ELECTRICAL CHARGES IN NONAQUEOUS MEDIA

From an explosion at Shell's refinery at Pernis to the megahertz oscillations of an electrically charged micelle in hexane to the most advanced of electronic imaging processes, electric charges in nonaqueous media make their presence known. The study of these electric charges has slowly and steadily increased over the last 50 years or so, but the answers to the elementary questions about how charged species are created and how they remain charged are still hotly debated. This review concentrates on the low conductivity solutions and dispersions typical of hydrocarbon media. The model generally accepted for nonaqueous electrolyte solutions is that the electric charges are stabilized against neutralization by being held separate in large structures, such as micelles or complex macroions. Electrical conductivity arises by the field-induced motion of these charged species. The electric-field and concentration dependence of the conductivity depend strongly on their size and structure. Particles acquire electrical charges either by preferentially adsorbing the ion of one sign or the other, possibly still associated with its stabilizing structure, or by an ion dissociating from its surface to be held in some lyophilic structure in the nonaqueous medium. Many aspects of this model are not universally accepted. The influence of water on the creation and stabilization of electrical charges is reviewed. Water plays a key role in the properties of nonaqueous electrolyte solutions and dispersions but its behavior is complex because it influences both the formation of structures such as micelles, the dissociation of ionic molecules, and reactions on particle surfaces. The current theories of the physics of nonaqueous electrolyte solutions and dispersions are reviewed. This review is presented in the form of discussions of twenty-two related topics.