This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing applications and basic concepts of thermophoresis and outlines some of the experimental and theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general theoretical description for thermophoresis is formulated using the theory of non-equilibrium thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution and a bulk contribution, followed by a determination of transport coefficients based on Onsager’s reciprocal relations. It is further shown how the phenomenological expression of the thermophoretic flux can be recovered when the fluid is at steady-state. The results issuing from this description are then discussed and compared to other existing approaches, some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis. Chapter 3 is dedicated to the validation of the introduced theoretical framework by means of computer simulations, using a simulation technique known as multi-particle collision dynamics. More specifically, the dependence of the thermophoretic force on different system parameters is examined and deviations from the theoretical prediction are explained by an advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents steady-state measurements of functionalised colloids in a temperature gradient, showing how the addition of molecular surface groups increases the experimental complexity of thermophoretic motion. The relaxation process behind this steady-state is also studied, to determine how the relaxation speed depends on the applied temperature gradient. In chapter 5, a general conclusion is drawn from the presented work and its implications are briefly discussed in relation to the current state of knowledge. Finally, the discussion is closed with an outlook on remaining challenges in understanding colloidal motion that could be the subject of future research.

Les suspensions de particules colloidales dans des fluides newtoniens sont utilisées dans un grand nombre de secteurs pour leurs propriétés complexes. Ces dernières proviennent de l’interaction entre les forces hydrodynamiques et les forces physico-chimiques interparticulaires. Malgré de nombreuses études dédiées aux comportements des suspensions colloïdales le lien entre propriétés macroscopiques et forces d’interactions est toujours source de discussions. L’objectif de ce travail est de comprendre et caractériser, aux différentes échelles, et à l’aide de différentes techniques expérimentales, le lien entre la floculation des suspensions et quelques grandeurs rhéologiques (module élastique et contrainte seuil) caractérisant leur comportement macroscopique.La diversité chimique, en taille et en forme des constituants des pâtes cimentaires ainsi que la réactivité du système rendant l’étude trop délicate, des suspensions modèles sont utilisées (particules de silice sphériques et broyés en suspension dans de l’eau).Les suspensions colloïdales formulées sont thixotropes, l’évolution des propriétés rhéologiques en fonction du temps est analysée.Pour les deux types de suspensions, on observe que la contrainte seuil et le module élastique augmentent avec la fraction volumique en particules, la force ionique et le temps de repos.Ces deux grandeurs dépendent de la microstructure des suspensions mais décrivent deux réponses distinctes du matériau suite à l’application d’une sollicitation mécanique. Bien que ces grandeurs soient pilotées par la microstructure du matériau il n’y a pas d’évidence qu’elles soient liées l’une à l’autre. Cependant toutes les données G’=f(Tc) se placent sur une courbe unique pour un type de particule et une taille donnée. Ce résultat confirme que le module élastique peut être utilisé comme un paramètre de structuration caractérisant l’influence de la floculation sur la contrainte seuil. De plus nous nous sommes intéressés à l’impact de la taille des particules sur la réponse rhéologique du matériau. Nous observons que la contrainte seuil est proportionnelle à l’inverse de la taille des particules au carré et le module élastique à l’inverse de la taille des particules. Les modèles présents dans la littérature ne prédisent pas la même normalisation par la taille, cela suggère que les interactions interparticulaires contrôlant le comportement macroscopique ne sont pas encore totalement comprises.L’observation des suspensions au repos par microscopie confocale ne révèle pas de réorganisation structurelle dans le temps. Ainsi la thixotropie des suspensions s’explique probablement par l’existence de nano-organisations structurelles. Cependant des différences de structures sont mises en évidence pour des suspensions de formulations éloignées. Une structure primaire dépendant de l’intensité des interactions et de la fraction volumique se forme de manière instantanée une fois que le précisaillement est arrêté. Il s’en suit une évolution des propriétés rhéologiques avec le temps de repos qui est attribuée à des réarrangements très localisés non visibles par microscopie / Suspensions of colloidal particles suspended in a Newtonian fluid are encountered in many fields of daily life or industrial sectors. Complex behavior of colloidal suspensions comes from the interplay between hydrodynamical and several physico-chemical interactions between the particles. Even if a lot of works have been devoted to these topics, the complex relationships between the interparticle forces and the suspension's overall macroscopic behavior are far from being fully understood. This work aims to understand and characterize, at different scales, and through several techniques, the link between the flocculation state and some rheological properties (elastic modulus and yield stress) of colloidal suspensions.As in real system diversity in sizes, shapes, chemical constituents combined with chemical reaction make the system hard to control we work with model suspensions (spherical and crushed silica particles suspended in water).The suspensions being highly thixotropic, we characterize the evolution of their rheological