Physics of Hydrophobic Cavities

Abstract

It has been long believed that modern physics fails in explaining the forces measured between hydrophobic surfaces. We show that the dispersion attraction and cavitation between two uncharged strongly hydrophobic surfaces agree with the classical capillarity and Lifshitz theories. The fluorinated macroscopic glass spheres, with contact angles over 90°, show several times weaker van der Waals attraction across water compared to measurements in air. The aqueous film, stable down to distances shorter than 3 nm, breaks on contact. A bridging vacuum cavity rapidly fills with diffusing air. The long-range capillary force is affected by contact angle hysteresis and pressure regulation effects. The dispersion attraction and cavitation are similar in air-supersaturated and undersaturated water; the stability of the bubbles forming on breaking the meniscus critically depends on the allocation of the system with respect to the coexistence boundary.