Determination of diffusion and mass transfer coefficients during drying of solvent-absorved polymer films

Mass transfer behavior during the drying process of solvent-absorved polyimide films was investigated. Unsteady state mass balances were developed with a modified Fickian diffusion model involving temperature and concentration dependent diffusion coefficient, founded on Vrentas and Duda's hole free volume theory. Concentration profiles, solvent mass residue, and film thickness changes were obtained from numerical solution of mass transfer equations with moving boundary conditions. An interferometer system was used to measure the variation of film thickness during the drying process. Temperature and concentration dependence of diffusion coefficient and mass transfer coefficient were obtained from comparison of experimental observation and theoretical calculation.