Local dynamics of poly(dimethyl siloxane) in the presence of reinforcing filler particles

The dynamics of poly(dimethyl siloxane) (PDMS) filled with very fine silica particles with surface areas equal to 90 and 300 m(2) g(-1) has been investigated by quasielastic neutron scattering (QENS). The elastic scattering intensity has been monitored as a function of temperature up to 275 K and momentum transfer Q for values corresponding to the first and second sharp diffraction maxima. A small dynamic effect is observed below 235 K, i.e. below the melting temperature of PDMS. Considerable decrease of molecular mobility in the filled systems is detected above 235 K as a result of the decreased entropy of the adsorbed segments. The extent of reduced mobility is such that part of the chains no longer contributes to the quasielastic broadening but gives rise to an elastic component. At 40 wt% silica content and 250 K the fraction of immobilized segments amounts to 0.072 +/- 0.005 for the filler with 90 m(2) g(-1) surface area which corresponds to an adsorption layer of about 50 Angstrom. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.