(609d) Elucidating the Effects of Pattern Geometry on Ion Transport through Charge Patterned Membranes

Charge mosaic membranes consist of cationic and anionic domains that traverse the membrane thickness. Due to their mosaic structure, these membranes are capable of transporting ionic solutes more rapidly than neutral particles of comparable or smaller sizes. To date, few charge mosaic membranes have been fabricated successfully and as a result, efforts to prepare such a membrane with high permselectivity are lagging. We recently developed an inkjet printing process that enables the ready fabrication of charge mosaic membranes with controlled patterns of varying surface chemistries. This unique capability was utilized to develop a fundamental understanding of the transport phenomena and membrane-solute interactions that result in the novel properties of charge mosaic membranes. In particular, this talk will focus on the effects of charge patterning on membrane throughput.

Parent nanofiltration membranes based on a poly(acrylonitrile-co-[oligo(ethylene glycol) methyl ether methacrylate]-co-[3-azido-2-hydroxypropylmethacrylate]) [P(AN-OEGMA-AHPMA)] copolymer were prepared. These parent membranes possess pore walls lined by reactive azido moieties that made them amenable to post-synthetic modification via a printing device. Charge patterning was accomplished by deposition of alkynyl-terminated reactants on the surface of azido-functionalized parent membranes to form equal areas of cationic and anionic domains through the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction mechanism. By varying the pattern geometry (e.g., stripes, cubes, hexagons) and feature size between 300 µm - 900 µm, a series of charge patterned membranes were generated. Each of the membrane was distinct from others in respect of its interfacial packing density, which was defined as the total length of the border between oppositely charged domains in a unit area. By executing single salt rejection experiments using these charge patterned membranes, we deomonstrated that the chemically patterned membranes were able to facilitate transport of salt more effectively than the single charge-functionalized membranes. Specifically, the rejection values of symmetric salts (e.g., KCl and MgSO₄) decreased monotonically with increasing interfacial packing density. Notably, a value of -90% rejection for potassium chloride was observed when using a patterned membrane with the highest interfacial packing density. This result revealed the role of electrostatic interactions near the interfacial region between the oppositely charged domains in governing the coupled ion transport and will enable further development of charge mosaic membranes that can be deployed in the many established and emerging technologies where the selective transport of ionic solutes is of critical importance.