Laser interferometry is found to be a very convenient technique for studying gradient diffusion in the poly(methyl methacrylate)/methanol (PMMA/MeOH) system. We studied the process in initially dry, supported PMMA films suddenly immersed in liquid MeOH and examined the effects of temperature and sample thermal history. Over the range of conditions studied, the diffusion process was entirely Case II. A simple model was developed to predict the time dependence of the intensity of light reflected from a supported film during Case II. An FFT algorithm made it possible to accurately match the reflected intensity data and the model predictions to determine the key parameters defining the Case II process: The volume fraction of methanol behind the Case II front (

ABSTRACT:We investigated the effects of polymer molecular weight and temperature on Case II transport in the poly(methyl methacrylate)/methanol (PMMA/MeOH) system by a laser interferometric technique, using monodisperse polymer samples. Both the induction process and the steady-state front propagation were investigated. The data gave the volume fraction of MeOH in the swollen layer behind the moving front, , the steady state front speed, , and the characteristic induction time, t ind . Values of separated into two groups, independent of molecular weight within each group. Significantly lower values of were found for polymers with molecular weight above the critical threshold for entanglement which can be explained by unrelaxed entanglements in the swollen layer. The Case II front velocity was independent of molecular weight for molecular weights at, or above, the critical weight for entanglement, suggesting that anelastic deformation processes other than simple viscous flow control the front propagation. Analysis of induction time data shows that the film surface properties differ from those of the bulk.

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