INTERFACIAL EVENTS ASSOCIATED WITH CASE-II DIFFUSION IN THE POLY(METHYLMETHACRYLATE) CH3OH SYSTEM/

Surface plasmon (SP) resonance measurements were used to monitor Case II swelling events in the poly (methylmethacrylate) (PMMA)/CH3OH syste m on the nanometer-length scale. A simple one-dimensional swelling mod el effectively correlates measured shifts in SP angular resonance posi tions to instantaneous film thickness, z, and permeant volume fraction , phi. Swelling motions in continuous polymer films less than 10 nm in thicknesses are easily resolved. Permeant molecules are incorporated at the PMMA interface by a mechanism consistent with a modified Thomas -Windle (TW) model. Temperature differences in sorption kinetics are i nterpreted in terms of differences in how the elongational viscosity o f PMMA depends on temperature. Efflux profiles show evidence of a two- part sample reconstruction process from the rubbery to the glassy stat e, in which CH3OH leaves the sample rapidly, followed by a slower retu rn of the PMMA chains to their original density. While interfacial swe lling motions appear in general form to mirror those of the macroscopi c sample surface, measured interfacial penetrant volume fraction value s differ from those measured on the macroscopic-length scale in that t hey exhibit a substantial dependence on sample temperature.