Bulletin of the American Physical Society
70th Annual Gaseous Electronics Conference
Volume 62, Number 10
Monday–Friday, November 6–10, 2017; Pittsburgh, Pennsylvania
Session ET1: Plasmas in Liquids I |
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Chair: David Go, University of Notre Dame Room: Salon D |
Tuesday, November 7, 2017 10:00AM - 10:30AM |
ET1.00001: Solvated electrons and plasma -- liquid chemistry in plasma exposed microdroplets Invited Speaker: Paul Maguire Transport of micron-sized liquid droplets through a low temperature atmospheric pressure RF plasma [1] has demonstrated some remarkable effects. After a short flight time, \textasciitilde 120 us, rapid plasma-induced nanoparticle chemical reactions have been observed, significantly faster than observed in plasma -- bulk liquid studies and many orders of magnitude faster than in standard bulk chemistry. The microdroplet system allows for a controlled gas environment, a large surface area to volume ratio, very small reaction volume, low droplet temperature, in-flight chemical synthesis and encapsulation of nanoparticles, and their remote delivery. Nanoparticles can be formed without surfactant or surface ligands and can be delivered to surfaces, cells or liquid downstream. The in-droplet synthesis rate of nanoparticles was estimated to be at least 7 orders of magnitude faster than standard synthesis processes involving colloidal chemistry. It was also much faster that approaches based on microfluidic microreactors or high energy radiolysis.[2] The droplet chemistry leading to nanoparticle formation is complex. The plasma feed gas contains only noble gases along with H$_{\mathrm{2}}$O from the evaporating droplet. Other observed chemical species in the liquid are H$_{\mathrm{2}}$O$_{\mathrm{2}}$ and OH, most likely due to generation of these species in the plasma phase. The H$_{\mathrm{2}}$O$_{\mathrm{2}}$ concentration reached 30 mM after 120 us plasma exposure. The degradation rate of Methylene Blue dye due to OH radical bombardment was observed with varying distance up to 150 mm from the plasma source. Results from radial diffusion reaction simulations will be presented. [1] PD Maguire et al., Appl. Phys. Lett. 106, 224101 (2015) [2] PD Maguire et al., Nano Lett., 17, 1336--1343 (2017) [Preview Abstract] |
Tuesday, November 7, 2017 10:30AM - 10:45AM |
ET1.00002: A novel wire-to-cylinder plasma-water-setup for environmental applications Katharina Stapelmann, Carolin Ratering A novel plasma-water setup was built for water treatment for environmental applications. The high-voltage electrode is a capillary, allowing different gases to be injected to the liquid. The grounded electrode is a cylindrical mesh, wrapped around a glass cylinder. As a first step, the properties of the influx of the gas are investigated optically and by Schlieren imaging. Further, the discharge behavior is investigated optically by means of CCD camera imaging and optical emission spectroscopy. The discharge behavior is correlated to the gas influx. First colorimetric investigations reveal insights to the production of chemical species, such as nitrate and nitrite. Based on terephthalate dosimetry, production and diffusion of OH radicals is observed by fluorescence measurements. [Preview Abstract] |
Tuesday, November 7, 2017 10:45AM - 11:00AM |
ET1.00003: Studies of discharges in high conductivity liquids using fast imaging and simulations. Leonidas Asimakoulas, Mohammad Karim, Tom Field, Bill Graham Discharges can be produced in high conductivity liquid at low voltages (\textasciitilde 300 V). Here this is achieved within a cathodic, 500 nm radius pin-to-grounded plate electrode environment. The investigation is centered around a Photron SA-X2 fast framing camera operating at between 60-100 kHz framing rates with synchronized current and voltage measurements. The discharges are observed from their light emission with no backlighting. Shadowgraphy shows they are generated in low-density regions formed close to the pin. This fine tip structure allowed confirmation of vapour growth beginning at the highest electric field gradient. The first observable bubble, with 30 um diameter, is formed at the tip within 2 microseconds of the 300 V, 60 ns rise time pulse. More bubbles then coalesce up the electrode and down from the tip. The discharges with us lifetimes are contained within the bubbles and depend on liquid's conductivity and applied voltage. A finite element analysis simulation of the vapour, electrical field and discharge behaviour will be presented. The authors want to gratefully acknowledge Prof Franta Krcma for his assistance. [Preview Abstract] |
Tuesday, November 7, 2017 11:00AM - 11:15AM |
