Silica of different structures and silica of the same structure but prepared by different surface treatments can be characterized by their apparent viscosity of dispersion in silicone oil

that was determined at a given shear rate and a given volume fraction.From the variation in dispersion visctsity before and after heat ageing in the confined condition it was found that the hydroxyl groups on the surface of silica are responsible for the degradation of polydimethylsiloxane chain. When the hydroxyl groups were replaced with methylsiloxy groups the thermal stability of the system was improved.