Janus polyvinylidene fluoride membranes fabricated with thermally induced phase separation and spray-coating technique for the separations of both W/O and O/W emulsions

Janus membrane is an emerging separation material due to its unique separation performance. The asymmetric surface wettability on its two surfaces is crucial for a Janus membrane. In this work, robust Janus polyvinylidene fluoride (PVDF) membranes were prepared via thermal induced phase separation (TIPS) accompanied with spray-coating method. The two surfaces of TIPS-prepared PVDF membranes were rapidly deposited with polydopamine/polyethyleneimine (PDA/PEI) and micro-/nano-scale silica particles crosslinking with diphenyldichlorosilane respectively. The spray-coating endows the Janus membranes with superhydrophilicity and superhydrophobicity on its opposite surfaces. The optimized membrane of M-A0.9B0.2 presents an asymmetric surface wettability. Its hydrophilic surface has a water contact angle (WCA) of 11.2°, while the hydrophobic surface has a WCA of 169.9° as well as a sliding angle of <1°. The superhydrophilic surface allows water to quickly pass through the membrane and oil phase is trapped; while oil can penetrate through the membrane and water is rejected by the superhydrophobic surface. The Janus membranes show excellent separation performance with the highest permeation of 2060.5 L m −2  h −1 ·bar −1 accompanied with above 94.0% oil rejection for toluene-in-water emulsion and the highest permeation of 1769.0 L m −2  h −1 ·bar −1 accompanied with above 97.0% water rejection for water-in-toluene emulsion using the opposite surfaces.