Chapter 3 - Surface interaction potentials

Abstract

This chapter discusses aspects that have a direct bearing on particle aggregation and deposition processes, and where some degree of control may be achieved. It focuses on interaction of spherical particles with similar and dissimilar particles and macroscopic surfaces. The fact that an attractive force always exists among colloidal particles of the same material has long been recognized, but a detailed understanding of these forces took a long time to emerge. This attraction between two closely separated surfaces is generally called the London-van der Waals force. The force arises from spontaneous electrical and magnetic polarizations, giving a fluctuating electromagnetic field within the media and in the gap between them. There are two theoretical approaches to the evaluation of London-van der Waals attraction. In the classical (or microscopic) approach, because of Hamaker, the interaction between two macroscopic bodies is obtained by the pairwise summation of all the relevant intermolecular interactions. All expressions obtained in this manner may be split into a purely geometrical part and a constant “A,” the Hamaker constant, which is related only to the properties of the interacting macroscopic bodies and the medium. Typically, “A” lies between 10-21J and 10-19J. Hamaker's method can be easily applied to different geometries. However, the assumption of complete additivity is a rather serious deficiency and the resulting expressions always overestimate the interaction. The additivity assumption is overcome through use of an alternative (macroscopic) approach suggested by Liftshitz in which the interaction is derived entirely from considerations of the macroscopic electromagnetic properties of the medium.