Interactions of Non-Equilibrium Plasma with Liquids: Physics, Chemistry and Applications

Abstract

The interactions of non-equilibrium plasmas with a liquid state represent a growing interdisciplinary area of research in the field of plasma science and technology. Plasma-liquid interactions are important in many applications ranging from environmental remediation to material science and health care. Different types of discharge plasmas generated either directly in the liquid, in the gas phase over and in contact with a liquid, or in the multiphase environments such a as discharges in bubbles inside liquids or discharges contacting liquid sprays or foams are used. Much of the work has focused on plasmas in contact with aqueous liquids (primarily water). Depending on the type of discharge, its energy, and the chemical composition of the surrounding environment various types of physical processes (ultraviolet radiation, overpressure shock waves) and plasma-chemical reactions can be initiated. Various short and long-lived chemical species are produced by plasma in the liquid either directly, or transferred from the gas phase discharge plasma being in contact with the liquid. Among these processes, the oxidative properties of reactive oxygen species (OH radical, atomic oxygen, 03, R 2 O2) and nitrogen species (NO, NO2 radical) are generally accepted to play central role in the chemical and biological effects of plasma produced in gas-liquid environments. These species can react at or penetrate through the plasma-gas/liquid interface and dissolve into the bulk liquid, and can also initiate secondary chemical processes in the liquid. In addition to the use for chemical decontamination processes, plasma in liquid can be used for material processing and synthesis (e.g., production of H2 and polymers from liquid hydrocarbons, or production of nanoparticles). There also novel developments in the understanding of electrical breakdown phenomena in liquid produced in nanosecond pulse duration range. In this talk an overview of basic principles of electrical discharge plasmas in liquids will be presented with particular emphasis on elementary physical and chemical processes induced by nonequilibrium plasma in aqueous liquids and their applications.