Application of non-equilibrium thermodynamics and computer aided analysis to the estimation of diffusion coefficients in polymer solutions: The solvent evaporation method

In this work, the solvent evaporation method for the estimation of the Fickian diffusion coefficients in binary and in multi-component solvent(s)-polymer systems is reviewed. The existing frameworks for multi-component diffusion are also examined in detail. The described methodology is applied to estimate the diffusion coefficients in the binary systems acetone/cellulose acetate (CA), solvent/poly(vinyl acetate) and in the ternary system water/acetone/cellulose acetate, which is widely used in asymmetric membrane manufacture. The solvent evaporation process from these systems is studied as a one-dimensional numerical experiment. For this purpose, the evaporation process is modeled as a coupled heat and mass transfer problem with a moving boundary. The Galerkin finite element method (GFEM) is used to simultaneously solve the non-linear governing equations. The model predictions are compared with experimental data for polymer solution weight vs. time during evaporation to estimate the unknown parameters of the Vrentas-Duda equation. The estimated diffusion coefficients were found to be in good agreement with those measured by other methods. It is believed that this review might contribute to a more rational design of industrial processes.