Many materials and biological systems in nature are suspensions composed of disks, such as clay, asphaltenes, and red blood cells. Despite their natural abundance and wide industrial application, disks are least studied compared to spheres and rods, due to the lack of model systems. In our research, disks at micro-scale were mass-produced with unprecedented uniformity in size and shape, and unique flexibility in the control of lateral size, lateral size polydispersity, shape, and aspect ratio (ξ = diameter/thickness). This dissertation focuses on two main areas: the study of the discotic colloidal liquid crystal phase transitions and the application of disk-like colloidal systems as Pickering emulsion and Pickering foam stabilizers. First, we engineered two discotic colloidal systems made from organic and inorganic materials. The former is made of α-eicosene, which is an alkene of 20 carbons. The latter is composed of nano-sheets from exfoliated zirconium phosphate (α-ZrP). Both discotic systems were used to experimentally investigate the liquid crystalline phase transitions (Isotropic-Nematic, Isotropic-Cubic and Isotropic-Columnar). Also, the nematic crystalline phase was studied in detail by embedding it in a translucent and thermo-sensitive hydrogel. This was possible since nematic textures could be formed instantly by ZrP nano-sheets due to their high diameter-thickness ratio. Second, we developed Pickering emulsions and Pickering foams stabilized by high-aspect-ratio nano-sheets. We have also demonstrated for the first time the fabrication of the thinnest amphiphilic Janus and Gemini nano-sheets, which are either surface- or edge-modified plates with a thickness at atomic scale. These nano-sheets were obtained by exfoliating α-ZrP crystals grafted with a coupling agent of hydrophobic molecules on their edges and outer surfaces. Extending this work, we studied crucial fundamental mechanisms that allow Pickering interfacial stabilization, including the effect on the adsorption properties of particle aspect ratio, concentration, and hydrophobicity. Our study is of great interest in the scientific community due to the difficulty in generating a discotic colloidal system of controllable parameters.

Nous décrivons dans ce travail l’élaboration de latex nanocomposites à base d’oxyde de cérium en vue d’applications dans le domaine des revêtements. Deux procédés originaux ont été développés afin de contrôler la morphologie des particules. Dans un premier temps, nous avons tiré parti de la forte densité de charges des nanoparticules d’oxyde de cérium pour stabiliser des particules de latex obtenues par polymérisation en émulsion ou en miniémulsion « de Pickering ». Dans les deux cas, la réaction est conduite en présence des particules inorganiques et d’un agent complexant à caractère acide, l’acide méthacrylique, en l’absence de tout tensioactif. Des particules de latex, décorées en surface par les nanoparticules d’oxyde de cérium ont été ainsi synthétisées. Par la suite, une stratégie qui consiste à utiliser des chaînes de polymères hydrophiles, réactivables (macro-agent RAFT) et préalablement adsorbées à la surface des nanoparticules d’oxyde de cérium a été envisagée. Ces chaînes polymères comportant à la fois des fonctions carboxyliques et un groupe trithiocarbonate terminal sont capables de stabiliser la suspension colloïdale des nanoparticules et de réamorcer la polymérisation en mode semi-continu permettant ainsi l’encapsulation de l’oxyde de cérium. Une optimisation visant à utiliser un procédé batch a également été évaluée. Quelle que soit la stratégie employée, une attention toute particulière a été portée à la stabilité colloïdale du milieu ainsi qu’à la cinétique de la réaction. La morphologie des particules composites a été caractérisée par MET et cryo-MET et reliée aux conditions de modification de surface et de polymérisation / This work describes the elaboration of nanocomposite latexes containing cerium dioxide nanoparticles for coating applications. Two original approaches have been developed to control the particle morphology. First, we took advantage of the high charge density of cerium dioxide nanoparticles to stabilize latex particles obtained via emulsion or “Pickering” miniemulsion polymerization. In both cases the reaction was conducted in the presence of the inorganic particles and methacrylic acid as a complexing agent, in the absence of any added surfactant. Armored latex particles covered with cerium dioxide nanoparticules were obtained by this method. Subsequently, another approach based on the use of living hydrophilic polymer chains (macroRAFT agents) previously adsorbed on the surface of the cerium dioxide nanoparticles was considered. These copolymers both containing carboxylic acid groups and carrying a thiocarbonylthio end group led to stable aqueous dispersion of the nanoparticles and could chain extend to form an encapsulating polymer shell under starved feed emulsion polymerization conditions. An optimization using a batch process was also evaluated. For both approaches, particular attention was paid to the colloidal stability of the medium and to the kinetics of the reaction. The morphology of the nanocomposite latex particles was characterized by TEM and cryo-TEM and correlated with the surface modification and the experimental conditions