Surface energy

Surface energy, or interface energy, quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids, surfaces must be intrinsically less energetically favorable than the bulk of a material (the molecules on the surface have more energy compared with the molecules in the bulk of the material), otherwise there would be a driving force for surfaces to be created, removing the bulk of the material (see sublimation). The surface energy may therefore be defined as the excess energy at the surface of a material compared to the bulk.

For a liquid, the surface tension (force per unit length) and the surface energy density are identical. Water has a surface energy density of 0.072 J/m² and a surface tension of 0.072 N/m; the units are equivalent. When a solution is formed comprising a mixture of two liquids or dissolved molecules, the surface tension of the primary liquid can deviate from corresponding pure liquid values. This phenomenon can be described by the Gibbs isotherm.