A smart fabric with reversibly switchable wettability for controllable oil/water separation

Abstract

Developing pH-responsive superhydrophobic materials for on-demand separation of oil and water using simple and scalable methods continues to be a challenge. In this work, we report a pH-responsive polyurethane (pH-PU) synthesized by reacting aminopropyl-terminated polydimethylsiloxane (NH₂-PDMS-NH₂) with N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine (Y12D). The pH-PU, combined with hydrophobic nano-silica, was thermally cured onto the textile surface to form a pH-responsive coating. The resulting coated fabric exhibits superhydrophobicity (159.4 ± 1.0°) and enables rapid wettability switching, driven by the pH-induced protonation and deprotonation of pH-PU. Notably, the coated fabric retains its superhydrophobicity and self-cleaning abilities even in challenging environments, such as mechanical damage, seawater exposure, UV irradiation, and organic solvent corrosion. More importantly, after plasma treatment renders the surface superhydrophilic, the coating can self-heal to a superhydrophobic state upon heating. Additionally, the fabric can switch between oil and water removal modes based on the type of oil-water mixture. The separation performance was evaluated using mixtures of oils and water with varying densities. Driven solely by gravity, the coated fabric demonstrated high separation efficiency and permeability. Even after five cycles, the separation efficiencies of light oil/water and heavy oil/water mixtures reached 97.8 ± 0.3 % and 97.4 ± 0.2 %, respectively, with fluxes of 11,572.90 ± 466.46 and 13,981.53 ± 1346.84 L·m⁻²·h⁻¹. This work presents a fast and economical strategy for developing fluorine-free, self-healing, pH-responsive superhydrophobic coatings.