Special cases

1. Two surfaces in polar medium

If one of the surfaces were apolar, then

.

If the two surfaces were monopolar with same capabilities, then also

If there is a net repulsion. This situation occurs when . On the other hand when are both either smaller than . This situation corresponds to a net attraction.

Fig. 4.2

Note: The energy of adhesion contains information only about the point shown by the circle (Fig. 4.2). It does not reveal anything about the actual shape of the energy curve. From the figure, it is clear that knowledge of this point does not give information whether the shape of the energy curve is like 1 or 2.