Highly Selective Ionophore-Based Bilayer Emulsion Membranes

Biological channels have been seen as ideal membrane components due to their high throughput and ion-ion selectivity, but their promise is often not realized in engineered biomimetic membranes. However, one recently-developed class of materials that has shown promise in this area is jammed interconnected bilayer emulsions (JIBEs), which are comprised of aqueous droplets joined together by amphiphilic bilayers that contain channels. Here, we investigate the use of ionophores in JIBEs as alternatives to biological channels and develop a crosslinked analog of this material with enhanced mechanical stability. Unlike biological channels, which provide a continuous pathway for ion transport through amphiphilic bilayers, ionophores partition into the bilayers and shuttle ions across them via facilitated transport. Various ionophores were studied to demonstrate the tunability of ionophore-containing JIBEs towards different separations. Most interestingly, JIBEs containing nonactin, an ammonium-selective ionophore, had an NH4+/Na+ selectivity up to 133, and JIBEs containing lithium ionophore VIII had an Li+/Na+ selectivity up to 180. Additionally, a crosslinked interconnected bilayer emulsion (crosslinked IBE) membrane with enhanced mechanical stability was synthesized by photopolymerizing monomers in both phases of an emulsion. Microscopy and capacitance measurements verified that networks of water droplets and the amphiphilic bilayers between these droplets were preserved after crosslinking. Furthermore, crosslinked IBE membranes containing nonactin exhibited an NH4+/Na+ selectivity of 54, which is similar in magnitude to what was observed in JIBEs. Overall, this work demonstrates the implementation of ionophores into biomimetic membranes to achieve highly-selective ion-ion separations and improves the scalability of JIBE membrane platform.