Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session CT12: Plasma-liquid Interaction I |
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Chair: Tanvir Farouk, University of South Carolina Room: Virtual GEC platform |
Tuesday, October 5, 2021 8:00AM - 8:15AM |
CT12.00001: Plasma-Produced Reactive Species Interactions with Liquid Water Droplets Mackenzie Meyer, Gaurav Nayak, Peter Bruggeman, Mark J Kushner The transport of plasma produced reactive species to liquid droplets in atmospheric pressure plasmas produces chemically active liquids for biotechnology and agriculture. Droplets having large permittivity are electrically dynamic due to their polarization which in turn affects production of ions and radicals in their vicinity. Charging and evaporation of the droplet additionally complicate the interaction with the plasma. In this talk, we discuss activation of a liquid water droplet by an atmospheric pressure He radio frequency glow discharge. To better understand the interactions of short-lived reactive species and the droplet, formate (HCOO-aq) is dissolved in the droplet, and the change in HCOO-aq concentration quantifies the interactions between OHaq and the droplet. These interactions are computationally investigated using the 0D model GlobalKin and the 2D model nonPDPSIM. On a time-averaged basis, the polarization of the droplet maximizes the electron temperature near the poles of the droplet, producing more reactive species at that location. The results of the models will be compared to companion experiments. |
Tuesday, October 5, 2021 8:15AM - 8:30AM |
CT12.00002: Droplet Emission in a 1 atm DC Glow Discharge with Liquid Electrode: Observations and Potential Mechanisms Zimu Yang, Yao E Kovach, John E Foster The thermodynamics and transport processes in a multiphase plasma-liquid interaction can couple with ionized species, chemical reaction, and charge dissipation and thus are complex. The intense mass and heat transfer between the gas and liquid phase provide channels for reactive species in the form of evaporation, gas dissolving, and convection. Interestingly, the injection of liquid droplets in a DC glow discharge using liquid as the electrode is also observed and could be an important coupling mechanism for multiphase plasma. For the liquid cathode, Taylor cone can be formed due to charged surface deformation and give rise to droplets injection into the gas phase. On the other hand, a similar injection phenomenon can also be found with a liquid anode. Such injection starts from the bubble accumulation in liquid phase and subsequent emergence from the anode plate. There appears to be a relationship between the impinging of the bubbles at the interface and the emission of droplets. The electric field in the gas phase can significantly affect these micron-scale droplets' trajectories. Spectroscopic analysis of discharge light emission indicated that droplets that contact the hot cathode electrode emit a glow signature that is similar to that observed in the plasma column. This observation suggests that the strong discharge glow at the interface and in the plasma column might partially originate from the continuous evaporation of these droplets in the hot plasma column, which ultimately introduces electrolyte ions into the gas phase. |
Tuesday, October 5, 2021 8:30AM - 8:45AM |
CT12.00003: Liquid micro-droplet dynamics in an RF-driven glow discharge at atmospheric pressure Gaurav Nayak, Mackenzie Meyer, Mark J Kushner, Peter Bruggeman The charging and stability of liquid droplets in an electric field have been extensively studied in the context of Coulombic fissions and Rayleigh limit/instability, while the dynamics of charged droplets have been investigated in electrosprays. Although these studies employed mostly unipolar charging of droplets, droplets in a plasma experience ambipolar charging involving both electrons and positive ions. In this contribution, we report on the dynamics of water micro-droplets carried by the gas flow through an atmospheric pressure helium RF glow discharge. The operating conditions allow these droplets to pass through the plasma with minimal evaporation and without reaching the Rayleigh limit. The droplet trajectory in the presence and absence of the plasma provides information on the droplet velocities. In doing so, different forces experienced by the droplet are determined. Using the equilibrium of these forces and the droplet charge estimated from a model, the ambipolar electric field at the edges of the plasma can be estimated. These results are compared with the calculated charging of droplets in multiphase plasma-liquid interaction models. |
Tuesday, October 5, 2021 8:45AM - 9:00AM |
CT12.00004: Modeling silver nanoparticle synthesis via pulsed and RF plasma electrolysis Astrid L Raisanen, Stephen Exarhos, Leighton Jones, Chelsea Mueller, Sanjana Kerketta, George C Schatz, Peter Bruggeman, Mark J Kushner In plasma-driven solution electrochemistry (PDSE), charged species and radicals are first produced in a gas phase plasma, subsequently solvate into an interfacing liquid solution, and finally act as initiators for material synthesis. PDSE has the advantage over conventional electrolysis in being able to produce controllable and large fluxes of electrons into the surface of the solution that are then available for reduction processes. One such process is the reduction of silver cations in solution for the formation of nanoparticles. The PDSE of AgNO3 via an atmospheric pressure plasma jet for formation of silver nanoparticles was computationally investigated using the 0-D plasma kinetics model, GlobalKin, and the 2-D multi-fluid hydrodynamics model nonPDPSIM. The fundamental solution reaction mechanism was developed based on ab initio calculations of the formation of cation and neutral silver clusters. Results from the model are compared with experimental measurements. The parameter space was varied to quantify the relative importance of electrical boundary conditions, aqueous solution type (e.g. water vs ionic liquid), and excitation method (pulsed vs RF voltage) on Ag+ reduction. |
