Drying of Glassy Polymer Films

Abstract

During the drying of many polymer films, temperature and compositional changes induce a rubbery−glassy transition at the film surface. The transition front propagates toward the substrate as drying proceeds, eventually rendering the entire coating glassy. The glass transition induces structural changes that have a direct effect on the drying rate. We examine this process by measuring gravimetric and thermal drying profiles for poly(methyl methacrylate) films cast from a toluene-based formulation. The experimental conditions were chosen so that the films would pass through a glass transition. We seek an understanding of the observed behavior by comparing the experimental data to solvent concentration and temperature profiles computed with a mathematical model based on the work of Vrentas and Vrentas.1 The computational results show that the critical factors for capturing the drying behavior of this rubbery−glassy system are (i) the nonideal volumetric behavior exhibited by glassy polymer−solvent systems and (ii) the type of friction-based theory used to relate mutual- and self-diffusion coefficients. The model offers a quantitatively accurate alternative to the many viscoelastic-diffusion-based models that have appeared in the literature.