Asymmetric Poly(ionic\nliquid) Porous Membranes by\nNonsolvent-Induced Phase Separation

Polymers with advanced functionalities such as ionicity\nor antifouling\nare actively being searched for ways to improve the performance of\nultrafiltration membranes. This work introduces an asymmetric porous\nmembrane composed of a cationic hydrophobic poly(ionic liquid) (PIL)\nprepared by using the phase inversion method. Relevant parameters\nof the phase inversion process were investigated, such as the PIL\nand poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide\n(PDADMA-TFSI), the use of different nonwoven supports, solvents for\nsolubilization, and prewetting. The optimization of these parameters\nresulted in asymmetric porous membranes with a spongelike porous structure\nand macrovoids. A thin 200 nm PIL asymmetric porous membrane was able\nto reject 44% of bovine serum albumin dissolved in distilled water,\nachieving a final permeate flux of 9.3 L h<sup>–1</sup> m<sup>–2</sup> (18.6 L h<sup>–1</sup> m<sup>–2</sup> bar<sup>–1</sup>) in a dead-end cell operated at 0.5 bar\nand 25 °C. Moreover, the changes in permeate flux using poly(ethylene\noxide) 100 kDa and the change in permeate flux using an acetic acid/sodium\nacetate (AcH/Ac<sup>–</sup>) buffer were studied in comparison\nto the permeate flux measured when filtering water. Strong changes\nin the membrane structure were observed, resulting in high and incremental\npermeate fluxes. However, we were unable to measure the level of protein\nrejection. The recovery of the membrane’s initial characteristics\nafter a series of washes confirmed the stability of the PIL membrane.