Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session MR2: Plasma Interactions with Liquid |
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Room: State C |
Thursday, November 6, 2014 8:00AM - 8:20AM |
MR2.00001: Detection of solvated electrons at a plasma-liquid interface David B. Go, Paul Rumbach, David Bartels, R. Mohan Sankaran We have recently shown that charge can be transferred from a DC microplasma jet into an aqueous solution to promote electrolytic reduction reactions [1,2]. However, the precise nature of these charge transfer reactions remains poorly understood---in particular, it is not known if plasma electrons solvate and solvated electrons are responsible for the reduction of solution species. To address these questions, we have designed and built an optical absorption spectroscopy system to directly detect solvated electrons at a plasma-liquid interface, which only have a lifetime of $\sim$ 1 $\mu$s. Our preliminary results reveal that plasma electrons do indeed solvate, and survive up to depths of approximately 0.5 nm beneath the plasma-liquid interface. Adding electron scavengers such as nitrite and nitrate salts to the solution causes a decrease in optical absorption, indicating a decrease in the average lifetime of the solvated electrons, further confirming their existence. Measuring optical absorption as a function of scavenger concentration, we extrapolate rate constants that agree well with prior radiolysis experiments. These preliminary findings are consistent with the hypothesis that free electrons from atmospheric pressure plasmas solvate in aqueous solutions, and open potential applications of plasmas for solvated electron chemistry. \\[4pt] [1] M. Witzke, P. Rumbach, D. B. Go, and R. M. Sankaran, \textit{J. Phys. D: Appl. Phys}. \textbf{45}, 442001 (2012).\\[0pt] [2] P. Rumbach, M. Witzke, R. M. Sankaran and D. B. Go, \textit{J. Amer. Chem. Soc}. \textbf{135}, 16264-16267 (2013). [Preview Abstract] |
Thursday, November 6, 2014 8:20AM - 8:40AM |
MR2.00002: Comparison of Plasma Activation of Thin Water Layers by Direct and Remote Plasma Sources Invited Speaker: Mark Kushner Plasma activation of liquids is now being investigated for a variety of biomedical applications. The plasma sources used for this activation can be generally classified as direct (the plasma is in contact with the surface of the liquid) or remote (the plasma does not directly touch the liquid). The direct plasma source may be a dielectric barrier discharge (DBD) where the surface of the liquid is a floating electrode or a plasma jet in which the ionization wave forming the plasma plume reaches the liquid. The remote plasma source may be a DBD with electrodes electrically isolated from the liquid or a plasma jet in which the ionization wave in the plume does not reach the liquid. In this paper, a comparison of activation of thin water layers on top of tissue, as might be encountered in wound healing, will be discussed using results from numerical investigations. We used the modeling platform nonPDPSIM to simulate direct plasma activation of thin water layers using DBDs and remote activation using plasma jets using up to hundreds of pulses. The DBDs are sustained in humid air while the plasma jets consist of He/O2 mixtures flowed into humid air. For similar number of pulses and energy deposition, the direct DBD plasma sources produce more acidification and higher production of nitrates/nitrites in the liquid. This is due to the accumulation of NxOy plasma jets, the convective flow removes many of these species prior to their diffusing into the water or reacting to form higher nitrogen oxides. This latter effect is sensitive to the repetition rate which determines whether reactive species formed during prior pulses overlap with newly produced reactive species. in the gas phase. In the plasma jets, the convective flow removes many of these species prior to their diffusing into the water or reacting to form higher nitrogen oxides. This latter effect is sensitive to the repetition rate which determines whether reactive species formed during prior pulses overlap with newly produced reactive species. [Preview Abstract] |
Thursday, November 6, 2014 8:40AM - 9:00AM |
MR2.00003: Interaction of non-equilibrium plasma jets with liquids: chemistry, transport and biological interactions. Invited Speaker: Peter Bruggerman |
Thursday, November 6, 2014 9:00AM - 9:15AM |
MR2.00004: Non-thermal equilibrium plasma-liquid interactions with femtolitre droplets Paul Maguire, Charles Mahony, Andrew Bingham, Jenish Patel, David Rutherford, David McDowell, Davide Mariotti, Euan Bennet, Hugh Potts, Declan Diver Plasma-induced non-equilibrium liquid chemistry is little understood. It depends on a complex interplay of interface and near surface processes, many involving energy-dependent electron-induced reactions and the transport of transient species such as hydrated electrons [1]. Femtolitre liquid droplets, with an ultra-high ratio of surface area to volume, were transported through a low-temperature atmospheric pressure RF microplasma with transit times of 1 -- 10 ms. Under a range of plasma operating conditions, we observe a number of non-equilibrium chemical processes that are dominated by energetic electron bombardment. Gas temperature and plasma parameters (ne $\sim$ 10$^{13}$ cm$^{-3}$, T$_{\mathrm{e}}$ \textless 4eV) were determined while size and droplet velocity profiles were obtained using a microscope coupled to a fast ICCD camera under low light conditions. Laminar mixed-phase droplet flow is achieved and the plasma is seen to significantly deplete only the slower, smaller droplet component due possibly to the interplay between evaporation, Rayleigh instabilities and charge emission [2].\\[4pt] [1] Mariotti et al., Plasma Process. Polym. 2012, 9, 1074--1085.\\[0pt] [2] E Bennet et al., New J. Physics (submitted). [Preview Abstract] |
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