Highly efficient separation of water-in-oil emulsion using electrospun helicoidal polymer strips

Rationally designed electrospun membranes are commonly used to efficiently separate water-in-oil emulsions. However, obtaining high separation efficiency without sacrificing separation flux cannot be readily attained. Herein, we propose a strategy for controlling the overall geometry of the electrospun product to simultaneously achieve high water-in-oil emulsion separation flux and efficiency. Polycaprolactone (PCL)/polyvinylpyrrolidone (PVP) strips with multi-scale helicoidal structures were readily prepared by using immersion electrospinning. The multi-scale helicoidal structure of the strip could be precisely regulated by controlling the PCL/PVP weight ratio and the applied voltage. The desired helicoidal structure of the immersion electrospun strip provided preferred membrane porosity and thickness, as well as multifaceted wettability, leading to a high water-in-oil emulsion separation flux of 2350 L/m2h and a high separation efficiency of over 99 %. After 10 cycles, the separation flux of the immersion electrospun membrane was still around 60 % higher than that of the nonrecycled conventional electrospun membrane without sacrificing separation efficiency. Moreover, the mechanisms responsible for the excellent performance of immersion electrospun membranes are discussed in depth. This work offers new insight into the rational preparation of advanced electrospun membranes for oil/water separation applications.