Diffusion, Conduction and Convection in Synthetic Polymer Membranes

Polymer membranes are classified according to the arrangements and states of the polymer molecules. The expected mechanisms of transport of small molecules in each type of membrane are discussed. Particular attention is paid to gel membranes and to the complex interactions of fluxes which can occur in ion‐exchange gel membranes. The effect of ion‐exchange equilibrium selectivity on these flux interactions is considered in terms of the frictional model of flow in ionic membranes. An extensive set of experimental data on the fluxes through a cation exchange membrane in contact with mixtures of sodium and strontium bromides is analysed. It is shown that interaction of tracer ionic fluxes cannot be determined and that interactions between other ionic fluxes are small but not negligible for co‐ions and counterions present in small amount. The variations of the principal friction coefficients with the equivalent fractions of the counterions in the membrane are found to be consistent with the model proposed for the membrane structure and with the inferences about ionic distributions which may be drawn from data on ion‐exchange equilibria.