Pulsed Atmospheric Pressure Plasma Jet Research Articles

Tomographic optical emission spectroscopy of an atmospheric pressure plasma jet and surface ionization waves on planar and structured surfaces

In this paper, an approach for 3D plasma structure diagnostics using tomographic optical emission spectroscopy (Tomo-OES) of a nanosecond pulsed atmospheric pressure plasma jet (APPJ) is presented. In contrast to the well-known Abel inversion, Tomo-OES does not require cylindrical symmetry to recover 3D distributions of plasma light emission. Instead, many 2D angular projections are measured with intensified cameras and the multiplicative algebraic reconstruction technique is used to recover the 3D distribution of light emission. This approach solves the line-of-sight integration problem inherent to optical diagnostics, allowing recovery of localized OES information within the plasma that can be used to better infer plasma parameters within complex plasma structures. Here, Tomo-OES was applied to investigate an APPJ operated with helium in ambient air and impinging on planar and structured dielectric surfaces. Surface charging caused the guided streamer from the APPJ to transition to a surface ionization wave (SIW) that propagated along the surface. The SIW experienced variable geometrical and electrical material properties as it propagated, leading to 3D configurations that were non-symmetric and spatially complex. Light emission from He, N, and N2 were imaged at ten angular projections and the respective time-resolved 3D emission distributions in the plasma were then reconstructed. The spatial resolution of each tomographic reconstruction was 7.4 µm and the temporal resolution was 5 ns, sufficient to observe the guided streamer and the effects of the structured surface on the SIW. Emission from He showed the core of the jet and emission from N and N2 indicated effects of entrainment of ambient air. Penning ionization of N2 created a ring or outer layer of N that spatially converged to form the ‘plasma bullet’ or spatially diverged across a surface as part of a SIW. The SIW entered trenches of size 150 µm, leading to decreases in plasma light emission in regions above the trenches. The plasma light emission was higher in some regions with trenches, possibly due to effects of field enhancement.

Low‐temperature atmospheric pressure plasma conversion of polydimethylsiloxane and polysilazane precursor layers to oxide thin films

AbstractWe study the conversion of two polymeric silicon precursor compound layers (perhydropolysilazane and polydimethylsiloxane) on a silicon wafer and polyethylene terephthalate substrates to silicon oxide thin films using a pulsed atmospheric pressure plasma jet. Varying the scan velocity and the number of treatments results in various film compositions, as determined by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The mechanism suggested for the conversion process includes the decomposition of the precursor triggered by plasma‐produced species, the oxidation of the surface, and finally, the diffusion of oxygen into the film, while gases produced during the precursor decomposition diffuse out of the film. The latter process is possibly facilitated by local plasma heating of the surface. The precursor conversion appears to depend sensitively on the balance between the different contributions to the conversion mechanism.

Production and diffusion of H2O2 during the interaction of a direct current pulsed atmospheric pressure plasma jet on a hydrogel

The interaction of cold atmospheric pressure plasma jets with hydrogels has been used as a model system to study the interaction of plasmas with tissues. In this study, we analyze the diffusion of reactive oxygen species (in particular H2O2) and quantify the amount of plasma-produced H2O2 species that penetrates into a gelatin hydrogel. We show that the diffusion constant of H2O2 in 10% gelatin hydrogel is similar to its diffusion constant in water and that the production of H2O2 in the hydrogel is significantly less than the production of H2O2 in distilled water for the same plasma operation conditions suggesting that the scavenging of OH radicals at the plasma-gel interface significantly reduces the H2O2 production.

Two competing mechanisms of plasma action on a jet flow

The influence of the plasma generation and propagation in a pulsed atmospheric pressure plasma jet on the gas flow is experimentally studied. The discharge was powered with pulsed voltage signals of both polarities with amplitudes that ranged from 2.8 to 10.8 kV and with the frequencies of 1–5 kHz. It operated in a pure helium and helium with a small admixture of oxygen and nitrogen. The measurements of the flow changes are performed by means of a laboratory constructed manometer with a free membrane. Two plasma action mechanisms have been identified and described: the electrohydrodynamic force mechanism and thermal mechanisms due to the fast localized heating. These two mechanisms appear to be counterbalancing or supporting depending on the experimental conditions. Besides, it was shown that plasma can cause a decrease in the gas velocity, probably depending on the dominant presence of the negative or positive ions in the jet.

Physical interpretation of a pulsed atmospheric pressure plasma jet following parametric study of the UV–to–NIR emission

In the present report, an atmospheric pressure plasma jet is sustained in a helium channel by high square wave unipolar voltage. The gas flow rate and the square wave features (amplitude, frequency, and duty cycle) are varied over a wide range, while the plasma ultraviolet to near infrared emission is recorded. The plasma emission pattern, the propagation dynamics of the involved ionization fronts, the relative density of critical excited species, and the rotational and vibrational temperatures of neutral and ionic species are measured. An optimum operational window is found corresponding to a helium flow rate of 2 slm, a pulse amplitude of 7.5 kV, a pulse repetition rate of 10 kHz, and a pulse duty cycle of 5%–7%. Under these conditions, a plasma jet length close to 45 mm and a gas temperature close to 325 K are obtained, while a high yield of OH, N2(SPS), N2+(FNS), N2(FPS), He*, O*, and NOγ is achieved. The results are found to be in good agreement with the bibliography and motivate a consideration on the involved physical mechanisms. The plasma jet propagation with respect to the reactive species production is discussed based on the local electric field variation over the high voltage pulse width.

