Fouling resistant, freestanding zwitterionic polysulfones for osmotically driven membrane processes

Providing sustainable and secure access to potable water is a critical challenge facing this generation. Natural water sources are treated to remove salt, organic matter, and biological organisms. As water demand increases, water sources that require more rigorous pretreatment must be utilized. Polymer membranes are a promising technology for these more rigorous water purification demands, as they selectively transport purified water while rejecting contaminants. Although promising, current membranes face two profound limitations: adhesion and growth of biological films on the membrane, and membrane degradation by chlorine. Both effects reduce membrane performance and increase cost due to the need to clean or replace the membrane. This project will design and test new polymeric membrane materials that retain the performance of commercial membranes, with molecular-level modification of the polymer for increased resistance to fouling by biofilms and decreased degradation by chlorine. <br/><br/>Through an integration of macromolecular and process engineering, this project will investigate how molecular level polymeric design impacts processing, microstructure, and separation performance. Poly(arylene ether sulfone) precursors will be modified using post-polymerization modifications to introduce sulfobetaine zwitterions and a series of crosslinkers. The charge and crosslink densities will be optimized to balance hydrophilicity and water sorption versus swelling that leads to a loss of mechanical stability. Then, (anti)fouling mechanisms for the new membranes will be probed, including the role of surface roughness, hydrophilicity, and charge content on protein adhesion. Also, the influence of systematic changes in charge content on physical membrane characteristics will be studied, including water permeability, salt rejection at various salt concentrations and pressure drops, membrane porosity, free volume, morphology, and separation/process costs. Finally, the charge content and processing conditions will be correlated to membrane longevity, specifically structural integrity at various transmembrane pressure drops for asymmetric membranes, resistance to chlorine-mediated oxidative degradation, and long-term fouling studies. One graduate student will be trained in this project and undergraduate students will be involved in the laboratory work. An educational outreach plan is included that will engage the diverse student body of Arizona State University and the surrounding metropolitan community.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.