properties (elastic modulus: G’ and yield stress: τc) with time.We observe for both materials that yield stress and elastic modulus increase with volume fraction, ionic strength and resting time.The two quantities G’ and τc depend on the microstructure ie the floculation state but are linked to two different kinds of response when a mechanical loading is apply to the system. Of course, both quantities depend on the flocculation state of the system but there is not clear evidence that these two quantities must be linked one to the other. However all the data G’=f (τc) collapse onto a simple curve for a given type and a given size of particle. This result proves that elastic shear modulus can be used as a “structural parameter” to account for the influence of flocculation on the yield stress.Moreover we focus on the effect of particle size on the measured properties and we observe that the yield stress scales with the inverse of the squared particle size and the elastic modulus with the inverse of particle size. The models existing in literature do not predict this scaling which would suggest that the interactions controlling macroscopic behaviour are still not fully understood.The observations performed with cofocal microscopy do not reveal any structural organisations when suspensions are left at rest. Then thixotropy of suspensions is assumed to be linked to nano scale change in microstructure. But different microstructure are observed regarding the suspension formulation. A primary microstructure is instantaneously formed once preshear is stopped depending on the intensity of interactions and volume fraction. After that the evolution of rheometric quantities with resting time are attributed to very local rearrangement not detectable with microscopy

L’analyse de la stabilité de formulations est primordiale dans de multiples secteurs industriels : pharmaceutique, cosmétique, agroalimentaire… Il existe donc de nombreuses techniques permettant de caractériser la stabilité de solutions colloïdales. Les méthodes les plus communément utilisées reposent sur l’analyse par diffraction de la lumière, comme le Turbiscan, développé par la société Formulaction, qui est un instrument de référence dans ce domaine. Cependant, de par leur principe de mesure, ces techniques ne sont pas suffisamment sensibles pour l’analyse d’échantillons fortement absorbants. Les autres méthodes existantes – l’analyse par ultrasons, par rayons X… - sont quant à elles complexes, requièrent la connaissance de propriétés difficilement accessibles, voire sont insensibles de par leur principe physique aux produits à base de noir de carbone, qui constituent la majeure partie du marché des produits dits noirs. Il existe donc un besoin concernant une méthode de mesure simple et non-intrusive qui permette d’étudier la stabilité de dispersions fortement absorbantes. Nous présentons dans ce manuscrit une nouvelle méthode de caractérisation, basée sur l’interaction entre les ondes électromagnétiques hyperfréquences et la dispersion fluidique à l’étude. Dans un premier temps, une modélisation des capteurs ainsi que de l’interaction entre ondes hyperfréquences et liquide est présentée, afin de comprendre les mécanismes de fonctionnement du système développé et d’en optimiser la sensibilité. Par la suite, nous avons corroboré les résultats de modélisation par des simulations hyperfréquences démontrant la sensibilité de la technique à une variation de permittivité effective du liquide, et par extension à une variation de fraction volumique. Forts de ces résultats, l’intégration du système de mesure complet comportant quatre capteurs a été réalisée puis le fonctionnement de la technique a été validé par mesures de solutions colloïdales modèles. Enfin, le système de mesure a été testé sur diverses dispersions plus complexes, permettant ainsi de valider la capacité de la technique hyperfréquence à caractériser la stabilité des solutions colloïdales, et par extension la stabilité de solutions colloïdales fortement absorbantes. / Stability analysis of formulations is essential in several industrial fields: pharmaceutical, cosmetics, agri-food… Therefore, many technics were developed to characterize the stability of colloidal suspensions. The most commonly used ones are based on light diffraction analysis, such as the Turbiscan developed by Formulaction, which is a reference instrument in the field. Nevertheless, because of the measurement principle, those techniques are not suitable for the analysis of highly absorbing samples. There are several other methods – acoustic measurements, X-rays diffraction spectrometry… - to analyse absorbing samples but they are complex, require a good knowledge of the sample properties or even are not sensitive to carbon based products, due to their physical principle, which constitute the larger part of the black products market. Therefore, there is a need for a new measurement method, simple and non-intrusive, that allows to study highly absorbing solutions stability. In this manuscript, we present a new characterization method, based on the interaction between microwaves and the fluidic dispersion under study. In a first time, a modelling of the sensors and the interactions between microwaves and the liquid will be presented, to understand the working of the developed system and to optimize it. Thereafter, we will corroborate the modelling results with microwave simulations, to demonstrate the sensitivity of the method to a variation of the effective permittivity of the liquid, and so to a variation of the volume fraction. Based on those results, the integration of the whole system, with the four sensors, will be realised and the functioning of the system will be validated by measuring reference colloidal suspensions. Finally, the measurement system will be tested on several complex suspensions, to validate the ability of the microwave method to characterise the stability of colloidal suspensions, and by extension of highly absorbing colloidal suspensions.

