Surface active agents (surfactants) are molecules or ions with a dual nature. One or more moieties in a surfactant are ‘water-hating’ (hydrophobic) ‘tail’ groups and one or more are ‘water-liking’ (hydrophilic) ‘head’ groups. Surfactants adsorb from aqueous (or other) solution to various interfaces and in sufficiently concentrated solutions simultaneously aggregate into micelles or other structures. The tail(s) are frequently hydrocarbon or fluorocarbon groups and the head(s) can be polar or ionic. Adsorption and aggregation are often driven by removal of tails from water to an air/water or nonpolar oil/water interface, or to the interior of surfactant aggregates. The ability to adsorb and to aggregate in solution makes surfactants invaluable in industry, in nature, and in the home. Here a brief description is given of the classes of surfactant most commonly encountered, and their usefulness is mentioned. Forward reference is made to appropriate chapters where material is covered in more detail.
On the Temperature- and Frequency-dependence of Visco-elasticity of the Highly Concentrated Solutions of Non-ionic Surface Active Agents