A computer simulation study on the diffusion and permeation of dimethylformamide/water mixtures through poly(vinyl alcohol)/poly(acrylic acid) blend membranes

Molecular dynamics (MD) simulations were carried out to investigate the diffusion and permeation of dimethylformamide (DMF)/water liquid mixtures through poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) blend membranes. The blend membranes were constructed using various simulation techniques, and were composed of 50% PAA and 50% PVA. The (N, V, T) ensemble and the UNIVERSAL force field were selected to carry out the simulations at 50 °C in a pure water system, and in four liquid mixture systems with increasing mass fractions of DMF. The self diffusion constants and activation energies for the water molecules permeating through the membranes were estimated for all systems. The radial distribution function calculations indicated that H-bonds could be formed between the water molecules and the membrane. With increasing mass fraction of DMF, the ability of water molecules permeating through the membranes decreased. The process of separating water and DMF with the PVA/PAA blend membrane was simulated, and the results showed that the membrane had good hydrophilicity, and DMF was hardly able to permeate through the membrane. The calculated fluxes decreased with increasing mass fractions of DMF, which consisted with the experimental ones obtained with PVA/PAA/ceramic composite membranes; but the calculated flux is beyond one order of magnitude than the experimental flux. The reason for the deviation is probably due to the existence of diffusion resistances in the support of a real polymer/ceramic membrane.