18 October 2012
Ion transport and non-equilibrium hysteresis in bipolar membranes - by Richard Craster (joint work with O. Matar, D. Conroy from Imperial College, Chemical Engineering and L. Cheng, H-C Chang from Notre-Dame, Chemical Engineering and Microfluidics Lab)
Some striking, and potentially useful, effects in electrokinetics occur for bipolar membranes: applications are in medical diagnostics amongst other areas. The purpose of this talk is to describe the experiments, the dominant features observed and then model the phenomena: This uncovers the physics that control this process. Time-periodic reverse voltage bias across a bipolar membrane is shown to exhibit transient hysteresis. This is due to the incomplete depletion of mobile ions, at the junction between the membranes, within two adjoining polarized layers; the layer thickness depends on the applied voltage and the surface charge densities. Experiments show that the hysteresis consists of an Ohmic linear rise in the total current with respect to the voltage, followed by a decay of the current. A limiting current is established for a long period when all the mobile ions are depleted from the polarized layer. If the resulting high field within the two polarized layers is sufficiently large, water dissociation occurs to produce proton and hydroxyl travelling wave fronts which contribute to another large jump in the current. We use numerical simulation and asymptotic analysis to interpret the experimental results and to estimate the amplitude of the transient hysteresis and the water-dissociation current.
- Industrial and Applied Mathematics Seminar