A series of oil/water separation membranes with tunable surface wettability based on poly­(ionic liquid)­s (PILs) were prepared via a facile one-step photopolymerization of N-vinylimidazolium ionic liquids and divinylbenzene on meshes. The wettability of PIL-based membranes (PILMs) was adjusted by the structures of PILs, specifically the alkyl chain length of imidazolium (butyl and octyl) and anion species (acrylic anion, Br–, and PF6 –). Tunability of wettability resulted in the hydrophilic or hydrophobic property of PILMs. The hydrophilic poly­(1-vinyl-3-butylimidazolium acrylate)-based membrane (PILM-1) transported water and intercepted oil, while the hydrophobic poly­(1-vinyl-3-octylimidazolium hexafluorophosphate)-based membrane (PILM-5) removed oil and rejected water. The two membranes with opposite wettability showed excellent oil/water separation efficiency (above 99%) in batch processes. Continuous oil/water separation was also achieved by assembling PILM-1 and PILM-5 on the fabricated devices. A T-type device could separate various oil/water mixtures continuously, and a tank-type device could separate dispersed oil/water mixtures, with a handling capacity of 46 L within 12 h.

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In this work, poly(ionic liquid)s (PILs) with swelling ability were prepared via the free radical copolymerization of N‐vinyl imidazolium ionic liquids and divinylbenzene. Nuclear magnetic resonance and Fourier‐transform infrared analyses confirmed the successful synthesis of PILs. The PILs were evaluated as demulsifiers for a model oil‐in‐water emulsion, where sodium dodecyl sulfate (SDS) was used as a surfactant. The demulsification efficiencies of PILs increased from 18%, 34%, 92% to 99% with the alkyl chain of three‐substituents on imidazolium varied from n‐octyl, n‐hex1yl, n‐butyl to n‐ethyl, which positively related with the swelling ratios of PILs in the emulsion. The amounts of dodecyl sulfate and Br− in the aqueous phase after demulsification were analyzed by high‐pressure liquid chromatography and ion chromatography, respectively. The decreased amount of dodecyl sulfate coincided with the increased amount of Br−, indicating that the anion exchange between surfactant SDS and PILs was occurred. The PILs could be recycled by ion exchange with NaBr solution and the demulsification efficiencies did not show significant decline during five times of recycling. Meanwhile, P[VEIm]Br@4 Å zeolite prepared by loading poly(1‐vinyl‐3‐ethylimidazolium bromide) on 4 Å zeolite was used for continuous demulsification in the T type device. The T type device had stable fluxes (1083 L ·m−2 h−1) for various oil‐in‐water emulsions with excellent demulsification efficiencies (above 99%).