LINEAR VISCOELASTIC DIFFUSION IN THE POLY(STYRENE) ETHYLBENZENE SYSTEM - DIFFERENTIAL SORPTION EXPERIMENTS

Mutual diffusion was studied in the poly(styrene) (PS)/ethylbenzene system using differential vapor sorption. A series of differential sorptions was carried out at 40-degrees-C on a thin film (congruent-to 5 mum) of nearly monodisperse PS (M(n) congruent-to 305 000; M(w)/M(n) congruent-to 1.05). The smallest possible increments in ethylbenzene pressure were used so that very small changes in composition were realized during each sorption. Consequently, the experiments closely approximate a linear perturbation limit. Viscoelastic (non-Fickian) diffusion was observed over the range of ethylbenzene weight fractions 0.03 < omega1 < 0.12. A characteristic sequence of viscoelastic weight uptake curves was found with increasing omega1 in this range; the sequence resembles that found by Odani and co-workers8-11 many years ago. A calculation of diffusion Deborah numbers suggests that relaxation mechanisms associated with both the transition and terminal regions of the linear viscoelastic spectrum play a role in the diffusion process.