Synthesis and application of hybrid organic-inorganic colloidal gels

Aqueous colloidal dispersions of oxide like silica hydrosols are used for many industrial uses [1]. One of them concerns the preparation of ceramic materials. The sol acts as binder or as precursor of mesoporous or densified thin layers by the sol-gel route [2]. These layers can be used, for instance, in optical applications [3] or in membrane processes [4]. The rheological properties of dispersions and the porous texture of aggregates depend on the size distribution of the used particles. Various academic studies deal with bimodal mixtures [5-7] and have shown the strong effect of the size ratio between the coarse and the fine particles on the dispersion and material properties. So it seems interesting to compare these theoretical results with experimental results on colloidal systems which are stable dispersions. Concerning the silica sols, commercial products are available with average particle sizes in the range 10 -30nm. Due to sedimentation, higher particle sizes cannot lead to stable dispersions. The range of particle size ratio is limited and the effects on the rheological and textural properties are reduced [8]. Polymeric latex in another kind of aqueous stable dispersion with a higher particle size ordering, between 0.2 and 2/~m. They are synthesized by the emulsion polymerization technique [9] and are