Hydrophilicity–Hydrophobicity Characteristics of Solid Surfaces and the State of Water near Surfaces of a Various Nature

Abstract

Values for the surface tension, π, of 85 mJ/m² and for the contact angle of wetting by water as its saturated vapour, θ_V, of 75° are proposed as criteria for distinguishing between hydrophilic and hydrophobic solid surfaces. It is shown that the water boundary layers at hydrophilic surfaces are more ordered while those at hydrophobic surfaces are less ordered relative to the situation in the bulk water structure. The localised model can be used to describe the state of motion of water molecules at a hydrophilic surface, while the motion of water molecules near a hydrophobic surface conforms to the non-localised model.