Nonlinear Electrokinetics of Leaky Membranes
Martin Bazant (MIT)
Electrohydrodynamics and electrokinetics of fluid systems
Mon 9:00 - 10:30
Barus-Holley 161
The classical model of an ion-exchange membrane assumes constant conductivity, set by counterions screening the membrane charge. Such a “good membrane” exhibits familiar linear electrokinetic phenomena (Ohmic conduction, streaming potential, etc.). This talk describes some surprising nonlinear electrokinetic phenomena in “leaky membranes” whose conductivity and/or charge responds to large applied currents: (i) A leaky membrane can sustain over-limiting current (faster than diffusion) by “current induced membrane discharge”, as salt depletion promotes pH gradients that deionize the membrane; (ii) a fixed-charge leaky membrane can sustain over-limiting current by surface conduction or electro-osmotic convection; and (iii) a leaky membrane can support conductivity shock waves. These predictions are tested experimentally and applied to water purification by ``shock electrodialysis”.