Numerical study of atmospheric-pressure argon plasma jet propagating into ambient nitrogen

In this paper, a two-dimensional fluid model is used to study the properties of atmospheric-pressure argon plasma jet propagating into ambient nitrogen driven by a pulsed voltage, emphasizing the influence of gas velocity on the dynamic characteristics of the jet. The simulation results show that the argon jet exhibits a cylindrical shape channel and with the increase of propagation length, the jet channel gradually shrinks. The jet propagation velocity varies with time. Inside the dielectric tube, the plasma jet accelerates propagation and reaches its maximum value near the nozzle. Exiting from the tube, the propagation velocity of the plasma jet quickly decreases and when approaching the metal plane, the decrease of jet velocity slows down. The increase of gas speed leads to the variation of the jet spatial distribution. The electron density presents a solid structure at lower gas flow speeds, whereas an annular structure can be observed under the higher gas flow velocity in the ionization head. The jet length increases with the gas flow velocity. However, when the flow velocity exceeds a critical value, the increased rate of the plasma jet length becomes slow. Additionally, the influence of the gas flow speed on the production and transport of the reactive species is also studied and discussed.

The Influence of a Second Ground Electrode on Hydrogen Peroxide Production from an Argon Plasma Jet and Correlation to Antibacterial Efficacy and Mammalian Cell Cytotoxicity

This study investigates how addition of a second ground electrode in an argon plasma jet influences the production of hydrogen peroxide (H2O2) in deionised water (DIW). Briefly, plasma is ignited by purging argon gas through a quartz tube at 1 litre per minute and applying a sinusoidal voltage of 7 kV (peak-peak) at 23.5 kHz to a high voltage stainless steel needle electrode sealed inside the quartz tube surrounded by single or double copper ring(s) situated downstream of the high voltage electrode that served as the ground electrode(s). The mechanisms of H2O2 production are investigated through the electrical and optical plasma properties and chemical analysis of the treated DIW. We discover that the addition of a second ground electrode results in higher accumulation of charges on the wall of quartz tube of the plasma jet assembly resulting in an increase in the discharge current and dissipated power. This further leads to an increase in the electron temperature that more than doubles the H2O2 production through dissociative recombination of water vapour molecules, whilst still maintaining a biological tissue tolerable gas temperature. The double ground electrode plasma jet is shown to be highly effective at reducing the growth of common wound pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) in both planktonic and biofilm states whilst inducing a low level of cytotoxicity in HaCaT keratinocyte skin-like cells under certain conditions. The information provided in this study is useful in understanding the complex physicochemical processes that influence H2O2 production in plasma jets, which is needed to optimise the development of plasma sources for clinical applications.

Effect of cold plasma on proliferation rate of mammalian cells in vitro

Human keratinocytes HaCaT and human carcinoma cells A431 have been treated in vitro by a cold argon plasma jet with an average power value of 0.72 mW/cm2. There were made estimations of proliferation rate and cell viability in a day after the exposition. In contrast to the cell viability of both cell lines there were revealed significant differences in proliferation rates of keratinocytes and cancer cells after plasma treatment.

Impact of electrical grounding conditions on plasma–liquid interactions using Thomson scattering on a pulsed argon jet

The interaction between an argon plasma jet excited using microsecond duration voltage pulses and a liquid target was examined using Thomson scattering to quantify the temporal evolution of the electron density and temperature. The electrical resistance between a liquid target and the electrical ground was varied from 1 to $$680\, \text {k}\Omega $$ 680 k Ω to mimic different conductivity liquids while the influence of the varying electrical properties on the electron dynamics within the plasma were examined. It was demonstrated that the interaction between the plasma jet and a liquid target grounded via a high resistance resulted in typical dielectric barrier discharge behaviour, with two discharge events per applied voltage pulse. Under such conditions, the electron density and temperature reached a peak of $$1\cdot 10^{15}\, \text {cm}^{-3}$$ 1 · 10 15 cm - 3 and 3.4 eV, respectively; with both rapidly decaying over several hundreds of nanoseconds. For liquid targets grounded via a low resistance, the jet behaviour transitioned to a DC-like discharge, with a single breakdown event being observed and sustained throughout the duration of each applied voltage pulse. Under such conditions, electron densities of $$2{-}3 \cdot 10^{15}\, \text {cm}^{-3}$$ 2 - 3 · 10 15 cm - 3 were detected for several microseconds. The results demonstrate that the electron dynamics in a pulsed argon plasma jet are extremely sensitive to the electrical characteristics of the target, which in the case of water, can evolve during exposure to the plasma.

Plasma-Induced Hemi-Wicking on Sanded Polymer Surfaces

In this paper, a plasma-induced hemi-wicking phenomenon observed on hydrophobic sanded polymer surfaces, polypropylene (PP), polyethylene terephthalate (PET) and polyethylene (PE) is reported. An atmospheric-pressure argon plasma jet was used to treat a limited area of the carefully sanded polymer surfaces to induce the hemi-wicking phenomenon. Such hemi-wicking triggered by the plasma activation is different from the traditional type, which is achieved purely by the surface topography. Surface analyses by X-ray photoelectron spectroscopy (XPS) and water contact analysis (WCA) show that the combination of sanding and plasma treatment increased the oxygen-to-carbon ratio, which is highly beneficial for surface hydrophilicity. The shear stress tests show that the combination of sanding and plasma treatment can enhance the shear stress by 125%, 95%, and 296% on PP, PET, and PE, respectively. The study shows that the newly developed technique by combining the sanding and plasma processing for polymers could be a potentially useful method in future industry applications.