G.M. Geise
University of Virginia,
United States
Keywords: polymer membranes, water
Summary:
Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Polymer membrane-based processes dominate the desalination market because they are more energy efficient than thermal desalination processes, and polymer membranes are crucial components in several rapidly developing power generation and energy storage applications that rely on membranes to control rates of water and/or ion transport. Much remains unknown about the influence of polymer structure on intrinsic water and ion transport properties, and these relationships must be developed to design next generation polymer membrane materials. For polymers that are of interest for desalination applications, the water/salt selectivity is a critical property that describes the intrinsic ability of the polymer to transport water as opposed to salt. An observed tradeoff relationship between water/salt permeability selectivity and water permeability suggests that both sorption and diffusion phenomena contribute significantly to water/salt permeability selectivity. To understand the role of polymer backbone rigidity on transport properties, we prepared chemically similar polymers that have different segmental dynamics. At equivalent water content, polymers with slower segmental dynamics are more diffusion selective than those polymers with more rapid segmental dynamics. In many emerging applications, membranes are exposed to ions that are very different from sodium and chloride, which have been used to characterize membranes for decades. Accordingly, ion specific effects have been observed in charged polymers that are of interest for electric field-driven membrane processes, and these effects appear to extend beyond traditional ion exclusion and transport theories. Measured ion sorption and electrochemical permselectivity properties of charged cation exchange membranes suggest that dispersion interactions may contribute to ion specific sorption properties. Additionally, diffusion properties suggest that factors other than ion size influence ion mobility within the polymer. This seminar presents an overview of research aimed at further understanding fundamental structure/property relationships that govern water and ion transport in polymeric materials considered for desalination and electric potential field-driven membrane applications that can help address global needs for clean water and energy.