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-particles of fumed silica) using the backscattering spectrometer IRIS at ISIS. Through the analysis of the incoherent scattering, the quasi-elastic neutron scattering (QENS technique probes the motion of the hydrogen atoms and it therefore provides detailed information on the reduced mobility of chain segments in polymer filler systems. QENS measurements reveal a progressive slowing 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 taking into account two contributions: (a) a quasielastic component due to chains not affected by the presence of fillers and (b) an elastic component from chains whose dynamics is strongly restricted. The latter depends on the specific surface area of the particles and their weight fraction in the composites, (C) 2001 Elsevier Science B.V. All rights reserved.