ABSTRACT
This chapter undertakes a fundamental research program to investigate the less understood but more significant dilatational properties, such as the dynamic surface/interfacial tension, the dilatational modulus, and the surface dilatational viscosity. The interfacial region contains a large concentration of surfactant molecules such that the viscosity in the region is also large. The adsorption of surfactant at a fluid-fluid interface has long been known to alter equilibrium interfacial properties. Surface dilatational properties are those properties that are necessary to define fully a pure expansion or compression of a fluid surface. The dilatational modulus is a very important measure of dilatational surface stress as it expresses in a certain sense the gradient of dynamic surface tension. It is, of course, the gradient of dynamic surface tension that plays a direct role in the surface stress equations. Identifying the reversible and irreversible contributions to the dynamic surface tension is a difficult and open question.
