Water uptake and permselectivity were measured for five sulfonated poly(ether sulfone) cation exchange membranes with varying degrees of functionalization from 20% to 60%. Experiments were conducted in aqueous salt solutions of LiCl, NaCl, KCl, Li2SO4, Na2SO4 and K2SO4 to isolate the effect of counter-ions and co-ions on membrane permselectivity. Water uptake ranged from 0.13gwater/gpolymer to 0.76gwater/gpolymer depending on the degree of functionalization and salt used, but was not found to describe the permselectivity differences between salts as the counter-ion and co-ion were varied. This lack of correlation between water uptake and permselectivity is counter to expectations for swollen polymers. Counter-ion binding affinity, charge density and dilute solution mobility were identified as factors influencing membrane permselectivity. Specifically, counter-ions with higher binding affinities to the fixed charge group of the polymer showed lower permselectivities due to counter-ion condensation. Co-ion polarizability was identified as the primary factor for co-ion effects on permselectivity, with more polarizable co-ions resulting in lower membrane permselectivities.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry
- Filtration and Separation