ABSTRACT
Surface active agents, or surfactants, are substances that preferentially localize or absorb to surfaces or interfaces and reduce surface or interfacial tension, respectively. The interfacial tension between two surfaces results from lower forces of attractive interaction between the two materials (∼adhesion) than within the two materials (∼cohesion), which arise from the differences in the types of molecular interactions in a material. For example, hydrocarbon/oil molecules predominantly bind by hydrophobic interactions whereas water molecules bond by hydrogen bonding and polar/dipole interactions. Thus, in an oil-water system, the waterwater interactions and the oil-oil interactions are stronger than the oil-water interactions. This leads to a thermodynamic propensity of the system to minimize the interfacial area, the extent of which may be expressed in terms of interfacial tension. Surface tension is a special case of interfacial tension, when one of the materials is air.
