Silylated filler surfaces

Prior to the chemical reaction of the silane with the silanol-groups on the sUica surface, the silane molecule has to make contact with the sUica surface by adsorption. Then the chemical reaction of silica with an alkoxy-silyl moiety of the coupling agent takes place in a two-step, endothermic reaction. The primary step is the reaction of alkoxy-groups with silanol-groups on the silica filler surface [4]. Two possible mechanisms are reported ... 

Whether the filler surface is hydroxylated or silylated affects the interaction significantly. That is why the substitution of the sxirface hydroxyl groups of as-prepared hydroxylated fumed silica by trimethylsiloxy (TMS) units (surface silylation) is widely used in the silicone industry. 

Fumed silica acts as a highly reinforcing filler in silicone elastomers. Its activity results fi-om its highly dispersed particle structure, high surface area and surface energy. To better understand the interplay of these properties first studies on gas adsorption of hexamethylsiloxane on hydrophilic and silylated silica have been conducted. The shape of the adsorption isotherm revels the existence of low- and high-energy adsorption sites, the latter qualitatively seem to be related to reinforcement of the silicone elastomer. Further quantitative studies in this field are needed. 

BMI-based composites with exceptional mechanical properties were obtained using glass hollow microspheres that were previously submitted to a silane treatment (Koopman et al. 2006). All data indicated that interface adhesion between BMl and filler is strongly affected by the silylation reaction at the glass surface, which enhanced the compatibility. 

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