Highly Water‐Rich Robust Coating for Separating Immiscible Liquids Mixtures of Wide Range of Surface Tension Differences

Abstract Developing mechanically robust and chemically tolerant coatings that maintain a high water content remains an extremely challenging task to pursue to date. Here, an optimum reinforcement of a hollow nano‐clay i.e., halloysite in a dual crosslinked and interpenetrating polymeric network is introduced to yield a high (≈95 wt%) water content coating with an ability to improve toughness (9.9 ± 0.6 MJm⁻³ Vs. 0.5 ± 0.03 MJ m⁻³) of a deformable fibrous substrate. The association of covalent and physical crosslinking chemistries provides essential tolerance against exposures to diverse severe chemically complex conditions, including extremes of pH, seawater, river water, and organic solvents. High water content in the prepared hydrogel network endows a robust bio‐inspired underwater nonadhesive superoleophobicity with oil contact angle of 160.7 ± 0.2° and force of oil‐droplet adhesion of 8.7 ± 0.3 µN. This approach provides a liquid selective filtrating membrane with ultrahigh crude oil/water separation efficiency (99.7%), superior intrusion pressure (3.5 ± 0.4 kPa), relatively high separation flux (11,162 Lm⁻² h⁻¹), and the ability to perform even when the surface tension of aqueous phase is brought down to similar of oily phase. Moreover, a mixture of immiscible, non‐aqueous liquids having differences in surface tension below 2.5 mN m⁻¹ is successfully separated.