(222b) Water and Ion Transport in Polymer Membranes for Water Purification

Polymer membranes are critically important in addressing urgent global needs in the 21^st century for reliable, sustainable, efficient access to clean energy and clean water.  Polymer membranes have emerged as a leading technology to desalination water (reverse osmosis and nanofiltration) and are being explored for energy generation in applications such as reverse electrodialysis and pressure retarded osmosis.  Furthermore, efforts are under way to develop additional applications of membranes for water purification, such as forward osmosis and membrane-assisted capacitive deionization.  In each of these applications, control of water and ion transport across polymer membranes is critically important for optimizing performance of such membranes.  This presentation focuses on the fundamentals of ion and water transport in polymers.  Structure/property correlations are shown for a variety of polymers, including uncharged and charged materials.  The solution/diffusion model is described for water and ion transport.  The role of free volume in governing diffusion of solutes through hydrated polymers is demonstrated.  The existence of a water/salt permeability/selectivity tradeoff relation is shown for polymers being considered for such applications.  Comparisons are made to similar physics governing gas transport in polymers used for gas separations applications.