TRANSPORT PROCESSES IN MEMBRANES CONTAINING NEUTRAL ION CARRIERS, POSITIVE-ION COMPLEXES, NEGATIVE MOBILE SITES, AND ION-PAIRS

The response of membranes, which are prepared with neutral ion carrier s and mobile sites, to an externally applied potential step was invest igated theoretically and experimentally. Two cases were identified: th e first, in which the neutral carriers were in large excess, showed a gradual decrease in the magnitude of transient currents due to the inc rease in bulk membrane resistance. Using digital simulations, this obs ervation was related to the polarization of the concentration profiles of sites and counter ions. The second case showed a behavior limited by the small amount of carrier. A characteristic break in a current vs time plot in this constant-resistance system corresponded to depletio n of the carrier at the interface where the selected ion entered the m embrane. Most of the experimental evidence for both processes was obta ined from plasticized PVC membranes containing valinomycin and tetraph enylborate-type trapped mobile sites. The results support the presence of a carrier mechanism in these systems and illustrate the transport of ions and ion pairs in the membranes as well.