Elaboration of hybrid materials by templating with mineral liquid crystals stabilization of a mixed sol of YSZ nanoparticles and V2O5 ribbon-like colloids

The purpose of this PhD was to investigate innovative soft chemistry ways to prepare hybrid materials with ordered nano-structures. Concretely, research were conducted on the development of a hybrid material made of an yttria-stabilized zirconia (YSZ) matrix templated by a mineral liquid crystal, namely V2O5. In aqueous solutions, vanadium oxide exhibits ribbon-like colloids of typical dimensions 1 nm x 25 nm x 500 nm, stabilized by a strong negative surface charge. Above a critical concentration, the anisotropic colloids assemble into a nematic liquid crystal, whose domains can be oriented within the same direction over a macroscopic range under a weak magnetic field. The idea is to use V2O5 anisotropic colloids as a template for a hybrid material, taking advantage of their ordering behavior. Preliminary experiments revealed a strong reactivity between molecular compounds of zirconium and vanadium oxide. Therefore, the studies were directed toward the preparation of a mixed colloidal sol containing YSZ nanoparticles and vanadium oxide ribbon-like colloids, as a precursor sol for the intended hybrid material. The YSZ nanoparticles are obtained through an outstanding hydrothermal synthesis leading to a stable suspension of nanocrystalline particles of ca. 5 nm, in pure water. Providing a mixed sol of YSZ and V2O5 is a key challenge for it implies the co-stabilization of two types of colloids having different shape, size and surface properties. Besides, the existence of V2O5 in its ribbon-like form requires acidic conditions and very low ionic strength. The first part of this work was then dedicated to the study of electro-steric stabilization of zirconia suspension by addition of acidic poly-electrolytes. Different polymers with carboxylic and/or sulfonic acidic functions were investigated. Based on zeta potential measurements and adsorption isotherms, the influence of molecular weight and polymer charge were discussed. Among the studied polymers, poly vinylsulfonic acid (PVS) led to stable suspensions which fulfill zeta potential and pH requirements assumed to allow contact with V2O5 colloids. Stable mixed YSZ/PVS/V2O5 sols were then obtained, whose stability limits were discussed. The observations highlighted a probable competition between a depletion effect coming from the mixing of colloids of different size and shape, and the stabilization of a 3D gel network originating from the electrostatic repulsion between V2O5 ribbons. The evaporation of such mixed sols led to hybrid solids whose birefringence revealed an anisotropy caused by the presence of V2O5 ribbons. Various techniques were used to characterize the hybrid material, such as X-ray diffraction and electronic microscopy. (author)