(539d) Harnessing Unsteady State Transport Phenomena to Realize Selective Solute Recovery

The growing demand for solute selective separations necessitates the development of materials and processes capable of separating species of similar charge and size. In this regard, there is a growing trend to tune membrane nanostructure to promote single-specie selectivity through membrane-solute interactions. While the interaction strength that facilitates selective transport remains unknown within synthetic membranes, biological proteins inspire a different approach: use an energy source to drive transitions between distinct conformations that modulate interactions with the surrounding environment. Polymeric ion pumps are composite membranes composed of a stimuli responsive gate layer situated on top of a responsive sorbent layer. The gate layer can “open” and “close” to modulate the permeability of solute. The sorbent layer adsorbs solute when the binding sites are active and releases solute when an external stimuli switches the binding sites to their inactive conformation. The two layers are designed to work in concert such that when they are exposed to a time-varying stimulus, a solute flux greater than those that result from steady-state diffusion can be realized.

This presentation examines how the performance and operating conditions of polymeric ion pumps are affected by the permeability of the gate layer. To begin, the transport phenomena within polymeric ions pumps is illustrated. Subsequently, the influence of imperfect gate layers on the performance metrics are evaluated. This information is used to understand how system operating conditions can be changed to promote transport into the receiving solution while minimizing the diffusion of solute back into the feed solution. We then explore whether deficiencies in the gate layer can be overcome by engineering the material properties of the sorbent, or if imperfect gate layers irrevocably hinder the performance of the system. This analysis suggests that current gate layers possess the properties necessary to fabricate polymeric ion pumps.