[Terminology] Surface tension, surface free energy and interface tension, interface free energy
Surface tension
Definition 1: the contraction force acting at unit length, being perpendicular and tangential to the liquid surface. Physical unit: mN/m.
Definition 2: the work required to increase the area of a surface isothermally and reversibly by unit amount. Physical unit: mJ/m2.
Definition 1 is derived from mechanics.
Definition 2 is derived from thermodynamics.
Obviously, surface tension that “definition 1” express and surface tension that “definition 2” express have different physical meaning, however, have same dimension.
Typically, interface that surface tension act is liquid-gas interface.
Surface free energy
Definition: the work required to increase the area of a surface isothermally and reversibly by unit amount. Physical unit: mJ/m2. Also known as specific surface free energy.
Obviously, surface free energy is equivalent to “definition 2” of surface tension.
Interface tension
Definition: the contraction force acting at unit length, being perpendicular and tangential to the interface. Physical unit: mN/m.
Typically, interface that interface tension act is liquid-liquid interface, especially is oil-water interface.
Interface free energy
Definition: the work required to increase the area of a interface isothermally and reversibly by unit amount. Physical unit: mJ/m2.