FREE-VOLUME DISTRIBUTIONS IN AMORPHOUS POLYMERS

A new free volume distribution function for amorphous polymers is derived on the basis of a lattice model. It provides a good description of the non-Gaussian spreading observed very recently in positron annihilation experiments. This new theory shows that the non-Gaussian distribution is a result of the large density fluctuations of holes from their equilibrium. The Gaussian distribution is recovered in the limit of small fluctuations. The size and volume distribution of the holes is uniquely defined by two structural parameters: the energy of hole formation and the lattice volume. Our theory predicts that increases in temperature will broaden the distribution and shift its lower peak to higher free volume. Increases in pressure have the opposite effect.