Interfacial Events Associated with Case II Diffusion in the Poly(Methylmethacrylate)/CH 3 OH System

Abstract

Surface plasmon (SP) resonance measurements were used to monitor Case II swelling events in the poly(methylmethacrylate) (PMMA)/CH₃OH system on the nanometer-length scale. A simple one-dimensional swelling model effectively correlates measured shifts in SP angular resonance positions to instantaneous film thickness, z, and permeant volume fraction, φ. 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 interpreted in terms of differences in how the elongational viscosity of PMMA depends on temperature. Efflux profiles show evidence of a two-part sample reconstruction process from the rubbery to the glassy state, in which CH₃OH leaves the sample rapidly, followed by a slower return of the PMMA chains to their original density. While interfacial swelling motions appear in general form to mirror those of the macroscopic sample surface, measured interfacial penetrant volume fraction values differ from those measured on the macroscopic-length scale in that they exhibit a substantial dependence on sample temperature.