Understanding Polymer Membrane Interactions with Contaminants

Polymer-based membranes are crucial components of separation processes including water purification and clean energy technologies. For water purification applications, polymer membranes can be used to selectively separate salt ions and other contaminants from water and can address individual, agricultural, and industrial water needs around the world. To improve membrane selectivity in light of increasingly contaminated drinking water sources, thermodynamic interactions between polymer membranes and contaminants must be understood. These interactions contribute to permeability (i.e., the ability of the molecule to pass across the membrane) via the sorption component of the solution-diffusion model, which expresses permeability as a product of sorption and diffusion factors. In other words, molecules that favorably interact with the membrane often have higher permeability compared to molecules that experience unfavorable interactions with the membrane. From an engineering perspective, the polymer used to prepare the membrane can be engineered to interact favorably with molecules that should pass through the membrane and unfavorably with molecules that should be rejected by the membrane. These thermodynamic or sorption interactions influence the permeation of different organic molecules (i.e., proxies for organic pollutants) through different membranes. Molecule solubility in the membrane was measured and used to determine sorption coefficients. These measurements were coupled with regular solution theory analysis to learn how polymer chemistry can be modified in response to organic molecule chemistry to optimize membrane selectivity. This research addresses the increasing need to ensure that water-borne organic contaminants do not pose a health risk to drinking water customers as levels of contaminants in drinking water sources continue to increase due to consumer product and industrial process contamination.