Surface Forces and Disjoining Pressure

The presence of adsorbed hquid layers on a solid substrate is a result of the action of some special forces, referred to as surface forces. 

A new class of phenomena has been introduced [1] surface phenomena, which are determined by the special forces acting in thin liquid films or layers in the vicinity of the apparent three-phase contact line. 

It has been established that the range of action of surface forces is usually of the order of 0.1 pm [1]. Note that in the vicinity of the apparent three-phase 

FIGURE 1.7 Measurement of interaction between two thick plates 1 and 2, possibly made of different materials, with a thin layer 3 in between. 

If h is bigger than =10 cm = 0.1 pm, then the interaction force is equal to zero. However, if h lO cm, then an interaction force appears. This foree can depend on the thickness, h, in a very peculiar way. The interaction forces divided by the surface area of the plate has a dimension of pressure and is referred to as the disjoining pressure [1]. Note that this term is a bit misleading, because the mentioned force can be both disjoining (repulsion between surfaces) and conjoining (attraction between surfaces). 

---

In the following, we briefly review the physical phenomena that result in the formation of the above mentioned surface forces and disjoining pressure. 

---