ELECTRICAL CHARGES IN NONAQUEOUS MEDIA

From an explosion at Shell's refinery at Pernis to the megahertz oscil lations of an electrically charged micelle in hexane to the most advan ced of electronic imaging processes, electric charges in nonaqueous me dia make their presence known. The study of these electric charges has slowly and steadily increased over the last 50 years or so, but the a nswers to the elementary questions about how charged species are creat ed and how they remain charged are still hotly debated. This review co ncentrates on the low conductivity solutions and dispersions typical o f hydrocarbon media. The model generally accepted for nonaqueous elect rolyte solutions is that the electric charges are stabilized against n eutralization by being held separate in large structures, such as mice lles or complex macroions. Electrical conductivity arises by the field -induced motion of these charged species. The electric-field and conce ntration dependence of the conductivity depend strongly on their size and structure. Particles acquire electrical charges either by preferen tially adsorbing the ion of one sign or the other, possibly still asso ciated with its stabilizing structure, or by an ion dissociating from its surface to be held in some lyophilic structure in the nonaqueous m edium. Many aspects of this model are not universally accepted. The in fluence of water on the creation and stabilization of electrical charg es is reviewed. Water plays a key role in the properties of nonaqueous electrolyte solutions and dispersions but its behavior is complex bec ause it influences both the formation of structures such as micelles, the dissociation of ionic molecules, and reactions on particle surface s. The current theories of the physics of nonaqueous electrolyte solut ions and dispersions are reviewed. This review is presented in the for m of discussions of twenty-two related topics.