The diffusion of solvents in polymers is a controlling process in many product development and process engineering problems. When the polymer is in or near the glassy state, "non-Fickian" diffusion is often seen. At present, there is no widely accepted description of non-Fickian diffusion offering reliable calculations for process or product development. The broad goal of the proposed research, therefore, is to provide such a description. In previous work a theory was developed, for non-Fickian diffusion in the "linear" limit, where the disturbance from equilibrium is very small. A modicum of data was collected which strongly supports the description. In the proposed work, a more comprehensive set of linear diffusion data will be collected using the differential sorption technique. The data will be compared quantitatively with the theory to define its strengths and weaknesses and to enable refinements, if necessary. With a sound linear theory in hand, a reliable nonlinear theory will then follow.
