Physics and Dynamics of Adhesion

When two solid bodies have been pressed together under applied load, a normal force is generated at the contact surfaces due to repulsive interaction between atoms. The normal force gradually decreases if the solids in contact are separated along the direction normal to the contact surfaces. In many cases, however, the contact holds even if the normal 

Surface energy or surface tension, y, has been an important parameter widely used for characterizing adhesion. It is dehned as half of the work needed to separate two bodies of unit area from contact with each other to an infinite distance, as schematically shown in Fig. 2. If the contact pairs are of the same material, the surface energy is identical to the cohesive energy. 

Several models have been proposed to predict adhesion force—the maximum force required to pull off the surfaces. Among these, the JKR theory is one receiving the greatest attention [2], which says that for an elastic spherical body in contact with a semi-infinite plane, the adhesion force can be estimated by 

The emphasis of this chapter is on the dynamic nature of adhesion and its interrelations to friction, but before discussing the dynamics a brief introduction to the surface forces responsible for creation of adhesion is given in the following. 

The van der Waals forces result from several sources among which the dispersion forces make the most important contribution. The origin of the dispersion forces may be understood as follows A dipole may appear instantaneously on a 

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