(638a) Membrane Selective Layers Formed from Amphiphilic Polyampholytes and Amphiphilic Polyelectrolyte Bilayers

Membranes offer a highly energy-efficient, simple to operate, scalable and portable separation method for applications that range from water treatment to oil and gas processing to pharmaceutical manufacturing. Yet, their broader use is typically limited by their limited selectivity and/or fouling in the presence of complex feeds. Current membranes on the market are manufactured from a handful of materials, through well-established processes. However, there is a need for the development of new materials that enable membrane technology to address new separations and perform at a level beyond what current materials can achieve. This presentation will focus on the use of random copolymers that include hydrophobic, anionic, and cationic repeat units in the formation of thin selective layers of thin film composite (TFC) membranes, and how their self-assembly leads to membranes with exceptional and tunable selectivity combined with excellent fouling resistance. First, we will introduce membranes with amphiphilic polyampholyte (APA) selective layers. APAs contain hydrophobic, anionic, and cationic repeat units. The terpolymer is overall insoluble in water, but the self-assembly of the charged groups creates a network of effective “nanochannels” formed of the anionic and cationic groups. Water partially swells these channels, allowing small solutes to pass through. The channel size and the membrane selectivity can be tuned using the anion/cation ratio and the chemical structure of each charged monomer, opening up access to charged nanopores lined with a broad range of available functional groups. Membranes with ~1:1 charge ratios exhibit exceptional fouling resistance, matching the performance of the zwitterionic amphiphilic copolymer membranes we previously developed. More recently, we also prepared membranes by coating thin layers of two different copolymers on a porous support. This “bilayer selective layer” is prepared by first coating a water-insoluble amphiphilic copolymer of a hydrophobic and a charged (anionic or cationic) monomer, followed by the coating of a layer of an amphiphilic copolymer of the opposite charge. Our data indicates that the selectivity of the resultant membrane is distinctly different from each layer alone, exhibiting much smaller effective pore size combined with high permeance. We expect that this arises from the interaction between the two types of amphiphilic polyelectrolytes at the interface of the two layers, resulting in a tighter mesh that controls permeation. Both of these approaches offer an endless range of approaches to develop membranes with controlled functionality that can address many precision separations of need.