20.1 Fluid Effects at Interfaces
20.1.1 Origin of Surface Tension
In all materials a certain amount of intermolecular forces keep the individual molecules together. If this force is not strong enough, the material will not exist as a solid bulk decompose but would into individual molecules. In the volume of the material, these intermolecular forces are balanced in all directions. Depending on the nature of the primary bonds, these forces may be directed and more strongly expressed in one specific direction, as is the case for covalent bonds.
However, on the surface of the material, those forces are not balanced (see Fig. 20.1). The last layer of molecules has no interacting neighbors on top of it, and therefore the ...