Structure of silica-filled poly(dimethyl siloxane) gels and solutions

Small-angle neutron scattering measurements are described for poly(dimethyl siloxane) ablutions and gels containing fumed silica filler, swollen in toluene. Contrast variation with solvent deuteration is used, first to determine the density of the silica, and then to distinguish the three different partial structure factors of the filled polymer samples. The concentration of the polymer solution immediately surrounding the filler particles is found to be enhanced over a distance range of about 20 Angstrom, and then depleted beyond this range. The distribution of the filler particles is described by a stretched exponential with an exponent n = 1/3. Comparison of the partial structure factors of the silica and the polymer indicates that less than 10% of the free surface of the filler particles is in contact with polymer.