ELECTRON-MICROSCOPY OF ELASTOMERS CONTAINING INSITU PRECIPITATED SILICA

Transmission electron microscopy is used to characterize reinforcing silica particle precipitated as filler into networks of poly(dimethylsiloxane) by the hydrolysis of tetraethylorthosilicate. Particle diameters were typically 200 A, with relatively narrow distributions. Aggregation is generally very low but, as expected, becomes more pronounced with increase in amount of filler. Acidic catalysts give less well defined particles than basic ones, and large catalyst concentrations give unusually small particle diameters. Permitting the particles to 'digest' in contact with water and catalyst seems to make them better defined, more uniform in size, and less aggregated.