(227f) Salt Transport Structure/Property Relationships and Modeling in Polymer Membranes for Water Purification and Power Generation

Providing sustainable supplies of water and energy is a critical global challenge.  Polymer membranes dominate desalination and could be crucial to power generation applications.  These desalination and power generation applications include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED).  Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies.  Water and salt transport structure/property relationships must be used to provide the fundamental framework for optimizing polymer materials for water and salt transport property-critical applications. 

Sodium chloride permeability, sorption, and diffusion properties of poly(ethylene glycol) (PEG) hydrogels, sulfonated poly(arylene ether sulfone) random copolymers, and sulfonated styrenic pentablock copolymers were studied to probe the influence of polymer charge, water content, polymer structure, and micro- as well as nano-scale structural heterogeneity on salt transport properties.  Salt permeability, sorption, and diffusion properties are sensitive to the uncharged or charged (e.g., sulfonated) nature of the polymer.  While salt permeability is generally sensitive to water content, charged polymers exhibit salt permeability properties that are fundamentally different from those properties observed for uncharged polymers, such as PEG.  The sodium chloride permeability of charged polymers increases with increasing upstream sodium chloride concentration in the range of 0.01 – 1.0 mol/L; the salt permeability of uncharged polymers, in contrast, often decreases as salt concentration increases due to decreased water content and free volume as a result of osmotic de-swelling.  The salt permeability behavior observed for charged polymers is a result of covalently bound fixed charge groups, such as sulfonate groups, that affect the salt sorption and diffusion properties of charged polymers.  Salt sorption can be modeled using a combination of Donnan exclusion theory and salt partitioning to further describe the influence of fixed charge concentration, water content, and micro- as well as nano-scale polymer structure heterogeneity on salt sorption and transport properties.