Ionic Strength of Zwitterionic Polymer Membranes.
- Amphiphilic zwitterionic copolymer membranes exhibit high flux, sharp selectivity and high surface hydrophilicity and have potential uses in various industrial separation processes. However, zwitterions can respond to changes in ionic strength and undergo conformation changes due to anti-polyelectrolyte effect in aqueous environments. In this study, we investigate whether varying ionic strength ... read moreconditions can affect the material properties of these amphiphilic zwitterionic copolymer, therefore changing membrane performance in different feed ionic strength. We found that these membranes are stable in water permeance and solute rejection over a wide range of feed ionic strength because the rigid hydrophobic domains of the copolymer restrict the zwitterionic copolymer domains to respond to varying ionic strength in solution. We also show that annealing these zwitterionic copolymer membranes in different ionic strength solutions can improve the mobility of hydrophobic domains and allow the zwitterionic domains to rearrange in response to higher ionic strength in solution. This leads to significant increase in membrane permeance but only a slight increase in solute rejection. Hence, membrane annealing in different ionic strength solutions may be used to tune and improve the performance of these zwitterionic polymer membranes for high-throughput industrial separation processes.read less