To meet the growing energy world demands, and in conjunction, lower CO2 production levels, near zero emission energy sources must be pushed to the forefront as alternatives to fossil fuels. Photoelectrochemical (PEC) cells are a potential alternative to fossil fuels and have recently generated much interest because of their potential to electrolyze water into hydrogen fuel from sunlight. But in order to be competitive with fossil fuels, understanding the mass-transfer limitations in PEC systems is critical. This work focuses on the addressing the mass-transfer limitations in a conceptually novel PEC cell reactor, the Dual Bed Colloidal Suspension Reactor (DBCSR). Mass-transfer correlations for the DBCSR are presented. The correlations are based on experimental data obtained using two fabricated diffusion cells. The working correlation representative of both cells is given. An analysis of the orientation of the gas sparger suggests that the transport phenomena in both cells is not the same, and therefore using two correlations to represent similar systems is justified. An energy analysis is presented that shows that gas sparging is a low energy consumption option to mitigate mass-transfer limitations. Future work is suggested for better understanding the mass-transfer behavior in the DBCSR.

Latex d’Hevea brasiliensis est composé principalement de particules de caoutchouc dont le noyau est constitué de cis-1,4-polyisoprène et la membrane de composés dit non-isoprène. Sa stabilité dans l'arbre est assurée par les charges négatives de la membrane en raison de la présence de protéines et de lipides. Le latex d’Hevea brasiliensis coagule après acidification pour former un gel colloïdal qui est la première étape de sa transformation en caoutchouc naturel.Dans cette thèse, nous avons étudié l’agrégation et la gélification induite par ajout d’un acide et les propriétés des gels obtenus. Pour cela, un latex de caoutchouc naturel commercial constitué par des particules de caoutchouc (1 µm de diamètre), a été utilisée. L'agrégation a été induite par l'hydrolyse d'un composé appelé glucano-delta-lactone (GDL). Cette agrégation a été suivie par différentes techniques basées sur la diffusion de la lumière (turbidimétrie, DWS, SLS). La gélification a été suivie in situ par la rhéologie. Ensuite, les propriétés rhéologiques de gels colloïdaux formés à pH 4 ont été caractérisées dans les régimes linéaires et non-linéaires.La dépendance à la fraction volumique et le pH de l'apparition de l'agrégation ont été observée. La non-redispersion des agrégats montre les interactions fortes entre les particules de caoutchouc. Trois comportements d’état différents (solution stable, la séparation de phase et gel) peuvent être prédits à partir d'un diagramme d’état fraction volumique-pH qui a été établi pendant 5 semaines. L'état de gel présente une structure fractale, caractérisé par une relation de loi de puissance entre le module élastique G' et la fraction volumique. Pour des fortes déformations, une réorganisation irréversible sous contrainte a abouti à un durcissement irréversible du matériau. Nous avons observé par rheo-ultrasound qu'au-dessus de 50% de déformation, une déstructuration homogène est produite dans le gel. / Natural rubber latex is mainly composed by rubber particles whose core is made of cis-1,4-polyisoprene and the shell of non-isoprene compounds. It stability in the tree is provided by the negative charge of the shell due to the presence of proteins and lipids. Natural rubber latex coagulates after acidification to form a colloidal gel that is the first step of its transformation into natural rubber.In this PhD thesis, we studied this acid-induced aggregation and gelation and the properties of the resulting gels. For this, a commercial natural rubber latex composed by rubber particles (1 µm in diameter), was used. Aggregation was induced by hydrolysis of a compound called glucano-delta-lactone (GDL). The aggregation was followed by different techniques based on light scattering (turbidimetry, DWS, SLS). Gelation was followed in situ by rheology. Then, the rheological properties of colloidal gels formed at pH 4 were characterized in the linear and non-linear regimes.Dependence to the volume fraction and the pH of the onset of aggregation was observed. The non-redispersion of aggregates proves the strong interactions between rubber particles. Three different state behaviors (stable solution, phase separation and gel) can be predicted from a state diagram pH-volume fraction that was established over 5 weeks. The gel state exhibits a fractal structure, characterized by a power law relationship between the elastic modulus G’ and the volume fraction. At high deformations, an irreversible reorganization under stress resulted in an irreversible strain hardening of the material. We observed by rheo-ultrasound that above 50% deformation, an homogenous destructuration occurred in the gel.

