ADHESIVE CONTACT DRIVEN BY ELECTROSTATIC FORCES

摘要

The JKR (Johnson-Kendall-Roberts) theory of contact has been used extensively to study the adhesion of particles. An excellent review of this theory and its applications can be found in the article by Shull. The JKR theory as well as its extension by Maugis, are based on the assumption that the interaction forces that cause adhesion are short ranged. For example, the JKR theory assumes that the contact radius is small in comparion with the particle radius which in turn, is assumed to be much larger than the region where the adhesive forces act. Because it is only within the contact region that the stresses are modified, the JKR theory neglects any surface interaction forces that act outside the contact zone. This assumption is equivalent to "small scale yielding" in fracture mechanics. Maugis's theory accounts for the surface forces that act outside the contact zone, but these forces must be confined to a region that is small in comparion to the particle radius. These assumptions are necessary because both theories are based on the Hertz theory of contact, in which local deformation is computed by approximating the elastic sphere as a half space loaded by the contact pressure and surface forces. This assumption clearly breaks down if the forces are long ranged, as is the case of a charged sphere interacting with a conducting substrate. The following question naturally arises: Can the JKR theory be extended to study the adhesion of charged particles? This work is an attempt to address this question.