Components of Surface or Interfacial Tension (Energy)

The surface tension (energy) term can be resolved into as many components as are types of intermolecular interactions,

The superscript denotes “Lipshutz–van der Waals” interaction. This term is always present irrespective of whether there is any chemical interaction or not.
The superscript AB denotes the “Acid-Base” interaction. This has to be taken into account when conjugate polar interactions are present between two molecules.

(A) interaction

In orbitals in molecules, there are random fluctuations in the electron cloud which may create a weak dipole. This dipole induces an opposite dipole in the neighboring electron cloud. This opposite polarity results in a force of attraction between them. This is the origin of interaction. This force is always attractive.

(2.14)

Substituting this value in Eq. (2.11), we get

Note that has units of force per unit length or energy per unit area.
A hydrophilic molecule in water will exhibit negative interfacial tension. If interfacial tension is positive then the surface would decrease its area in order to reduce the total surface energy. On the other hand, if interfacial tension is negative then the surface would increase its area in order to reduce the total surface energy.