Surface energy

Surface energy is the excess free energy associated with a material’s surface compared with its interior. It is commonly expressed per unit area and reflects the energetic cost of creating surface.

Surface tension: The force per unit length, or equivalently energy per unit area, associated with a liquid interface. For liquids, surface energy is measured through the closely related phenomenon of surface tension.
Contact angle: The angle at which a liquid–vapor interface meets a solid surface, measured through the liquid. Measured contact angles are a common practical indicator of surface wettability and energy.
Gibbs free energy: A thermodynamic potential that predicts equilibrium at constant temperature and pressure. Surface energy is a contribution to a system’s free energy, especially when its area changes.
Surface stress: The mechanical stress associated with a material’s surface, arising from changes in surface free energy under strain. Surface stress has units of force per length but is not generally identical to surface energy.
Wulff construction: A geometric method for predicting the equilibrium shape of a crystal from its orientation-dependent surface energies. It turns the anisotropy of surface energy into a predicted crystal shape.
Wetting: The ability of a liquid to maintain contact with a solid surface, governed by interfacial energies. Contact angles show how a solid’s surface energy affects whether a liquid spreads or beads.
Work of adhesion: The reversible work required to separate two phases that are in contact, per unit interfacial area. It links surface-energy values to the strength of contact between unlike materials.
Chemical potential: The change in a system’s thermodynamic potential when the amount of a component changes. Curvature-dependent chemical potential explains why high-energy small particles tend to dissolve or shrink.
Fracture energy: The energy required to create a unit area of new crack surface during fracture. It includes dissipation and deformation, so it can greatly exceed the equilibrium surface energy.
Ab initio thermodynamics: A framework combining first-principles calculations with thermodynamics to predict stable material structures under conditions. It estimates how gas pressure and temperature alter which surface termination has the lowest energy.

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