Thermoresponsive Membranes from Electrospun Mats with Switchable Wettability for Efficient Oil/Water Separations

A simple and versatile method is described to obtain polycaprolactone (PCL) porous membranes, consisting of fibers prepared by electrospinning. The surface of the fibers is modified by grafting poly(N-isopropylacrylamide) (PNIPAM) brushes by surface-initiated atom-transfer radical polymerization (SI-ATRP). PCL mixtures, featuring Br end-functionalized and nonfunctionalized polymer, are used to enable SI-ATRP. Wettability at variable temperatures is governed by the lower critical solution temperature (LCST) of PNIPAM as contact angle and swelling ratio measurements demonstrate. Because of the PNIPAM LCST, the membranes show a variation of pore size with temperature, which is accompanied by flux changes of water permeating the membranes. Temperature gated separation is demonstrated using oil/water emulsions at 1 bar pressure. Typical separation efficiencies are 92% and 25% at 25 and 50 degrees C, respectively. Employment of anionic and neutral surfactants shows that the separation efficiency also depends on the interaction between the membranes and the emulsions.