un solvant organique, de faible constante dielectrique depend tres fortement de la mise en place de la couche d'adsorption qui s'effectue au prealable en phase aqueuse. La formation de cette couche adsorbee s'est averee tributaire du mode de preparation choisi et de la quantite de tensioactif adsorbee. Nous avons montre d'autre part, que l'adsorption a l'interface solide-liquide de tensioactifs cationiques ne se fait pas de maniere homogene mais genere plutot des materiaux interstratifies irreguliers dans lesquels coexistent differentes distances caracteristiques, liees aux differentes conformations adoptees par les molecules adsorbees. La couche d'adsorption ainsi constituee en phase aqueuse persiste apres sechage et lors de la redispersion de ces systemes en phase organique. La stabilite colloidale est tributaire de la nature du tensioactif et de son aptitude a espacer les feuillets, du taux de recouvrement de l'argile, de la nature du solvant de redispersion et de celle du solide argileux. Pour des conditions particulieres que nous avons determinees, les suspensions d'argiles organophiles s'organisent en reseaux interconnectes a toutes les echelles, allant de l'echelle micrometrique a l'echelle nanometrique et presentent un comportement de gels viscoelastiques thixotropes.
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Dufrechou, Marie. "Les instabilités protéiques des vins blancs : étude des mécanismes physico-chimiques impliqués dans l’agrégation." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20109/document.
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En œnologie, la formation de trouble d'origine protéique dans les vins blancs est un défaut visuel inacceptable d'un point de vue commercial. Il est attribué à des modifications lentes de la conformation des protéines (présentes à une concentration de 15 à 330 mg.L-1), conduisant à des phénomènes d'agrégation. Ce phénomène est accéléré par une exposition du vin à des températures élevées pendant le transport ou le stockage. Il peut aussi se développer dans des conditions de stockage conventionnelles mais suivant des cinétiques très lentes (> 12 mois). Il est aussi influencé par la composition du vin en ions, polyphénols et polysaccharides. Pour éviter ce problème, des tests et traitements efficaces mais non spécifiques sont appliqués avant embouteillage. Il en résulte une diminution de la qualité organoleptique du vin ainsi qu'une perte non négligeable de produit.L'objectif des travaux présentés dans cette thèse est de progresser dans l'identification des mécanismes physico-chimiques impliqués dans le développement de troubles protéiques. Pour cela, les expérimentations ont été réalisées sur des systèmes modèles et des systèmes réels (vin) dans différentes conditions de température, pH et force ionique. Les résultats ont permis de mettre en évidence les protéines impliquées dans le trouble ainsi que le rôle déterminant du pH et de la force ionique sur les mécanismes d'agrégation, les caractéristiques des agrégats et le trouble final. Les polysaccharides du vin modulent le phénomène d'agrégation mais ne le préviennent pas. Par ailleurs, des modifications de la conformation des protéines du vin induites par le pH ont été mises en évidence. Ces résultats permettent d'apporter des informations supplémentaires pour le développement de tests et de traitements alternatifs plus spécifiquesIn enology, the haze formation in white wine is a visual defect, related to the presence of proteins. This problem is inacceptable for the consumer. It is attributed to a slow unfolding of protein conformation (in white wine at a concentration ranging from 15 to 330 mg.L-1), leading to their aggregation. This phenomenon is accelerated by an exposure to excessive temperature during the storage or the transport. It can also develop on conventional storage conditions but following very slow kinetics (> 12 months). It is influenced by the wine composition in non proteinaceous compounds such as ions, polyphenols and polysaccharides. To prevent this problem, some tests and treatments are used before bottling. However, even if they are efficient, they are non specific to proteins and lead to a diminution of wine organoleptic quality and a non negligible loss of product. The aim of this work is to progress on the identification of physico-chemical mechanisms involved in aggregation. To this end, experiments were performed on model systems and wine, at different conditions of temperature, pH, ionic strength. Results evidenced that specific wine proteins were involved in haze formation whereas others were not. The main role played by pH and ionic strength on aggregation mechanisms, aggregates characteristics and final haze was highlighted. The impact of wine polysaccharides was studied. They modulated the aggregation phenomenon but did not prevent it. Moreover, conformational modifications induced by low pH of some wine proteins were highlighted. These results give some supplementary information for the development of news tests and treatments alternatives, more specific
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Alhassan, Saeed M. "COLLOIDAL INTERACTIONS AND STABILITY IN PROCESSING, FORMATION AND PROPERTIES OF INORGANIC-ORGANIC NANOCOMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301326975.
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Costamagna, Federica. "Colloidal stability, intracellular fate and toxicology of drug nanocarriers - Application to polymerized micelles and organometallic nanogels Nanotoxicology at the particle/micelle frontier: influence of core-polymerization on the intracellular distribution, cytotoxicity and genotoxicity of polydiacetylene micelles." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS128.
