Thermodynamic Properties of Water−Ethanol Films Formed between Hydrophobic Surfaces. Part I.

Abstract

Based on thermodynamic reasoning we claim that long-ranged, solvophobic surface forces may arise in thin films of associated liquids due to formation of linear aggregates composed of spheroidal, nano-sized molecular clusters. Supposedly, these aggregates can span a narrow gap between two hydrofobic solid surfaces submerged in the film-forming liquid phase, thus giving rise to attraction. Such aggregates are apparantly generated in thin water and water–ethanol films, especially below room temperature and for high mole fractions of water or ethanol, respectively. The surface force recorded for a pure water with film thickness larger than about 20 nm are found to be proportional to the number of bridging cluster aggregates per unit area that cross the mid-plane of a thin film. Moreover, the long-range-ness (decay length) was seen to depend inversely on the work of formation of the elongated middle part of a bridging cluster aggregate. Furthermore, addition of small amounts of ethanol rapidly reduce the surface force generated for pure water films with thickness of a few hundred nm.