Atmospheric-Pressure Plasma Polymerization of Acrylic Acid: Gas-Phase Ion Chemistry

To improve understanding of atmospheric-pressure plasma polymerization processes, the gas-phase ion chemistry of acrylic acid produced in a microsecond pulsed atmospheric pressure plasma jet has been studied using ambient mass spectrometry. Acrylic acid monomer was introduced into the helium feed prior to entry into the active discharge region and the pulse duty cycle was varied from 10–90% for frequencies of 5 and 10 kHz. The ionic mass spectra show a rich variety of species up to 450 Da with prominent peaks at masses corresponding to both positive and negative oligomer ions, [nM+H]+ and [nM-H]−, with up to n = 6 for positive ions and n = 4 for negative ions. Through variation of the pulse voltage parameters, the mass distribution of the oligomer ions produced in the outflow can be manipulated.

Formation of reactive oxygen and nitrogen species by repetitive negatively pulsed helium atmospheric pressure plasma jets propagating into humid air

Atmospheric pressure plasma jets have many beneficial effects in their use in surface treatment and, in particular, plasma medicine. One of these benefits is the controlled production of reactive oxygen and nitrogen species (RONS) in the active discharge through the molecular gases added to the primary noble gas in the input mixture, and through the interaction of reactive species in the plasma effluent with the ambient air. In this computational investigation, a parametric study was performed on the production of RONS in a multiply pulsed atmospheric pressure plasma jet sustained in a He/O2 mixture and flowing into ambient humid air. The consequences of flow rate, O2 fraction, voltage, and repetition rate on reactant densities after a single discharge pulse, after 30 pulses, and after the same total elapsed time were investigated. At the end of the first discharge pulse, voltage has the greatest influence on RONS production. However, the systematic trends for production of RONS depend on repetition rate and flow rate in large part due to the residence time of RONS in the plasma zone. Short residence times result in reactive species produced by the previous pulse still being in the discharge tube or in the path of the ionization wave at the next pulse. The RONS therefore accumulate in the tube and in the near effluent on a pulse-to-pulse basis. This accumulation enables species requiring multiple reactions among the primary RONS species to be produced in greater numbers.

English

The aim of this study was to determine the impact of gamma irradiation and plasma treatment on quality (appearance, odor and texture) and safety (total bacteria count, psychrophilic bacteria, spore forming bacteria, total molds and yeasts) of cold sliced chicken. Pulsed atmospheric-pressure plasma jet (PAPPJ) device is used for the treatment of fresh sliced chicken with different exposure time. Also, another sliced chicken samples were subjected to different gamma irradiation doses. The results illustrate that gamma irradiation and plasma treatment had no real effect on the chemical composition of sliced chicken and the effects of these treatments on the microbial load are reduced the counts of total bacteria, psychrophilic bacteria, total molds and yeasts count. Gamma irradiation and plasma treatment had no effects on the sensory characteristics for appearance, odor and texture of all sliced chicken samples. Finally, gamma irradiation and plasma treatment had no adverse effects on the sensory properties of sliced chicken samples, therefore, their use as safety technological treatments in food preservation and extending shelf-life. Key words: Gamma irradiation, plasma, chicken, microbial load.

Cold plasma is well-tolerated and does not disturb skin barrier or reduce skin moisture

Cold plasma, a new treatment principle in dermatology based on ionic discharge delivering reactive molecular species and UV-light, exhibits strong antimicrobial efficacy in vitro and in vivo. Before implementing plasma as new medical treatment tool, its safety must be proven, as well as assessing skin tolerance and patient acceptance. We investigated the plasma effects of three different plasma sources (pulsed, non-pulsed atmospheric pressure plasma jet (APPJ) and a dielectric barrier discharge (DBD)) on the transepidermal water loss (TEWL) and skin moisture after treating the fingertips of four healthy male volunteers. TEWL values were reduced by pulsed APPJ and DBD by about 20% but increased after non-pulsed APPJ by 5-20%. TEWL values normalized 30 min after all forms of plasma treatment. Skin moisture was increased immediately and 30 min after treatment with pulsed APPJ but was not affected by non-pulsed APPJ and DBD. All plasma treatments were well-tolerated and did not damage the skin barrier nor cause skin dryness. Cold plasma fulfils basic recommendations for safe use on human skin and as future option may serve as the first physical skin antiseptic.

Induction of apoptosis in human breast cancer cells by a pulsed atmospheric pressure plasma jet

By using an atmospheric pressure plasma jet driven by pulsed dc voltage with repetition rate of several tens of kilohertz, we were able to induce apoptosis in cultured human breast cancer cells (MCF-7). The apoptotic changes in cells with plasma treatment were detected by flow cytometry and fluorescence staining assay. A significant portion of these cells was observed to exhibit the apoptotic fragmentation. Helium plasma with additive O2 gas was found to be effective in the induction of apoptosis. This plasma jet provides an effective mode of human breast cancer cell therapy.