Statically Very Hydrophilic but Dynamically Hydrophobic Surfaces Showing Surprising Water Sliding Performance

Abstract

AbstractIt is generally believed that water droplets on (super)hydrophilic surfaces is spread and strongly pin to the surface. The surface chemistry that achieves the paradoxical surface properties of being statically very hydrophilic, but exhibiting outstanding water sliding properties, has not yet established. Here, a facile approach to prepare such unusual surfaces based on a combination of a sol–gel process using an organosilane containing polyethylene glycol units and tetraethoxysilane, and subsequent alkali‐treatment is reported. The resulting sol–gel thin films are smooth, transparent, hydrophilic (static contact angle (CA) (θS) of ≈37°) and show a liquid‐like nature with both low CA hysteresis (≈4°) and sliding angle (α) for 10 µL water droplets (≈10°). Surprisingly, after alkali‐treatment for sufficient time, the surface becomes very hydrophilic (θS of ≈14°) while improving its dynamic wetting behaviors (CA hysteresis of ≈3° and α for 10 µL water droplet of ≈4°), such that even a mere 0.5 µL water drop can slide down smoothly without pinning and/or tailing.