Thermal expansivity and bulk modulus of polymer composites: Experiment versus theory

Correlations between the thermal expansivity, α c , and the compressibility, K c , of particulate‐filled polymer melts are explored in terms of two different theories and in connection with experiments. Both theories employed [an interlayer approach based on micromechanics (IM), and a molecular one starting from the statistical thermodynamics of mixtures (MM)] account for the effect of filler‐matrix interactions, viewed as a system‐dependent parameter. The concentration dependences of α c and K c calculated using either IM or MM agree well with experiments on polyurethane and epoxy composites, and it is possible to predict α c based on K c experimentation. In MM this is always true, but in IM it depends on a knowledge of relations between α and K of the constituents. This point remains to be explored further.