Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session QW3: Plasma-liquid Interaction ILive
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Chair: Amanda Lietz, Sandia National Laboratories |
Wednesday, October 7, 2020 3:00PM - 3:30PM Live |
QW3.00001: Electromechanical coupling at plasma-liquid interfaces Invited Speaker: Mohammad Hasan In recent years, a variety of atmospheric pressure low temperature plasma sources were developed to chemically activate liquids for a range of applications including bacterial disinfection, seed germination, and plant growth enhancement (Trends Food Sci. Technol. 77 (2018) 21). In many of these sources, there is a direct contact between the plasma and the treated liquid at an interface. Such contact introduces electromechanical coupling at the interface, where the electric field induces a flow of the background gas and the treated liquid through the Electrohydrodynamic (EHD) forces and field-induced stresses at the interface (Nat. Phys.~4 (2008) 149) , while the flow of the liquid influences the electric field by changing the curvature of the interface and the deposited surface charge density (Sci. Rep.~8 (2018) 12037). In this work, an experimentally validated two-dimensional computational model describing a pin-plate discharge configuration, operating in air for treating water, is developed to analyze the electromechanical coupling at the plasma-water interface. Preliminary results indicate that increasing the water's conductivity over a certain range decreases the lifetime of the high electric field penetrating the water close to the interface. As a result, the time averaged EHD forces and the water's flow velocity close to the interface are affected. These findings have important implications for chemical species transport and reactions in the interfacial region of the discharge. [Preview Abstract] |
Wednesday, October 7, 2020 3:30PM - 3:45PM Live |
QW3.00002: Change in discharge current of atmospheric-pressure helium glow discharge by photo-excited desolvation of hydrated electrons Yoshinobu Inagaki, Koichi Sasaki Hydrated electrons are generated by plasma-liquid interaction. However, there have been limited reports on the detection of hydrated electrons in liquids interacting with plasmas. The difficulty is caused by the fact that hydrated electrons generated by the plasma irradiation are localized in a narrow region with a thickness of several nanometers below the plasma-liquid interface. To overcome the difficulty, in this work, we developed a new method to detect hydrated electrons in the interfacial region. Hydrated electrons in the interfacial region are converted to free electrons when they are irradiated with laser beam having a photon energy exceeding the desolvation energy. Free electrons produced by the desolvation are ejected into the gas phase. In the experiment, we used an atmospheric-pressure helium glow discharge with a liquid electrode, and measured the temporal variation of the discharge current when the liquid electrode was irradiated with the Nd:YAG laser pulse at a wavelength of 266nm. As a result, we observed the increase in the discharge current at the timing of the pulsed laser irradiation, which may be due to the ejection of free electrons produced by the desolvation of hydrated electrons. [Preview Abstract] |
Wednesday, October 7, 2020 3:45PM - 4:15PM Live |
QW3.00003: Diagnostics of liquid-side phenomena in plasma-liquid interaction Invited Speaker: Koichi Sasaki We believe that the thin region ($<100$ nm) just below the liquid surface is the key in plasma-liquid interaction. In this talk, we introduce our recent challenges to develop diagnostic methods for observing chemically active species in liquids interacting with plasmas. A research target was solvated electrons. We employed the CTTS (Charge Transfer to Solvent) transition of I$^-$ to investigate the reactivity of solvated electrons. This is a kind of pulsed laser photolysis, and solvated electrons are produced by photodetachment of I$^-$. We observed the temporal decay of the solvated electron density by optical absorption spectroscopy. We examined the influence of the plasma irradiation on the reaction frequency of solvated electrons. We have found that solvated electrons have a higher reaction frequency in the region close ($<1$ mm) to the plasma-liquid interface. However, unfortunately, the absorption spectroscopy combined with the CTTS transition was not applicable to the spatially resolved measurement at the interfacial region just below the liquid surface. Now we try the production of photoelectrons for the detection of solvated electrons at the interfacial region. The photoelectrons are produced by the desolvation. We have already detected the increase in the discharge current of an atmospheric-pressure dc glow discharge due to the production of photoelectrons. In addition, if the time is allowed, we will talk about the detection of luminol chemiluminescence and the measurement of the surface tension at the plasma-liquid interface. The luminol chemiluminescence was observed just below the plasma-liquid interface, and it may be useful for the detection of short-lived species such as OH. We have observed the enhancement of the surface tension of water by the irradiation of a plasma. The enhanced surface tension may be caused by the specialized chemical composition at the interfacial region just below the liquid surface. [Preview Abstract] |
Wednesday, October 7, 2020 4:15PM - 4:30PM Live |
QW3.00004: Temporal Development of Self-Organized Patterns at the Plasma-Liquid Interface for a Helium DC pulsed discharge Tanubhav Kumar Srivastava, Marien Simeni Simeni, Peter Bruggeman Self-organization at the plasma-liquid anode interface is a commonly observed phenomenon for atmospheric pressure plasmas, resulting in patterns with distinctive shapes such as circular rings, star shaped and rotating gear-like structures, depending primarily on the current and solution conductivity. A recent study shows pattern formation can be predicted by Turing stability analysis of the electron and ion reaction diffusion processes in the anode sheath. In the present study, we report on the temporal development of self-organized patterns at the anode plasma-liquid interface for different anode solution conductivities. The model outcome was consistent with the experimentally determined conductivity threshold for pattern formation to occur. While the trend observed in the calculated time constants of instability formation was consistent with experimental observations, the model values were orders of magnitude faster than experimental observations, indicating effects much slower but not considered in the model might impact pattern formation. [Preview Abstract] |
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