Surfactant Surfactant Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. The term "surfactant" is a blend of "surface active agent". In the United States National Library of Medicine's Medical Subject Headings (MeSH) vocabulary, "surfactant" is reserved for the meaning pulmonary surfactant. For the more general meaning, "surface active agent/s" is the heading. Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic
Surface tension area, a certain amount of energy must be added. Gibbs free energy is defined by the equation , where is enthalpy and is entropy. Based upon this and the fact that surface tension is Gibbs free energy per unit area, it is possible to obtain the following expression for entropy per unit area: Kelvin's equation for surfaces arises by rearranging the previous equations. It states that surface enthalpy or surface energy (different from surface free energy) depends both on surface tension and its derivative with temperature at constant pressure by the relationship. Fifteen years after Gibbs, J.D. van der Waals