Chapter 14 - Electrostatic Forces between Surfaces in Liquids

Abstract

This chapter examines the electrostatic forces between surfaces in liquids. Two similarly charged surfaces usually repel each other electrostatically in solution, though under certain conditions they may attract at small separations. Zwitterionic surfaces, characterized by surface dipoles but with no net charge, also interact electrostatically with each other, though the force is usually attractive. In complex systems, long-range electrostatic forces are involved. This chapter begins with a discussion on the charging of surfaces in liquids. It then explains the charged surfaces in water and the Poisson–Boltzmann equation. The chapter proceeds with a discussion of origin of the ionic distribution, electric field, surface potential, and pressure. Limit of large separations and limit of small separations are explained in detail. A study of electronic double-layer interaction forces and energies between various particle surfaces is then presented. Exact solutions for constant charge and constant potential interactions are then discussed. Concepts of asymmetric surfaces, ion-condensation and ion-correlation forces are reviewed. The DLVO theory for van der Waals and double-layer forces is explained. The chapter concludes with a discussion on experimental measurements of double-layer and DLVO forces.