RELAXATION PHENOMENA IN DENSE, GLASSY MEMBRANES PREPARED FROM A POLYMER-SOLUTION, MONITORED BY CHANGES IN DIELECTRIC-PROPERTIES

The drying of a solvent-cast polymer film is monitored in a non-invasi ve way, by measuring the changes in time of dielectric properties, usi ng interdigitated or comb electrodes. Experimentally, the vitrificatio n of the polymer solution is observed at a distinct time, followed by the slow evaporation of solvent from the glassy state. As the solvent diffusion coefficient is a strong function of the concentration in the polymer film, removal of residual solvent proceeds at a self-decreasi ng rate. With a simple model, solvent mass transfer coefficients in th e glassy state are determined from the experiments. It is shown that v olume relaxation may be slow compared to the drying process, when prep aring thin solvent-cast membranes and using solvents that diffuse rela tively fast through the glassy polymer film.