The adsorption of polydimethylsiloxane onto silica from the melt

N.m.r. relaxation and diffusion studies of the adsorption of polydimethylsiloxane polymers on silicas have been carried out as a function of particle concentration and polymer molecular weight. The structure of the adsorbed layer can be rationalized by a three-state model comprising bound polymer, polymer entangled or restricted by the adsorbed layer and free bulk polymer. In particular, n.m.r. relaxation and diffusion studies have enabled us to describe these regions quantitatively. At a loading of 10% particles, nearly 90% of the polymer segments in the dispersion have their mobility constrained, though only similar to 10% of these segments belong to chains that are adsorbed. The diffusion of the bulk polymer is also affected by the inclusion of particulates, and the overall mobility is reduced. (C) 1997 Elsevier Science Ltd.