EFFECT OF NEUTRAL SILICA PARTICLES ON THE MACROSCOPIC SWELLING AND ELASTIC PROPERTIES OF POLYDIMETHYL SILOXANE NETWORKS

An investigation is reported of the elastic and osmotic properties of end-linked polydimethyl siloxane networks swollen in toluene. These were prepared both in the presence and in the absence of silica filler particles. A comparison is made between the values of the elastic moduli of the unfilled gels, obtained by uniaxial compression experiments and from the concentration dependence of the swelling pressure respectively. For all the gels studied, the elastic modulus was found to vary with polymer volume fraction phi as phi-1/3. The osmotic behaviour can be described by a power law relation in agreement with scaling theory, but cannot be interpreted in a consistent manner by using the osmotic pressure data relevant to the uncrosslinked polymer. For the filled gels, the neutral filler particles produce a reinforcement of the elastic modulus. The concentration dependence of the swelling pressure is affected mainly through the volume occupied by the filler in the network.