Revealing the mechanism of superwetting fibrous membranes for separating surfactant-free water-in-oil emulsions

Although massive superwetting fibrous membranes have been developed for separating water-in-oil emulsions, the optimization of their separation performance is still a challenge due to their unclear separation mechanism. Herein, two kinds of superwetting fibrous membranes were designed for separating surfactant-free water-in-oil emulsion and their separation mechanism was thoroughly revealed. Firstly, the underoil superhydrophilic fibrous membrane and the underoil superhydrophobic fibrous membrane were fabricated, then their separation performance was evaluated. Furthermore, the coalescence process of emulsified water droplets on and within the fibrous membrane was directly observed by the dye-tracking experiment and the coalescence dynamics of emulsified droplets were further investigated via the phase-field simulation method. Finally, a model for understanding the separation mechanism of superwetting fibrous membrane for surfactant-free water-in-oil emulsion was proposed. Additionally, the designed fibrous membrane exhibited an ultrafast emulsion permeation flux up to 50,000 L/m(2)h with high separation efficiency of > 99.6% under a negative pressure, demonstrating a great industrial application potential for the treatment of water-in-oil emulsion.