Micro-water droplets in non-equilibrium atmospheric pressure plasma: Evaporation and OH induced chemistry

Summary form only given. Atmospheric pressure plasma has been considered as a promising technology for water treatment, biological decontamination, medical treatment and many other applications. Since these applications share a common feature where the plasma comes into contact with liquid, there has been a growing requirement for a more detailed knowledge of plasma-liquid interactions
¹
. The plasma-liquid interactions have inherent complexities since various physical and chemical processes take place simultaneously. In addition, most of the research on this topic has been conducted using pulsed or dielectric barrier discharges to obtain non-thermal plasmas
²
, which made the system even more complicated due to their special inhomogeneity and time-varying nature. With the aim to obtain the detailed knowledge of plasma-liquid interactions, we have developed an experimental setup in which single water droplets with a specified diameter go through a continuous diffuse atmospheric pressure plasma. In this setup an atmospheric pressure Helium RF plasma is produced in the 2 mm discharge gap formed between two metallic electrodes. Water droplets having diameters of tens of micrometers are generated by a drop-on-demand dispensing device. This system allows us to control the plasma generating conditions, the size and the composition of the droplet and the frequency of the droplet injection independently, making the detailed analyses more feasible. This contribution will report the temporal changes of the water droplet size in the plasma. The droplets experience the heat flux, the ion and electron currents, and the molecular diffusions when they make contact with the plasma. The chemical features of the water droplet after the plasma exposure will also be discussed.