Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session WF1: Plasmas and Liquids |
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Chair: Eric Eisenbraun, College of Nanoscale Science and Engineering, the University at Albany-SUNY Room: Saratoga Hilton Ballroom 1 |
Friday, October 23, 2009 8:00AM - 8:15AM |
WF1.00001: Efficient bacterial inactivation in aqueous solution by low-temperature atmospheric pressure plasma application with a reduction of the solution pH Katsuhisa Kitano, Satoshi Ikawa, Atsushi Tani, Naofumi Ohnishi, Satoshi Hamaguchi With some medical applications in mind, bacterial inactivation experiments in aqueous solution have been performed with the use of low-temperature atmospheric pressure plasmas. We have successfully found that efficient bactericidal activity can be achieved if the solution is sufficiently acidic. It is interesting to note that there is a critical pH value of about 4.7 for the bactericidal effects, below which the bacteria are efficiently inactivated and above which the bacteria are hardly affected by the plasma application. When the plasmas were exposed to \textit{E. coli} suspensions at pH 5.2, 4.7, 4.2 and 3.7, D values were found to be 1.92, 0.96, 0.59, and 0.21 min., respectively, under our experimental conditions. It has been also found experimentally that the presence of superoxide anion radicals O$_{2}^{-}$\textbullet in the solution is essential for bacterial inactivation by the plasma application. The critical pH value may be associated with p\textit{K}a of the dissociation equilibrium between O$_{2}^{-}$\textbullet and hydroperoxy radicals HOO\textbullet, which is known to be approximately 4.8. The formation of radicals in solution by such plasma has been confirmed from ESR (Electron Spin Resonance) with spin trapping agents. The ambient gas has been found to influence the radical formation in liquid significantly. [Preview Abstract] |
Friday, October 23, 2009 8:15AM - 8:30AM |
WF1.00002: Properties of Ion Irradiation to Plasma-Ionic Liquid Interface Relating to Metals Nanoparticle Synthesis Takashi Harada, Kazuhiko Baba, Toshiro Kaneko, Rikizo Hatakeyama We investigate basic physics of gas-liquid interfacial discharge plasmas under low gas pressures and effects of ion irradiation to ionic liquids as an electrode on the gold (Au) and platinum (Pt) nanoparticle synthesis by a plasma-reduction method. We successfully measure the Paschen curves using the ionic liquid as a cathode and an anode. We also measure electrostatic potentials in the ionic liquid and the gas phase plasma, and investigate a change of the potential formation which determines the ion irradiation energy $E_{i}$. The Au or Pt nanoparticles can be synthesized using the ionic liquids as a cathode, i.e., ion irradiation on the ionic liquids. It is found that the larger $E_{i}$ enhances the amount of the synthesized Au nanoparticles. In addition, the nanoparticles can be synthesized in a shorter time compared with the case using the ionic liquid as the anode. The Pt nanoparticles are synthesized only by the ion irradiation. Based on these results, it is suggested that the ion irradiation to the ionic liquid is essential to synthesize the metal nanoparticles. [Preview Abstract] |
Friday, October 23, 2009 8:30AM - 8:45AM |
WF1.00003: DC Corona Discharges in Liquids for Thin Film Deposition Bakhtier Farouk, Dion Antao, Alexander Fridman Non-thermal plasma discharges have been extensively studied in gaseous media for various applications in sterilization and materials processing. The study of electrical breakdown in both conducting and dielectric liquids has gained interest due to various applications. Most studies on plasma discharges in liquids were done for applications in switching circuits, capacitors and film deposition. The discharges are unsuitable for many applications due to their thermal nature. Non-thermal discharges in liquids are relatively unexplored. In this study we investigate dc plasma discharges in liquids for a negative pin-to-plate electrode configuration. The discharge is characterized by voltage-current characteristics and visualization. The corona discharge is observed to deposit films on the anode surface when operated in tetraethyl orthosilicate (TEOS). The deposition of films and particles on the anode surface by the proposed method has introduced the possibility of using corona discharges as a novel method of materials deposition or surface modification directly in liquid phase. The proposed PECVD technique is encouraging because it is both simple and effective in depositing films without damaging the substrate material. [Preview Abstract] |