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Polymer/inorganic nanoparticle hybrid thin films, primarily composed of functional inorganic nanoparticles, are of great interest to researchers because of their interesting electronic, photonic, and optical properties. In the past two decades, layer-by-layer (LbL) assembly has become one of the most powerful techniques to fabricate such hybrid thin films. This method offers an easy, inexpensive, versatile, and robust fabrication technique for multilayer formation, with precisely controllable nanostructure and tunable properties. In this thesis, various ways to control the structure of hybrid thin films, primarily composed of polyelectrolytes and indium tin oxide (ITO), are the main topics of study. ITO is one of the most widely used conductive transparent oxides (TCOs) for applications such as flat panel displays, photovoltaic cells, and functional windows. In this work, polyethyleneimine (PEI) was used to stabilize the ITO suspensions and improve the film buildup rate during the LbL assembly of poly(sodium 4-styrenesulfonate) (PSS) and ITO. The growth rate was doubled due to the stronger interaction forces between the PSS and PEI-modified ITO layer. The assembly of hybrid films was often initiated by a polyelectrolyte precursor layer, and the characteristics of the precursor layer were found to significantly affect the assembly of the hybrid thin films. The LbL assembly of ITO nanoparticles was realized on several substrates, including cellulose fibers, write-on transparencies, silicon wafers, quartz crystals, and glasses. By coating the cellulose fibers with ITO nanoparticles, a new type of conductive paper was manufactured. By LbL assembly of ITO on write-on transparencies, transparent conductive thin films with conductivity of 10⁻⁴ S/cm and transparency of over 80 % in the visible range were also prepared. As a result of this work on the mechanisms and applications of LbL grown films, the understanding of the LbL assembly of polyelectrolytes and inorganic nanoparticles was significantly extended. In addition to working with ITO nanoparticles, this thesis also demonstrated the ability to grow bicomponent [PEI/SiO₂]n thin films. It was further demonstrated that under the right pH conditions, these films can be grown exponentially (e-LbL), resulting in much thicker films, consisting of mostly the inorganic nanoparticles, in much fewer assembly steps than traditional linearly grown films (l-LbL). These results open the door to new research opportunities for achieving structured nanoparticle thin films, whose functionality depends primarily on the properties of the nanoparticles.