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Une compréhension approfondie de la stabilité colloïdale est nécessaire pour concevoir des nanoparticules pour la vectorisation de molécules actives. En particulier, prévoir le comportement in vivo des particules (désagrégation ou agrégation) est fondamental pour prédire l’efficacité et la toxicité des nanoformulations. Les objectifs de cette thèse concernaient (1) l’amélioration de la stabilité colloïdale en conditions physiologiques et (2) l’étude in vitro du comportement biologique de deux types de nanovecteurs : nanogels à base de chitosane-fer et micelles de polydiacétylèneA thorough understanding of the colloidal stability is important to design nanoparticles for drug delivery purposes. In particular, anticipating the in vivo particles disassembly or aggregation is fundamental in order to predict efficacy and toxicity of the nanoformulations. The objectives of this thesis concerned (1) the improvement of the colloidal stability in physiological conditions and (2) the in vitro investigation of the biological behavior of two types of drug nanocarriers: chitosan-iron based nanogels and polydiacetylene micelles
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Heidmann, Ilona. "Influence of fulvic acid on ion binding and colloidal stability of kaolinite particles /." [Zürich], 2004. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15531.
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Lee, Kwang Jik. "Study of stability of ZnO nanoparticles and growth mechanisms of colloidal ZnO nanorods." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4303.
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After hydrolyzing zinc acetate in methanol solution, spherical ZnO nanoparticles in the
size range from about 2.5 to 5 nm were synthesized by maintaining a ZnO concentration
of 0.02M. Compared to ZnO nanoparticles prepared via other methods, the particles
prepared using our novel colloidal chemistry exhibit narrow size distribution and a high
sensitivity to the surrounding environment. The structure and composition of the white
powders precipitated from the colloidal solution can vary, depending on how the powder
samples are prepared. Factors such as desorption and adsorption of methanol, binding of
water and exposure to humid air have been studied to correlate to the structure and
composition observed from the precipitated powder. Methanol desorption rate and
excess KOH on the particle surface have played an important role in the structural
changes. Furthermore, upon annealing, the white precipitate is recovered to wurtize ZnO.
XRD and TEM are used to study the structural transformation of ZnO nanoparticles.
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Pichot, Roman. "Stability and characterisation of emulsions in the presence of colloidal particles and surfactants." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3271/.
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The stability against coalescence of vegetable oil-in-water “food grade” emulsions in the presence of both surfactant and colloidal particles (hydrophilic silica) has been studied and compared to the stability of systems where only the surfactant or the colloidal particles act as the emulsifier. No attempt was made to stop the emulsions from creaming. Two types of surfactants were selected; those that have the ability to stabilise O/W emulsions on their own (O/W surfactants) and those that cannot (W/O surfactants). Tween 60 and Sodium Caseinate were selected as the O/W surfactants, monoolein and lecithin as the W/O surfactants. These mixed emulsifier systems were shown to induce long-term emulsion stability against coalescence, regardless of the surfactant type, via a synergistic “two-part” mechanism in which both the surfactant and colloidal particles components have specific functions. Nonetheless, the emulsion microstructure was proved to depend on the surfactant’s type and concentration: the use of O/W emulsifiers above a certain concentration induced a displacement of particles from the interface, while such a displacement was not observed using W/O emulsifiers. Further measurements of interfacial tension and contact angle showed that the level of adsorption of solid particles at the interface depended on the surfactant type and concentration.
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Pate, Mary Francis. "Coating of NZVI Particles With Modified Starch: Colloidal Stability and Nitrate Reduction Studies." Thesis, North Dakota State University, 2015. https://hdl.handle.net/10365/27816.
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Nanoscale-zero valent iron (NZVI) is an effective groundwater remediation media because it can quickly reduce and absorb contaminants. However, NZVI quickly agglomerates in aqueous systems, reducing its remediation capacity. This work investigated coating NZVI with native and modified rice, wheat, maize, and tapioca starches to improve colloidal stability. Colloidal stability studies were conducted with native and commercially available starches; tapioca starch modified with 2-Octen-l-ylsuccinic anhydride (OSA) was the best. Four concentrations of OSA-tapioca starch were prepared (3, 15, 35, and 50% w/w). NZVI coated with 35% OSA-modified tapioca starch (concentration = 10 g L-1) kept 66% of the coated particles suspended after 2 hours (compared to 4% of bare particles, p = 0.000). Bare NZVI reduced significantly more nitrate (20 mg L-1) than coated NZVI (p =0.000). Bare and coated NZVI provided the same nitrate reduction at 40 and 60 mg L-1 (p = 0.939 and p = 0.815, respectively).National Science Foundation (Grant: CMMI-1125674) and the National Science Foundation Graduate Research Fellow Program