Permeability of solutes through hydrated polymer membranes. Part I. Diffusion of sodium chloride

Abstract

Based on an analysis by the free volume theory of diffusion, a study of the diffusion coefficients, D 2, the distribution coefficients, κ 2, and the permeability coefficients, P, of NaCl in various hydrophilic polymers was made with the assumptions that the free volume of a polymer/diluent system is linearly proportional to the volume fraction of diluent (H), and that NaCl permeates only through polymer/diluent systems in which the diluent of polymers is also a good solvent of the solute (NaCl). The values of D 2 (over five orders of magnitude) were found to vary exponentially with changes in 1/H, as expected from the free volume theory of diffusion, in a wide range of H‐values and converge to the value of the diffusion constant of NaCl in pure water. The values of κ 2 defined by g NaCl per cm 3 polymer/g NaCl per cm 3 solution were found to be more characteristic to the type of polymers particularly at a lower range of H‐values. At higher ranges of H‐values, k 2 is nearly equal to H, however, at lower H, k 2 values deviate significantly from the value of H and its extent was found to be greatly dependent on the chemical nature of polymers, whereas the diffusion coefficient follows the normal pattern predicted by the free volume theory. The values of P which are given by the product of D 2 and k 2 also were found to vary exponentially with changes in 1/H at higher range of H, however, at lower range of H it deviates from the relationship due to the varying dependence of factor k 2 on 1/H.