ABSTRACT
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,
12.1 Introduction .................................................................................................. 255 12.1.1 Wetting and Wettability .................................................................... 255 12.1.2 What Is a Contact Angle? .................................................................256 12.1.3 Static and Dynamic Contact Angles .................................................256 12.1.4 Potential of Contact Angle as a Macroscopic Tool Sensitive to
“Nano-Defects” ................................................................................. 257 12.2 A Guide to Contact Angle Measurement ..................................................... 257
12.2.1 Ideal Surfaces ................................................................................... 258 12.2.2 Smooth, Chemically Heterogeneous Surfaces .................................260 12.2.3 Rough, Chemically Homogeneous Surfaces .................................... 261 12.2.4 Contact Angle Hysteresis .................................................................. 262
12.3 Analytical Capabilities Based on Contact Angle Measurement .................. 263 12.3.1 Contact Angle Measurements ........................................................... 263 12.3.2 Surface Tension of a Solid ................................................................264
12.4 Dynamic Contact Angles of Surfactant Solutions ........................................265 Acknowledgment ................................................................................................... 267 References .............................................................................................................. 267
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].
