Asymmetric Poly(ionic liquid) Porous Membranes by Nonsolvent-Induced Phase Separation

Polymers with advanced functionalities such as ionicity or antifouling are actively being searched for ways to improve the performance of ultrafiltration membranes. This work introduces an asymmetric porous membrane composed of a cationic hydrophobic poly(ionic liquid) (PIL) prepared by using the phase inversion method. Relevant parameters of the phase inversion process were investigated, such as the PIL and poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMA-TFSI), the use of different nonwoven supports, solvents for solubilization, and prewetting. The optimization of these parameters resulted in asymmetric porous membranes with a spongelike porous structure and macrovoids. A thin 200 nm PIL asymmetric porous membrane was able to reject 44% of bovine serum albumin dissolved in distilled water, achieving a final permeate flux of 9.3 L h–1 m–2 (18.6 L h–1 m–2 bar–1) in a dead-end cell operated at 0.5 bar and 25 °C. Moreover, the changes in permeate flux using poly(ethylene oxide) 100 kDa and the change in permeate flux using an acetic acid/sodium acetate (AcH/Ac–) buffer were studied in comparison to the permeate flux measured when filtering water. Strong changes in the membrane structure were observed, resulting in high and incremental permeate fluxes. However, we were unable to measure the level of protein rejection. The recovery of the membrane's initial characteristics after a series of washes confirmed the stability of the PIL membrane.