(387a) Fundamental Salt Sorption and Permeability Properties of Polymeric Membrane Materials

The salt transport properties of polymeric membrane materials are significant for a variety of desalination-related applications.  These applications include several commercialized technologies such as reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), and reverse electrodialysis (RED).  Fundamental structure-property studies on ion transport in hydrated polymers are needed in order to properly optimize materials for salt transport property-critical applications.

Highly-charged polymers, such as sulfonated polymers, exhibit salt permeability properties that are fundamentally different from those properties observed for non-charged polymers, such as poly(ethylene glycol) (PEG).  The sodium chloride permeability of highly-charged polymers increases with increasing upstream sodium chloride concentration in the range of 0.01 – 1.0 mol/L; the salt permeability of non-charged polymers, in contrast, is often negligibly influenced by upstream salt concentration over the same range.  This different behavior results from the presence of covalently bound fixed charge groups, such as sulfonate moieties, in highly-charged polymers.

To further understand fundamental structure-property relationships, we have studied salt permeability and ion sorption in non-charged PEG hydrogels, sulfonated poly(arylene ether sulfone) random copolymers, and sulfonated styrenic pentablock copolymers.  Using the solution-diffusion model, salt permeability and sorption measurements can be used to calculate effective salt diffusion coefficients.  This approach allows us to understand how sorption and diffusion contribute to the upstream salt concentration dependence of salt permeability in highly-charged polymers.  Sodium chloride permeability, diffusion coefficients, and sorption data will be discussed for each of the three polymers considered.  In addition, the differences between non- and highly-charged polymers will be discussed.