(463h) Using Inkjet Printing Devices to Fabricate Charge Mosaics from Chemically Tailored Copolymer Membranes

Charge mosaic membranes, which have distinct anionic and cationic domains that traverse the membrane thickness, allow dissolved salts to permeate rapidly. As such, they can be utilized in a variety of applications that require the selective permeation of ionic solutes (e.g., piezodialysis). In this talk, we will introduce our efforts to prepare charge mosaics from copolymer membrane precursors using ink-jet printing devices. The copolymer precursors are chemically tailored so that well-defined counter-charged domains can be introduced on the surface of the membranes. Specifically, a polyacrylonitrile-based copolymer was synthesized via a free radical polymerization mechanism and its chemical composition and molar mass characterized using nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC), respectively. Copolymer substrates, which possessed nanopores with a diameter around 3 nm in size, were fabricated using a non-solvent induced phase separation (NIPS) method. The azide moieties incorporated into the copolymer precursor used to fabricate these membranes represent an attractive platform for the straightforward chemical functionalization of the membrane in the solid state. In particular, copper-catalyzed azide-alkyne click reactions enable rapid one-to-one covalent attachment of positively charged amine moieties or negatively charged carboxylic acid moieties to pore walls of the membrane. The properties of the charge-functionalized membranes were examined using hydraulic permeability, molecular weight cut-off, and streaming potential measurements. Subsequently, an ink-jet printer was used to generate well-defined domains of positive and negative charges within the pores of the copolymer substrate in a systematic manner. Membrane performance was optimized by coordinating the printing conditions with the membrane morphology. Results from Fourier transform infrared (FTIR) spectroscopy analysis demonstrate that up to 95% of the reactive sites can be converted into charged domains using this technique. The printed domains were distinguished and visualized using fluorescent microscopy. A series of piezodialysis experiments were conducted over a range of ionic strength using membranes functionalized with a single charge (i.e., cationic or anionic domains) as well as patterned mosaics of charge (i.e., cationic and anionic domains). Significantly, these experiments demonstrate that charge mosaic membranes are highly permeable to ionic solutes while single charged membranes reject up to 80% of the co-ions present in solution. The versatile and precise control of substrate chemistry at the nanoscale by printers reveal the potential application of resulted mixed mosaic membranes in targeted ion separation.