Granular polymer composites

Abstract

To advance our understanding of molecular packing in glassy nanocomposites, we adopt a macroscopic granular model—comprising spherical inclusions dispersed in ball-chain polymers—and ascertain from measurements of the bulk density the partial molar sphere volume at small but finite sphere volume fractions. By systematically varying the chain length, sphere size, and mixture composition, the ratio of the sphere radius to the chain loop size was found to be the primary dimensionless parameter that bridges solvent (small inclusion size) and continuum (large inclusion) scaling regimes. In the intermediate regime, where the inclusion and chain loop radius are comparable, the primary sphere–chain interaction increases free volume—up to twice the intrinsic inclusion volume per particle—and the primary sphere–sphere interaction decreases free volume. The results gleaned from these ‘granular nanocomposites’ may help to understand how geometrical constraints influence packing in dense granular systems and glassy molecular nanocomposites.