Physical Properties: Surface Tension and Capillarity

The most important effect of surface (interfacial) tension is that a significant pressure, termed capillary pressure, can be generated if the liquid surface is curved. The surface tension of pure liquids is most often modified by the addition of surfactants (surface active agents). Surface tension reveals fascinating aspects of the physics and physical chemistry of liquids (and solids) with major implications for natural phenomena and industrial processes. Together with capillary pressure and contact angle, it forms the subject designated as capillarity. There are two broad approaches in physics: macroscopic and microscopic. The thermodynamic description of surface tension is based on the Gibbs model of the interface. Surfactants are usually classified into anionic, cationic and nonionic. The chapter presents the most common methods for surface tension measurement: pendant drop method, sessile drop and captive bubble method, Wilhelmy plate method, ring method, drop weight method, spinning drop technique, maximum bubble pressure method. Keywords: capillarity; capillary pressure; Gibbs model; microscopic approach; physical chemistry; surface tension; surfactants