Design of Fluoro‐Free Surfaces Super‐Repellent to Low‐Surface‐Tension Liquids

Abstract Super‐liquid‐repellent surfaces feature high liquid contact angles and low sliding angles find key applications in anti‐fouling and self‐cleaning. While repellency for water is easily achieved with hydrocarbon functionalities, repellency for many low‐surface‐tension liquids (down to 30 mN m−1) still requires perfluoroalkyls (a persistent environmental pollutant and bioaccumulation hazard). Here, the scalable room‐temperature synthesis of stochastic nanoparticle surfaces with fluoro‐free moieties is investigated. Silicone (dimethyl and monomethyl) and hydrocarbon surface chemistries are benchmarked against perfluoroalkyls, assessed using model low‐surface‐tension liquids (ethanol–water mixtures). It is discovered that both hydrocarbon‐ and dimethyl‐silicone‐based functionalization can achieve super‐liquid‐repellency down to 40–41 mN m−1 and 32–33 mN m−1, respectively (vs 27–32 mN m−1 for perfluoroalkyls). The dimethyl silicone variant demonstrates superior fluoro‐free liquid repellency likely due to its denser dimethyl molecular configuration. It is shown that perfluoroalkyls are not necessary for many real‐world scenarios requiring super‐liquid‐repellency. Effective super‐repellency of different surface chemistries against different liquids can be adequately predicted using empirically verified phase diagrams. These findings encourage a liquid‐centric design, i.e., tailoring surfaces for target liquid properties. Herein, key guidelines are provided for achieving functional yet sustainably designed super‐liquid‐repellency.