Superhydrophobic and breathable SiO2/polyurethane porous membrane for durable water repellent application and oil-water separation

Electrospun polyurethane membrane with porous structure could be used for waterproof and breathable applications, however, due to polar groups in the soft segment of polyurethane, water would easily permeate the membrane. The water repellency of polyurethane membrane could be improved by grafting hydrophobic silica particles onto the membrane to construct rough surface and low energy epidermis. Polyurethane membrane was chemically modified with 4,4′-methylenebis(phenyl isocyanate) to obtain a reactive group, which was then coupled with (3-aminoproyl) triethoxysilane. Thereafter, the treated membrane was added to the preparation solution of hydrophobic silica particles. Herein, the particles constructed the rough surface of the membrane, and hexadecyltrimethoxysilane endowed the membrane with hydrophobic epidermis. The resultant membrane exhibited significant hydrophobicity with high water contact angles (WCA) and low sliding angles (SA) to different aqueous solutions. Under cyclic stretching, the modified membrane displayed durable water repellency (WCA varied between 152.7 and 154.9°, SA fluctuated between 5.0 and 6.5°) and high breathability (8.4 kg·m−2·d−1). Furthermore, the hydrophobic membrane was superoleophilic and had high permeation fluxes for various oils. It could effectively separate (98.5%) the dichloromethane-water mixture over 30 separation cycles.