Polyelectrolyte Complex Tubular Membranes via a Salt Dilution Induced Phase Inversion Process

Abstract

Tubular membrane geometries are key elements of many industrial filtration applications and artificial organs. Established processes to fabricate polymeric membranes require the use of organic solvents, which are prone to be phased out due to stricter regulations. In the quest of developing solvent‐free alternative fabrication processes, polyelectrolyte complex (PEC) membranes are recently discovered, offering a promising alternative. While flat sheet PEC membranes are successfully fabricated, tubular or hollow fiber geometries remain a material engineering challenge. For the first time, the organic solvent‐free fabrication of PEC tubular membranes in a dry‐jet wet spinning process is demonstrated. The aqueous polymer solution comprising the polyanion—poly(sodium‐4‐styrenesulfonate) (PSS), the polycation—poly(diallyldimethylammonium‐chloride) (PDADMAC), and KBr is extruded with the water‐based bore fluid through a single‐orifice spinneret, passing an air‐gap before immersed into an aqueous coagulation bath. The phase inversion kinetics are influenced to form a defect‐free lumen separation layer through the addition of glycerol to the bore fluid. The resulting tubular membranes show reproducible nanofiltration membrane properties. They have a molecular cut‐off of 320 Da, are positively charged and retain salts with a characteristic salt retention hierarchy. This promising material engineering strategy motivates to continue the quest for smaller tubular dimensions toward hollow fibers.

Review of Fiber-Based Three-Dimensional Printing for Applications Ranging from Nanoscale Nanoparticle Alignment to Macroscale Patterning

“…Inkjet-based 3D printing, such as PolyJet, is another method for 3D printing with acceptable resolutions, multimateiral compatibility, and structural complexity that traditional machining or molding cannot achieve. Its unique advantage of incorporating different materials into a single model has shown increasing interest in tooling engineering . Recently, Sochol’s group utilized PolyJet printing to construct a shape-changing spinneret for nanoparticle orientation control .…”

Polyelectrolyte Complex Hollow Fiber Membranes Prepared via Aqueous Phase Separation

“…Recently, Emonds et al fabricated the tubular PEC membranes using PSS and poly(diallyldimethylammonium chloride) (PDADMAC) exploiting salinity as the stimulus for phase separation. 35 Their work provided a significant breakthrough in material engineering toward smaller tubular geometries. However, preparing a stable hollow fiber membrane still remains a significant challenge.…”

Wetting-Induced Polyelectrolyte Pore Bridging

“…The production of thin freestanding, or reinforced polyelectrolyte layers is widely studied in literature [6,13,[22][23][24][25][26]. Reported manufacturing methods involve salt dilution induced phase separation [27,28], sacrificial layers [22,[29][30][31][32][33][34][35], deposition at liquid-liquid interfaces [13,36], deposition at gas-liquid interfaces [23,[37][38][39], and deposition by solvent evaporation [40,41]. Mallwitz et al [42] proposed a method to span PAA/PAH complexes over electron microscopy grids with hole sizes of 100 µm.…”

“…The production of thin freestanding, or reinforced polyelectrolyte layers is widely studied in literature [ 6 , 13 , 22 , 23 , 24 , 25 , 26 ]. Reported manufacturing methods involve salt dilution induced phase separation [ 27 , 28 ], sacrificial layers [ 22 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ], deposition at liquid–liquid interfaces [ 13 , 36 ], deposition at gas–liquid interfaces [ 23 , 37 , 38 , 39 ], and deposition by solvent evaporation [ 40 , 41 ]. Mallwitz et al [ 42 ] proposed a method to span PAA/PAH complexes over electron microscopy grids with hole sizes of 100 m. However, these freestanding structures are not applicable for large scale production for water applications as they are not mechanically stable, the production procedures are complex, or require sophisticated process control.…”