A MODEL FOR PREDICTING SOLVENT SELF-DIFFUSION COEFFICIENTS IN NONGLASSY POLYMER SOLVENT SOLUTIONS

In this paper, the Cohen-Turnbull diffusion theory is used to develop a model for predicting solvent self-diffusion coefficients D//1 in nonglassy polymer/solvent solutions. Polymer molecules are envisioned as hindering solvent mobility by reducing the average free volume per unit mass in the system and through the lower mobility of polymer segments relative to solvent molecules. The concentration dependence of D//1 predicted by the model is in reasonable agreement with data for the solvents heptane, hexadecane, benzene, cyclohexane, and decalin in polyisobutylene (PIB), and for toluene in polystyrene, poly(methyl methacrylate), and PIB. Although none of the data is for high concentrations of polymer (volume fractions phi //2 greater than equivalent to 0. 9) it is anticipated the model will be less representative in this regime where the assumptions in its development are unsure. The model also demonstrates the correct temperature and concentration dependence of the apparent activation energy for diffusion.