Calculation of Surface Tension and Contact Angle

Fowler [8] was the first to calculate the surface tension of a simple liquid. The basic idea is to use the intermolecular forces that operate between atoms and molecules. For this purpose it is sufficient to consider the various van der Waals forces Dipole-dipole (Keesom), Dipole-induced-dipole (Debye), and Dispersion (London). 

Dispersion forces are the most important since they occur between all atoms and molecules and they are additive. The London expression for the dispersion interaction u between two molecules separated by a distance r is 

Hamaker [9] calculated the attractive forces between macroscopic bodies using a simple additivity principle. For two-semi infinite flat plates separated by a distance d, the attractive force F is given by 

Fowler [8] used the above intermolecular theory to calculate the energy required to break a column of liquid of unit cross section and remove the two halves to infinite separation. Using statistical thermodynamics he calculated the work of cohesion and found it to be equal to twice the surface tension. 

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