Silane coupling agents reaction with filler surfaces

The non-coupling silanes in use are generally quite volatile, and filler coating is often carried out in the gas phase by exposing the filler to their vapours. This ensures maximum reaction with the surface and minimum self-condensation. The silane coupling agents, on the other hand, are less volatile and are usually coated in liquid form, either as neat additives, or from a suitable solvent. 

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 ... 

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