Abstract
Polymer membranes, cast from a blend of a polymeric crown ether carboxylic acid and a polyaramid support polymer, were similar in structure to asymmetric membranes prepared from the support polymer alone. In the presence of a transmembrane pH gradient simultaneous cation-proton countertransport and anion-proton cotransport occurs. Rate constants for transport of protons, cations and anions were evaluated under steady-state and non-steady-state conditions and empirical rate equations for the transport process were derived from initial rate experiments under steady state conditions. Cation transport depends upon the cation concentration in the basic phase and the proton concentration in the acidic phase with relative kinetic orders of 1:1. Anion transport depends upon the concentrations of anions and protons in the acidic phase and inversely upon the basic phase cation concentration with relative kinetic orders of 1:1:-2. These results are rationalized by a transport mechanism, rate limited by hopping of ions between adjacent crown ether sites within the membrane. The membrane is essentially non-selective for anion transport but exhibits cation selectivity typical of the crown ether moiety.
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