POLY(DIMETHYLSILOXANE)-SILICA MIXTURES - INTERMEDIATE STATES OF ADSORPTION AND SWELLING PROPERTIES

The properties of poly(dimethylsiloxane)-silica mixtures are studied b y varying the specific area of silica aggregates and the chain molecul ar weight. The specific area was varied either by changing the nature of the silica (50 or 150 ml g-1) or by converting silanol groups into trimethylsilyl groups. It is shown that a single kinetic law applies t o the description of the chain adsorption process after the mechanical mixing, whatever the chain molecular weight and the silica concentrat ion. In contrast with this result, the time constant is found to depen d upon these two variables. Swelling properties of these mixtures were observed in order to investigate statistical structures corresponding to intermediate states of chain adsorption. A quantitative interpreta tion of swelling effects is given within the framework of percolation. It is shown that the mean number of contact points of one adsorbed ch ain with the silica surface is proportional to the square root of the chain molecular weight. This result was shown, in previous work, to ch aracterize equilibrium states of adsorption; it is now extended to int ermediate states of chain adsorption.