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.