Capillary effect in Janus electrospun nanofiber membrane for oil/water emulsion separation.

Janus electrospun nanofiber membranes (J-ENMs) have attracted considerable interest as membranes for oil-in-water emulsion separation due to the opposite properties on each side of the membrane. Such properties can provide capillary effect and achieve water unidirectional transportation. However, the capillary effect on performances of the J-ENMs is still obscure. Therefore, it is highly important to investigate the relation of pore size, capillary pressure, and fluid flux of them. For this study, J-ENMs, which have a dual-layer structure with hydrophilic polyacrylonitrile (PAN) and hydrophobic polystyrene (PS) nanofibrous membranes simultaneously, were fabricated via the electrospinning process. Among the fabricated membranes, the large pore sizes of the PS layer of J-ENMs affected capillary pressure leading to a pure water flux increase of nine times that of the small pore size. For emulsion flux, oil droplets can pass through a large pore of the PS layer easily and can cause a decrease in emulsion flux. Nevertheless, the emulsion flux of J-ENMs was 1.7 times higher than that of single layer membrane, which showed a promising application for the oil/water separation field.