SURFACE-DIFFUSION IN MICROSTRUCTURED, ION-EXCHANGE MATRICES - NAFION/NEUTRON TRACK-ETCHED POLYCARBONATE MEMBRANE COMPOSITES

Steady-state rotating disk voltammetry is used to evaluate the flux of redox moieties through composite ion-exchange membranes formed by sorbing Nafion into the cylindrical pores of neutron track-etched polycarbonate membranes. As the diameter of the pore decreases, flux through the Nafion portion of the composite increases, as much as 20-fold over flux through simple Nafion films. A model is presented to interpret these results. Nafion concentrates redox material in the pore by partitioning, and facile transport is supported by surface diffusion along the pore wall, at the interface between the Nafion and the neutron track-etched membrane. Parameters characteristic of transport in bulk Nafion and of transport along the pore walls are identified and evaluated. Surface diffusion can be exploited to enhance flux in microstructured composites, and generic flux maximization schemes are outlined. Interfacial gradients in microstructural matrices can be capitalized upon to facilitate transport.