Friday, October 23, 2009 8:45AM - 9:00AM |
WF1.00004: Characterization of DBD Plasma Jet John Foster DBD plasma jet operation underwater was characterized. In this case, the entire discharge operated as a jet submerged underwater. The jet was operated on dry air, nitrogen, argon, and steam. Current-voltage profiles for each gas was obtained. Plasma jet gas temperature dependence on gas type and dissipated discharge power was also characterized. Self-organization of the plasma jet at high argon flow rates was observed. The effect such self organization on observed emission spectra, gas temperature, and water chemistry was investigated using thermocouple, pH, and peroxide measurements. The dependence of gas species type on water chemistry was assessed using an oxidation-reduction dye. [Preview Abstract] |
Friday, October 23, 2009 9:00AM - 9:15AM |
WF1.00005: Effect of polarity and electric field uniformity on streamer propagation inside bubbles immersed in liquids Natalia Babaeva, Mark Kushner Streamers propagating in bubbles immersed in liquids are of interest for the generation of radicals. Streamers often propagate along the surface of a bubble immersed in a liquid instead of propagating along the axis of the bubble. In this talk, we discuss results from a 2-d computational investigation of the propagation of streamers inside bubbles immersed in liquids. We show that dielectric constant and conductivity of the liquid, streamer polarity, degree of electric field non-uniformity and bubble size determine the axial or surface mode of streamer propagation. A bubble of humid air at atmospheric pressure is placed at the tip of corona discharge or near the opposite plane electrode. The bubble is immersed in a liquid of conductivity, $\sigma $, and permittivity, $\varepsilon $/$\varepsilon _{0}$ with radii up to 0.9 mm. For weakly-conducting liquids, the steamer propagates along the axis for low $\varepsilon $/$\varepsilon _{0}$ and along the surface for large $\varepsilon $/$\varepsilon _{0}$. The transition occurs at 4 $< \quad \varepsilon $/$\varepsilon _{0} \quad <$ 8 for positive streamers and at 2 $< \quad \varepsilon $/$\varepsilon _{0} \quad <$ 4 for negative, depending on the size of the bubble and voltage. For large values of $\sigma $ and $\varepsilon $/$\varepsilon _{0, }$the streamer propagates along the surface for both positive and negative polarities. Streamers in bubbles in uniform fields develop from the equator of the bubble where the electric field is enhanced by bubble polarization. [Preview Abstract] |
Friday, October 23, 2009 9:15AM - 9:30AM |
WF1.00006: Plasma parameter variations during liquid droplet injection into low pressure plasmas Daisuke Ogawa, Lawrence Overzet, Matthew Goeckner The direct injection of liquid droplets into low pressure plasmas results in a complex interaction between the evaporating gas, liquid droplets and plasma species. While similar to dusty plasmas, the fact that the droplets are liquid allows their (potentially fast) evaporation in time. This difference can cause wide variations in the reactor state as a function of time after the injection. In this presentation, we show some of those variations and investigate how the liquid evaporation and gas chemistry change affects the plasma parameters. In order to better understand the effects of fast injections at low pressures, we injected argon (gas), nitrogen (gas), hexane (gas), and hexane liquid droplets into the same argon plasma. We will show in-situ measurements of the plasma parameters, (electron density, electron temperature), RF power and optical emission intensity. Specifically, we see that the injection of droplets can very quickly decrease the electron density in the glow even though charging of the droplets could not possibly be the reason and the RF power to the glow is not decreasing commensurately. The injection of gases, even hexane gas, does not result in such a dramatic reduction. [Preview Abstract] |
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