CPOS Seminar: "Molecular-to-materials scale design and characterization of membrane materials to enable solute selective separations."
Speaker: Jonathan Aubuchon Ouimet, Postdoctoral Researcher, Segalman Group, Department of Chemical Engineering, UC Santa Barbara
Membrane processes enable separations that are critical to modern society (e.g., isolating pharmaceutical products, desalination, etc.). These successes, in conjunction with the continued demand for energy efficient separations, are driving the development of high performing membranes for resource recovery. The development of solute selective membranes will require improved characterization techniques. This talk details two techniques that bridge the molecular-to-material-scale design of membrane materials.
The characterization of novel membranes require laborious experimental campaigns that impede material screening and substantially limit data quality, leading to high uncertainty in regressed performance metrics. To address these shortcomings, we design an automated diafiltration apparatus that systematically and rapidly explores a broad range of feed conditions. Using the transport of KCl through a commercial membrane as an example, we show that diafiltration experiments characterize membrane materials nearly 50 times faster (1 hour) than a traditional campaign of filtration experiments (47 hours). Furthermore, we highlight that the uncertainty of the regressed transport parameters decreases when conductivity probes are used to continuously monitor the retentate and permeate concentrations. Subsequently, we apply diafiltration experiments to probe how changes in the pore wall chemistry affect ion transport.
While informative, diafiltration experiments and other ex-situ techniques do not describe the mechanisms of solute transport, hindering the rational design of next generation membranes. Therefore, we propose the use of spatially and temporally resolved nuclear magnetic resonance (NMR) to directly measure solute concentration gradients in polymeric networks and at solution-polymer interfaces. We validate this methodology using well characterized poly(ethylene glycol diacrylate) (PEGDA) membranes with varying crosslink densities. The spectroscopic technique will offer promising opportunities to understand how differences in polymer chemistry (e.g., such as those identified from diafiltration experiments) affect ion transport.
