Moldable Strong Cation Exchange Polymer and Microchannel Fabrication

We characterize a high-capacity cation exchange membrane (CEM) synthesized from an aqueous poly­(vinyl alcohol) (PVA) solution and varying amounts of a water-soluble ionic monomer, sodium styrenesulfonate. Highly hydrophilic but water-insoluble transparent polymers with a range of ion exchange capacities (IECs) can be made; at the high end, the ion exchange capacities (IEC) is >2× that of the benchmark CEM, Nafion. The water uptake of the polymer (as moles of water/mole H+) is 5–10× greater than that of Nafion. Except at the highest IECs (where steeply increasing water sorption and resultant swelling outpaces IEC increase), the specific conductance increases with increasing IEC while the conductance anisotropy decreases. The material withstands repeated regeneration cycles and hour-long boiling in water or alcohols. The aqueous prepolymer mixture can be cast around a fine wire acting as a mandrel. Fabrication of an ion exchanger microchannel, capable of withstanding at least 300 psi, is demonstrated. We also discuss entirely novel considerations on ab initio limits of conductance of ion exchange membranes.