ET1.00004: Investigation of droplet generation induced by atmospheric pressure glow discharge in contact with liquid Naoki Shirai, Goju Suga, Shusuke Nishiyama, Koichi Sasaki Atmospheric pressure non-thermal plasma in and in contact with liquids has been studied for a wide range of applications. Although many researches have been reported about plasma using liquid electrode, the detail mechanism of the plasma-liquid interaction have not been understood completely. For example, optical emission mechanism of metal cation (such as Na$^{+}$) transported from liquid (NaCl aq.) electrode is still unclear. In this study, we focused attention on droplet generation from liquid electrode when liquid electrode discharge is generated. The droplet generation depends on optical emission from the discharge. The droplet dynamics in plasma was observed by laser light scattering. With increasing concentration of NaCl aq., amount of droplet increased and distance of scattered droplet became longer. Namely, amount of droplet depend on the concentration of NaCl aq. solution. When we use the NaCl aq. solution mixed with other electrolyte including metal cation such as CuSO$_{4}$, intensity of spectral emission of Cu increased compared with the case of using only CuSO$_{4}$ aq. solution. These results indicate that droplet generation which depends on concentration of NaCl aq. is important factor for transport of metal cation in solution to gas phase. [Preview Abstract] |
Tuesday, November 7, 2017 11:15AM - 11:30AM |
ET1.00005: DC driven low pressure glow discharge in high water vapor content: A characterization study. Malik Tahiyat, Tanvir Farouk Plasma discharge in liquid medium has been a topic of immense interest. Theoretical efforts have been pursued to get insight on physicochemical processes being influenced due to trace water vapor either present as residual or provided at known concentration. However, studies on discharge at high vapor content is limited. In this study discharge characteristics of plasma in high water concentration (\textgreater 90{\%}) is investigated experimentally for pressure range of 1--15 Torr to maximize vapor loading without condensation. Voltage-current characteristics was obtained over 0-14 mA of current for each operating pressure; current density was determined to ensure normal glow regime of operation. Spatially resolved optical emission spectroscopy was also conducted to determine OH, O, H$_{\mathrm{2}}$ and H distribution in the interelectrode separation. The normalized intensities of OH and O emission lines are found to be more prominent in positive column, whereas the emission lines of H are most intense in cathode glow region. The electric field distribution along the discharge gap was also measured. We envision that data obtained from this characterization study will also provide valuable data for validation of plasma kinetic schemes associated with water vapor. [Preview Abstract] |
Tuesday, November 7, 2017 11:30AM - 11:45AM |
ET1.00006: A Multiphase Computational Model for Non-Equilibrium Plasma Discharge in Gas Bubbles Immersed in Liquid Ashish Sharma, Dmitry Levko, Laxminarayan Raja Plasma generated by electrical discharges in gas bubbles suspended in liquids has found application primarily in liquid fuel reforming and plasma combustion. It is important to resolve the plasma discharge in both gas and liquid phases to accurately capture the physics of this discharge. Hence, in this work, we present a computational model for non-equilibrium plasma discharge in liquid phase and extend the existing computational framework for plasma discharge in gases to include both liquid and gas phases. The computational model is based on the self-consistent, multispecies continuum description of the plasma and solves the governing equations in both liquid and gas phases simultaneously. This new model considers the variations in the conductivity of the liquid dielectric for a more realistic description of the plasma discharge. The model also allows transport of charged and neutral species between gas and liquid phases through the bubble surface, where the transport terms in the liquid phase consists of both drift and diffusion terms. [Preview Abstract] |
Tuesday, November 7, 2017 11:45AM - 12:00PM |
ET1.00007: Kinetic and graph-theoretic approaches to model plasmas in liquids Tomoyuki Murakami, Thomas J Morgan, Lutz Huwel, William G Graham Plasma interaction with gas-liquid interfaces is be-coming increasingly important in biological applications. The numerical and theoretical works to be presented here focus on general plasma initiated chemistry in gas-liquid interfaces. Two different approaches, a kinetic theory and a graph theory are used to model the complex chemistry. To describe the plasma-dynamics in the water vapor layer, a time-dependent 1-D numerical simulation combined with the detailed chemical kinetic model has been developed. Furthermore, the chemical reactions are analyzed using graph theory. Since the chemistry is complicated enough for the formation of web-like networks, we can identify which species play central roles to trigger subsequent reactions. [Preview Abstract] |
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