STRUCTURAL ARREST AND THERMODYNAMIC SCALING IN FILLER-REINFORCED POLYMERS

The role of small silica particles on the stiffness and glass transition dynamics of polyvinyl acetate (PVAc) was examined for filler volume fraction (phi) from 0 to 0.28. Whereas the influences of bound polymer and a strain-dependent filler network were clearly noted in the shear properties, the only effect of filler on the bulk modulus was the reduction in deformable polymer. The calorimetric glass transition of PVAc and its dependence on cooling rate were unaltered by the presence of the silica, in agreement with previous dielectric relaxation results. In contrast to the temperature dependence of the segmental dynamics, which was independent of phi, the effect of volume on segmental relaxation was amplified by the addition of silica. This resulted in larger values for the thermodynamic scaling exponent (gamma), which also increased sharply at the filler concentration corresponding to the development of a percolated filler network.