Discharge Characteristics and Bactericidal Effects of a Self-Condensing Water-Electrode Plasma

Abstract

This study proposes a self-condensing water-electrode plasma device in which ambient water vapor is condensed on a cooled needle-tip electrode within a strong electric-field region, forming continuously renewed water droplets, Taylor cones, or water-film interfaces that participate in the discharge process. The effects of ambient humidity, needle-tip temperature, and applied voltage on the self-condensation behavior were investigated. The discharge modes at different applied voltages and discharge gaps, the generation of reactive species, and the inactivation efficacy against Staphylococcus aureus were also analyzed. The results showed that increasing ambient humidity, decreasing the needle-tip temperature, and increasing the applied voltage all promoted water condensation at the needle tip. The electric field shortened the droplet formation time and reduced the droplet detachment size. As the applied voltage increased, the device sequentially underwent water condensation, electrospray, stable Taylor-cone, water-film discharge, and bare-electrode discharge stages, while the boundary voltage of each stage increased with the discharge gap. The ozone concentration remained below the instrument’s limit of detection during discharge with the self-condensing water electrode, whereas hydroxyl-radical generation was significantly enhanced. Compared with a conventional metal electrode, the self-condensing water electrode exhibited greater inactivation of S. aureus at the same applied voltage, with a more pronounced advantage under low-voltage conditions. These findings demonstrate that introducing a self-condensing water interface can regulate the local discharge morphology and reactive-species composition, providing a new strategy for developing low-temperature plasma sterilization technologies with low ozone production and high bactericidal activity.