Experimental investigation of behavior of bullets dynamics and production of RONS in helium APPJs-liquid interaction: The effect of additive gas components

Abstract

The understanding of plasma-liquid interactions is of major importance in biomedicine and to better adjust the biological processes induced on/in the biological target by atmospheric pressure plasma jets (APPJs). In order to investigate the physical mechanism of the interaction, the discharge visualization, electrical characteristics, the behavior of bullets dynamics, and the production of reactive oxygen and nitrogen species (RONS) in gas and liquid phases are diagnosed when different working gas APPJs are impinging on liquid. The experimental results show that a small amount of N2 or O2 added in He working gas would significantly change the morphology of jet plume and affect the current amplitude due to the promotion of penning ionization. For bullet propagation, the shape and velocity of the bullet display a huge difference, and it may be strongly dependent on the electric field formed by surface charges deposited on the liquid surface; by comparing touching and not touching the liquid surface, the APPJs impinging on the water illustrate a higher emission intensity of reactive species, particularly OH intensity that is due to the water vapor evaporating into the plasma; for the aqueous RONS (H2O2, NO3−, and NO2−) produced in liquid, it is found that the more the H2O2 production is generated in He + O2 APPJ the higher the NO3− and NO2− concentrations are obtained in He + N2 APPJ. Additionally, the liquid activated by H e + N2 APPJ shows the strongest acidification efficiency due to the more concentrations of HNO3 and HNO2 formation.