Tuesday, October 5, 2021 9:00AM - 9:15AM |
CT12.00005: Importance of solubility on droplet ejection from liquid gallium interacting with inductively coupled helium plasma Yuki Hamana, Naoki Shirai, Koichi Sasaki Understanding the interaction between plasma and liquid is an important issue for various applications of plasmas. We observed the ejection of droplets from liquid gallium interacting with an inductively coupled helium plasma. In this work, we separately controlled the ion flux (1-6 mA/cm2 ), the ion energy (0-300 eV), and the temperature of the liquid gallium (50-300 ℃) to investigate the mechanism of the droplet ejection by the plasma-liquid interaction. The ion flux and the liquid gallium temperature affected the threshold condition at which droplets started to be ejected. On the other hand, the ion energy was not involved in the initiation condition of the droplet ejection at all. We observed the formation of bubbles on the liquid surface. The ejection of droplets was observed at the timing of the collapse of the bubbles, indicating that the mechanism of the droplet ejection is closely related to the dissolvation of helium in the liquid gallium. The bombardment of helium ions, which are accelerated in the sheath electric field, causes the supersaturation in the amount of helium atoms in the liquid gallium. The supersaturation leads the formation of bubbles in the liquid, and the collapse of the bubbles is responsible to the droplet ejection. |
Tuesday, October 5, 2021 9:15AM - 9:45AM |
CT12.00006: Prediction of plasma-induced reactions in a droplet placed in an atmospheric-pressure helium plasma Invited Speaker: Fumiyoshi Tochikubo Plasma-induced liquid-phase reactions initially occur at the plasma-liquid interface. Thus, the use of droplets is advantageous to enhance the plasma-liquid interaction due to their large specific surface area. In a uniform plasma, droplets are charged negatively, and the droplet charging controls the electron and ion fluxes from the plasma, which affects the chemical reactions in the droplet. In this work, we have developed a model to simulate chemical reactions in a droplet in a uniform plasma, taking into account the droplet charging and the associated changes in the potential, electron and ion fluxes. First, the behavior of the droplets in the plasma was experimentally studied using a high-speed camera. The droplets with diameter of approximately 120 μm were dispensed into atmospheric-pressure (AP) He DBD driven by a sinusoidal voltage of 100 kHz. The droplets travelled for several ms in the plasma without visually decreasing their size, and were repelled at the sheath edge, indicating negatively charged. This suggests that the droplet evaporation in He DBD is less effective at least for a few ms due to the low temperature. In the modeling, continuity equations for charged/neutral species in both the gas and liquid were solved with Poisson’s equation, in a limited region around a single droplet placed in AP He glow discharge. Boundary conditions for these equations were taken from one-dimensional discharge simulation. The diameter of the droplet was set to 8 μm. The droplet was salt water or silver nitrate solution. In the DC glow discharge with a plasma density of 1011 cm-3, the droplet charge reached a steady state within 1 us. Similar result was obtained in AP He DBD. Reactions in the droplet were initiated by hydrated electrons or OH at the interface. In the droplet of 10 mM silver nitrate solution, the silver ions were converted to other species by oxidation or reduction within 10 ms. |
Tuesday, October 5, 2021 9:45AM - 10:00AM |
CT12.00007: Pulsed Discharges in Immiscible Layered Liquids: Fundamental Investigation and Application in Nanoparticle Synthesis Ahmad Hamdan, James Diamond, Kyana Mohammadi In-liquid pulsed nanosecond discharges produce highly dynamic plasmas that can be applied in different fields. In this study, we investigate the discharge dynamics of plasmas generated at or near the interface of water (with various electrical conductivities) and liquid heptane. The results indicate that at low conductivity (≤ 100 µS/cm), the discharges are most successful when the anode tip is in water and close to the interface. At these conditions, the plasma shape is filamentary, i.e. streamer-like. Meanwhile, at high conductivity (≥ 500 µS/cm), the highest percentage of successful discharges is observed for the case where the anode tip is in heptane, near the interface. The plasma generated at these conditions takes the shape of one wide and intense filament, i.e. spark-like. The transition from streamer-to-spark mode is also confirmed by electrical and optical measurements. Modifying water conductivity by adding metal salts and producing repetitive sparks in hepatne were found efficient to produce composite nanomaterial. This latter contains nanoparticles, that are produced via ions reduction by the plasma, and carbon matrix, that is produced via the disccociation of hepatne. |
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