The contact angle as analytical tool

Wetting is the process of making contact between a liquid and a solid. The term wetting describes a displacement of a solid-gas (air) interface with a solid-liquid interface, that is, a process in which Gibbs energy decreases in a system consisting of three contacting phases. The term wettability describes the ability of a surface to maintain contact with a liquid. The degree of wetting and wettability is determined by a force balance between adhesive and cohesive molecular forces. Both wetting and de-wetting of liquids on different surfaces play an important role in many natural and technological processes. Typical examples for wetting-dependent processes are printing, cleaning, painting, detergency, and lubrication. Wetting is also known to be a necessary condition for good adhesiveness. Since Gibbs elaborated the fundamentals of the thermodynamic theory of capillarity [1], diligent work has been performed to describe the wetting behavior of heterogeneous systems, thereby determining surface energies of liquid and solid surfaces and, in this manner, predicting their adhesion behavior. Over a period, plenty of literature data have been accumulated, proposing various measurement techniques and different evaluation possibilities including criticism of one or the other computational algorithm or fundamental idea [2-22].