Janus polyvinylidene fluoride membranes with controllable asymmetric configurations and opposing surface wettability fabricated via nanocasting for emulsion separation

Janus membrane (JM) with opposite wettability has great potential in separation of oil-in-water (O/W) and water-in-oil (W/O) emulsions. In this work, we have reported a simple, low cost nanocasting/NIPS strategy for preparation of the superhydrophobic and underwater oleophobic surface of JM for the first time. Poly (vinylidene fluoride) (PVDF) and polyethylenimine (PEI) blend membranes were fabricated on PDMS modified non-woven fabric by non-solvent induced phase separation (NIPS) process. Then the as-prepared membranes were further modified with hydrophilic nano-SiO 2 to improve the hydrophilicity of the top surface. Peel off PDMS modified non-woven fabric, parts of PDMS chains were imprinted to the membrane bottom surface with micro-nano three-dimensional microstructures, resulting in superhydrophobic property. The as-prepared JM exhibits an asymmetric wettability with the water contact angle of 35.3° and 151.8° of the opposite surfaces. By changing the orientation of the membrane, oil or water can be filtered respectively. The as-prepared JM shows excellent separation performance for both O/W emulsion and W/O emulsion, the separation efficiency reached 99.72 % and 99.68 %, respectively, as well as good long-term stability. This work is expected to yield a new way to fabricate the superhydrophobic surface of JM.