Restricted dynamics in polymer-filler systems

We have investigated the dynamic properties of poly(dimethylsiloxane) (PDMS ) and poly(vinyl acetate) (PVAc) filled with hydrophilic Aerosil (nano-part icles of fumed silica) using the backscattering spectrometer IRIS at ISIS. Through the analysis of the incoherent scattering, the quasi-elastic neutro n scattering (QENS technique probes the motion of the hydrogen atoms and it therefore provides detailed information on the reduced mobility of chain s egments in polymer filler systems. QENS measurements reveal a progressive s lowing down of the motion with increasing particle surface area which is in agreement with the DMTA data of Tsagaropoulos and Eisenberg. In particular , the QENS spectra of the polymer-filler composites confirmed the existence of two dynamic processes. Therefore, data analysis was carried out by taki ng into account two contributions: (a) a quasielastic component due to chai ns not affected by the presence of fillers and (b) an elastic component fro m chains whose dynamics is strongly restricted. The latter depends on the s pecific surface area of the particles and their weight fraction in the comp osites, (C) 2001 Elsevier Science B.V. All rights reserved.