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 sor bing Nafion into the cylindrical pores of neutron track-etched polycar bonate 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 t hese results. Nafion concentrates redox material in the pore by partit ioning, and facile transport is supported by surface diffusion along t he pore wall, at the interface between the Nafion and the neutron trac k-etched membrane. Parameters characteristic of transport in bulk Nafi on 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. Inter facial gradients in microstructural matrices can be capitalized upon t o facilitate transport.