Computer-aided estimation of diffusion coefficients in non-solvent/polymer systems

Abstract

Full Paper: A novel method for estimating the mutual and self-diffusion coefficients of a non-solvent/polymer system is proposed in this work. The idea is to stud the evaporation process from non-solvent/solvent/polymer systems as a one-dimensional numerical experiment and to use polymer solution weight versus time data to fit the unknown parameters of the diffusion-coefficient correlations based on free-volume theory. For this purpose, the evaporation process is modeled as a coupled heat- and mass-transfer problem with a moving boundary, and the Galerkin finite-element method is used to solve simultaneously the non-linear governing equations. This method is successfully applied to the estimation of water-cellulose acetate diffusion coefficients and is valid over the whole range of temperatures and concentrations for practical applications in membrane technology. Additionally there is a detailed discussion on if water affects the morphology of the final cellulosic membrane by studying the concentration profiles of the constituents of the casting solution.