State and structure of water in vicinity of hydrophobic surfaces

摘要

Criterial values of the specific heat of water wetting, surface pressure, and contact angle classifying surfaces into hydrophilic and hydrophobic are proposed based on the analysis of own and published data. The most characteristic properties of hydrophobic surfaces, i.e., large surface area per water molecule in the conventional adsorption monolayer and the absence of continuous two-layer water film on the adsorbent surface at vapor pressure close to saturation, are discussed using nonporous carbonbased materials as example. The presence of residual hydrophilic groups that act as sites of the clusterization of polar molecules on the surface of graphitized carbon black is confirmed by gas chromatography and the concentration of these sites is calculated. The amount of water molecules in the surface cluster is determined at different stages of adsorption. Procedures for preparing organically modified layered silicates and silica as basic objects of the study of the interaction between water molecules and hydrophobic surfaces are considered. It is proven that the boundary water layer in the vicinity of hydrophobic surface consists of a thin (～0.5 nm) depletion layer with a density of 0.4 g/cm~3 and a considerable amount (25-30%) of water molecules with free OH groups and thicker (～35 nm) layer, which is characterized by a more ordered network of hydrogen bonds compared to liquid water. Data obtained by X-ray scattering and neutron and reflection methods, and sum-frequency vibrational spectroscopy are compared with the results of calorimetric study of the interaction between water and hydrophobic surface, as well as with the data of molecular-statistical calculations of the state of water molecules in the surface layer.