Characterization of Plasma-Activated Fine Water Droplets Generated by Electrostatic Atomization Device
RYO SHIBUI, Tatsuo Ishijima, Tomoya Tamadate, Yohei Ishigami, Yusuke Kuromiya, Toshiaki Sakai, Hiroshi Suda, Takafumi Seto, Kanazawa University
Abstract Number: 667
Working Group: Nanoparticles and Materials Synthesis
Abstract
Plasma-activated water is employed as an agent for inactivation of pathogens such as bacteria, viruses, and fungi due to its rich content of chemically active species e.g., hydroxyl radicals (OH) produced during plasma-liquid interactions at the liquid surface. The efficacy of these interactions is promoted by employing sprayed microdroplets by enlarging the surface area for plasma exposure, resulting in enrichment of the chemical activated concentration per droplet. In this study, we developed a novel device that produces finer droplets using an electrospray technique. We particularly investigated the influence of background gas conditions (N2/O2 ratio) on the droplet number concentration, droplet size distribution, and the generation rate of 2-hydroxyterephthalic acid (HTA) to estimate production of OH in droplets using a chemical probe method. Furthermore, we analyzed changes in the emission spectrum by spectroscopy of the plasma at the Taylor cone tip. The size distribution measurements revealed that ultra-fine particles are generated with minimal variation across all O2 concentrations, with mode sizes ranging from 11.6 to 17.0 nm. Concurrently, droplet concentration measurements indicated a substantial decrease in concentration from 4.85×105 /cc at 0% O2 to 57.4 /cc at 10% O2, subsequently recovering to 4.63×103 /cc at 21% O2. Beyond 21% O2, no significant changes in droplet concentration were observed. Regarding HTA generation rate, it is increased with O2 percentage from 1.54×10-13 mol/s at 0% to 9.88×10-12 mol/s at 100%. However, OH optical emission was not detected by plasma spectroscopy at all O2 concentrations. Plasma spectroscopy also indicated that the purple emission at the Taylor cone tip results from the transition of N2(C-B), with emission intensity decreasing as O2 percentage increases. O optical emission was not detected at integration time of 1 s, with a slight emission at 10 s.