Van der Waals Interactions in Thin Films

This chapter reviews the existing theories of Van der Waals interactions between macroscopic bodies. An essential advantage of the microscopic approach is its simplicity, which is realized by means of the assumption of additivity of pair interactions. A large portion of the chapter deals with examination of different procedures for the determination, from spectral data, of the quantities required for the calculation of Van der Waals energies or forces of interaction, such as dielectric permeabilities or molecular polarizabilities. Common to all these terms is that the average energy and free energy of interaction are negative, i.e., attractive, and vary with the inverse sixth power of intermolecular distance. The extension of Lifshitz theory to the derivation of expressions for forces or free energies of interaction between bodies in other geometries seemed a formidable task. A knowledge of these quantities or functions thereof is required for the calculation of intermolecular forces.