1 Wetting of Surfaces and Interfaces: a Conceptual Equilibrium Thermodynamic Approach

Owing to the focus on molecular engineering of intelligent materials, growing in- terest has been focused on the specific interactions occurring at molecular dis- tances from a surface. Advanced experimental techniques have been developed in- cluding instruments able to measure directly interactions at nanometer distances and to identify special structural features with comparable perpendicular and lat- eral resolution. With this new information at hand, the theories of molecular in- teractions have been re-evaluated and developed further to encompass specific in- teractions such as Lewis and Brønsted acidity and basicity. However, the new the- ories are based on critical approximations, making the upscaling to macroscopic condensed systems uncertain. Therefore, the aim of this study was to evaluate some recent models by introducing macroscopic work functions (cohesion, adhe- sion, spreading and immersion) of wetting of solid surfaces within the proper con- ceptual thermodynamic (macroscopic) framework. The properties of binary and ternary systems are discussed with the focus on four non-ideal inorganic (SiO2 and TiO2) model substrates. The results obtained after applying the recent and more traditional models for dispersive and specific (polar) interactions are com- pared with those utilizing simplifying assumptions. The sources of uncertainties are sought, e.g. from the contribution of surface pressure determined from con- tact angle and adsorption isotherms. Finally, the influence of chemical and struc- tural heterogeneities and also external stimuli on wetting is briefly discussed.