Universal Charged Nanostructured Polymer Membranes for Ion-Selective Separations

Charged polymer membranes are of great interest in various applications for environment, energy, and health. Designing charged polymer membranes with desirable structural and transport properties is required to advance the above technologies, in particular, water purification, critical element extraction and polymer electrolytes in energy storage. In order to establish the design principles of charged polymer membranes for ion-selective separations (e.g., Li separation), we designed universal charged nanostructured polymer membrane systems to develop molecular through macroscopic structure-transport property relationships in these materials. Our starting model polymer is sulfonated polystyrene-b-polyisoprene-b-polystyrene (S-SIS) triblock copolymers with controlled cross-linking density and varied charged group concentration. A series of uniform-thickness, transparent polymer membranes was successfully prepared. We evaluated fundamental physical and structural properties and correlated them with water and ion transport properties in the polymers. Characterization methods include ¹H-NMR, thermal analysis (DSC, TGA), FT-IR analysis, and transport measurements (permeability, solubility and diffusivity) of water and ions. This universal block copolymer system can help to elucidate the mechanism of ion and water transport in the polymer membranes. This understanding is crucial for designing innovative polymer membranes for challenging ion-selective separations, in particular, Li extraction.