Mathematical analysis of factors influencing the skin thickness of asymmetric reverse osmosis membranes

Abstract

The formation of the dense surface skin of asymmetric reverse osmosis membranes is analyzed in terms of a composite process involving solvent diffusion and polymer relaxation. The analysis indicates that films with minimum skin thickness result from (i) rapid polymer relaxation; (ii) strongly concentration-dependent solvent diffusion coefficients. The numerical results are discussed in terms of experimental variables. It indicates great difficulty in producing asymmetric films with extremely thin surface skins. The implications of this finding are discussed. Experimental NMR self-diffusion studies of acetone in cellulose acetate are reported.