A wetting experiment as a tool to study the physicochemical processes accompanying the contact of hydrophobic and superhydrophobic materials with aqueous media

In most fields of technological application of superhydrophobic materials, such as protection against corrosion, icing, and capillary condensation, or micro fluidics applications, a superhydrophobic surface has to operate in contact with aggressive aqueous media. Therefore, the peculiarities of behaviour of hydrophobic and superhydrophobic surfaces on prolonged contact with water and the mechanisms of possible degradation of superhydrophobicity need to be discussed. In this study, a consideration of the physicochemical processes accompanying the contact of hydrophobic and superhydrophobic materials with water, acid, alkaline and saline aqueous solutions is presented on the basis of experimental data on three-phase equilibrium obtained by the sessile drop method. It is shown that simultaneous analysis of the contact angle and contact diameter of the sessile drop and liquid/vapour surface tension allows one to attribute degradation of the superhydrophobic and hydrophobic state to reversible and irreversible processes such as hydrolysis of hydrophobic molecules, growth of an oxide layer and so on. A method for estimating both the portion of wetted area and the intrinsic wettability state (hydrophobic versus hydrophilic) of texture elements for a heterogeneous wetting regime is proposed and discussed. (C) 2012 Elsevier B.V. All rights reserved.