Ce travail de thèse porte sur le développement de nouvelles couches minces nanocomposites par plasma froid à la pression atmosphérique. L'objectif principal est d'améliorer la compréhension des mécanismes physico-chimiques régissant ce procédé de synthèse. La stratégie adoptée est basée sur l'injection via un aérosol d'une suspension colloïdale de nanoparticules d'oxyde métallique dans une décharge à barrière diélectrique opérant en atmosphère d'azote (décharge de Townsend). Dans un premier temps, la synthèse est réalisée de manière séquentielle, la fabrication d'une matrice inorganique de silice (SiO2) étant séparée du dépôt des nanoparticules (TiO2). Ensuite, les couches nanocomposites sont obtenues par un procédé en une seule étape à travers l'injection simultanée dans la décharge des nanoparticules et d'un précurseur polymérisable organosiliciée (HMDSO). Les travaux présentés dans ce manuscrit se divisent en quatre grandes parties : tout d'abord le procédé de fabrication des nanoparticules est présenté, et une étude de leur dispersion dans divers solvants chimiques est réalisée. Puis la deuxième partie s'intéresse à l'étape de nébulisation de la suspension colloïdale, à l'analyse des distributions de taille des objets injectés et à l'étude de leur transport sans plasma. En particulier, une étude de l'influence des principales forces agissant sur leur transport est réalisée. Ces résultats permettent ensuite d'évaluer l'impact de la décharge sur le transport, et sur la réalisation des couches minces nanocomposites. Finalement, l'analyse des propriétés obtenues pour ces couches minces sur des substrats de bois est présentée dans une dernière partie. / This PhD work is focused on the development of a new generation of nanocomposite thin films using cold plasma at atmospheric pressure. The main objective is to improve the understanding of the mechanisms involved in this process.The strategy is based on the injection of a metal oxide nanoparticles suspension in a dielectric barrier discharge operating in nitrogen (Townsend discharge). At first, the nanocomposite thin film is deposited sequentially: the fabrication of the inorganic matrix of silica (SiO2) is separated from the collection of the nanoparticles (TiO2). Then, the nanocomposite layers are obtained by a one-step process using a direct injection inside the discharge of nanoparticles dispersed in a polymerizable organosilicon precursor (HMDSO). This manuscript is divided into four major parts: first, the synthesis of the nanoparticles and the study of their dispersion in different solvents are presented. Then, in the second part we focus on the atomization of the colloidal suspension, on the analysis of the size distributions of the injected objects and on the study of their transport towards the discharge area. These results are then used to assess the influence of the discharge on the transport and the quality of deposited nanocomposite thin films. Finally, the thin films properties are investigated when depositing on wood substrates.

Planetary ball milling (PBM) is a well-known technique for efficient size reduction and homogenization of materials that has been used for many decades in various engineering and industrial processes. More recently, it has emerged as a unique top-down nanofabrication approach for nanomaterials based on nanoscale grinding. However, its potential application in nanostructured thin film fabrication has not been fully explored, as only a limited number of studies have been carried out. In this work, the effects of different grinding parameters (speed, time and solvents) were used to create previously unstudied nanoscale grinding conditions for nanostructured thin film materials via PBM with distinct and novel properties: Nanoparticles of silicon, titanium disilicide (TiSi2) and zinc oxide (ZnO) ground in different solvents (deionized (DI) water/ ethylene glycol (EG)/isopropyl alcohol) resulted in colloidal suspensions (or nanoinks) that could be used to coat various substrates (wafers, glass, flexible substrates, etc.) via drop casting, doctor blading or dip coating. Thin film properties such as wettability, electrical conductivity and gas sensing behavior are studied. The fabricated thin film coating properties could be tuned depending on the combination of starting powder materials, grinding parameters and resulting nanoparticle size/geometry: The influence of surface chemistry, solvent type, particle geometry, surface roughness and defects was shown to alter the conductivity and surface wettability of the resultant films. Thus, thin films formed using PBM nanoinks allow varied and tunable properties for advanced multi-functional coatings and devices. To demonstrate the feasibility of PBM nanoinks for thin film device applications, ZnO nanoinks were used to create chemiresistive gas sensors that operate at room temperature. By varying grinding parameters (speed, time and solvent) thin film sensors with differing particle sizes and porosity were produced and tested with air/oxygen against hydrogen, argon and methane target gas species, in addition to relative humidity. Grinding speeds of up to 1000 rpm produced particle sizes and RMS thin film roughness below 100 nm, as measured by atomic force microscopy and scanning electron microscopy. Raman spectroscopy, photoluminescence and x-ray analysis confirmed the purity and structure of resulting films. The peak gas sensor response was found for grinding parameters of 400 rpm (average particle size 275 nm) and 30 minutes (average particle size 225 nm) in EG and DI water, respectively, which could be correlated to an increased film porosity and an enhanced electron concentration resulting from adsorption/desorption of oxygen ions on the surface of ZnO nanoparticles. Similarly, gas response and dynamic behavior were found to improve as the operating temperature was increased between 100 and 150 °C. These results demonstrate the use of low-cost PBM nanoinks to optimize the active materials for solution-processed thin film gas/humidity sensors that can operate at room temperature for use in environmental, medical, food packaging, laboratory, and industrial applications. Overall, the nanogrinding technique can produce large amounts of nanoparticle suspension with variable particle sizes for creating thin films with tunable properties. By adjusting grinding parameters, the nanoparticle shape/size and properties can be varied resulting in nanoparticle inks for inexpensive coatings on various substrates and for use in different applications. / Graduate

No description available.