Surface tension coefficient
The surface tension coefficient σ is the partial derivative of the Gibbs free energy G with respect to the area S under the condition of the temperature T and the pressure p unchanged: the unit of the Gibbs free energy is the energy unit, so the unit of the surface tension coefficient is the energy /area. The force that causes the liquid surface to contract is called surface tension. That is, the force between two adjacent parts of the liquid surface to pull each other within a unit length. If the liquid surface is divided into two parts by a straight line of length L, the mutual pulling force F between the two parts is perpendicular to the straight line L and tangent to the surface.