Surface Barrier Discharge Research Articles

Действие продуктов плазмы поверхностного барьерного разряда на прорастание злаков

AbstractSeeds of cereals (spring and winter wheat, winter triticale, and winter rye) were treated with products of surface barrier discharge plasma for various times (30 and 60 min) on exposure outside the zone of active discharge. It is established that the seeds of cereals tested differently responded to this treatment, which is probably related to the degree of their stability under oxidative stress conditions. The response to treatment of the seeds occurring outside the active discharge zone is manifested at greater times of exposure than in the case of direct treatment of seeds by the surface discharge products.

Practical Ozone Disinfection of Soil Via Surface Barrier Discharge to Control Scab Diseases on Radishes

The author has proposed the indirect use of plasma to exterminate soil-borne pathogens and worms as a technique in chemical-free agriculture. So far, laboratory-scale experiments have proven the effectiveness of ozone treatment of soil using a surface barrier discharge to exterminate nematodes. In this paper, an ozone diffusion treatment system was developed and used on an actual agricultural site for soil disinfection. The working depth of ozone in soil was evaluated by measuring the soil acidity and nitrogen nutrients. Then, a section of the field infested with the Streptomyces, which causes scab, was treated with the ozone diffusion system. After the treatment, radish seeds were planted in the ozone-treated area and control area. It was found that radishes grown in the ozone-treated area showed enhanced growth compared to the control and were not infected with scab. It was proven that the ozone diffusion treatment was effective in exterminating soil pathogens living near the soil surface and in enhancing plant growth.

The Effect of Surface Barrier Discharge Plasma Products on the Germination of Cereals

Seeds of cereals (spring and winter wheat, winter triticale, and winter rye) were treated with products of surface barrier discharge plasma for various times (30 and 60 min) on exposure outside the zone of active discharge. It is established that the seeds of cereals tested differently responded to this treatment, which is probably related to the degree of their stability under oxidative stress conditions. The response to treatment of the seeds occurring outside the active discharge zone is manifested at greater times of exposure than in the case of direct treatment of seeds by the surface discharge products.

Characterization of Efficiency and Mechanisms of Cold Atmospheric Pressure Plasma Decontamination of Seeds for Sprout Production.

The consumption of fresh fruit and vegetable products has strongly increased during the past few decades. However, inherent to all minimally processed products is the short shelf life, and the risk of foodborne diseases, which have been increasingly related to such products in many parts of the world. Because of the favorable conditions for the growth of bacteria during the germination of seeds, sprouts are a frequent source for pathogenic bacteria, thus highlighting the need for seed decontamination to reduce the risk of foodborne illness. Consequently, this study focused on cold atmospheric pressure plasma (CAPP) treatment of artificially inoculated seeds in a diffuse coplanar surface barrier discharge to determine the inactivation efficiency for relevant foodborne pathogens and fungal spores. Plasma treatment of seeds resulted in a highly efficient reduction of microorganisms on the seed surface, while preserving the germination properties of seeds, at least for moderate treatment times. To characterize the mechanisms that contribute to microbial inactivation during plasma treatment, an experimental setup was developed to separate ultraviolet light (UV) and other plasma components. The combination of bacterial viability staining with confocal laser scanning microscopy was used to investigate the impact of ozone and other reactive species on the bacterial cells in comparison to UV. Further characterization of the effect of CAPP on bacterial cells by atomic force microscopy imaging of the same Escherichia coli cells before and after treatment revealed an increase in the surface roughness of treated E. coli cells and a decrease in the average height of the cells, which suggests physical damage to the cell envelope. In conclusion, CAPP shows potential for use as a decontamination technology in the production process of sprouts, which may contribute to food safety and prolonged shelf life of the product.

Improvement of Adhesion Properties of Polyamide 6 and Polyoxymethylene-Copolymer by Atmospheric Cold Plasma Treatment.

A study is presented on cold plasma treatment of the surfaces of two engineering polymers, polyamide 6 (PA6) and polyoxymethylene (POM-C), by diffuse coplanar surface barrier discharges under atmospheric air conditions. We found that plasma treatment improved the adhesion of both polymers for either polymer/polymer or polymer/steel joints. However, the improved adhesion was selective for the investigated adhesive agents that were dissimilar for the two studied polymers. In addition, improvement was significantly higher for PA6 as compared to POM-C. The observed variation of the adhesion was discussed in terms of the changes in surface chemistry, wettability and topography of the polymer surface.

Cold Atmospheric Pressure Plasma Can Induce Adaptive Response in Pea Seeds

This study investigated the effect of cold atmospheric pressure air plasma pre-treatment on pea (Pisum sativum L.) seeds. The aim of our study was to verify the plasma impact on DNA damage and the induction of positive adaptive response in pea seedlings. The pea seeds were treated by plasma at the exposure times ranging from 60 to 300 s. Plasma was generated using the coplanar type of dielectric surface barrier discharge. The main plasma properties were estimated by electrical and by optical emission spectroscopy measurements. The DNA damage was evaluated by the alkaline comet assay. The adaptive response on seedlings was tested using the toxic concentration of zeocin. The positive effect of plasma pre-treatment and the reduction of DNA damage of pea seedlings in comparison to control samples without plasma was observed at all exposure times used. The strongest repairing effect was observed at the plasma treatment time in the range from 120 to 240 s. These results verify the safety of plasma application in agriculture at germination and growth enhancement and the existence of a plasma induced adaptive response.

Inhibition or Stimulation of Ochratoxin A Synthesis on Inoculated Barley Triggered by Diffuse Coplanar Surface Barrier Discharge Plasma.

Ochratoxin A (OTA) is one of the most abundant food-contaminating mycotoxins. Besides their high toxicity, mycotoxins are highly stable to physical, chemical or biological detoxification. Therefore, the treatment with cold atmospheric plasma could be one approach to reduce the amount of mycotoxins in different products. The aim of this study was to determine the influence of cold atmospheric plasma on the inactivation of Aspergillus niger and Penicillium verrucosum inoculated on barley and their production of OTA. Inoculated barley was treated with plasma generated by dry air, CO2 or CO2 + O2 for 1 or 3 min and stored for up to two weeks at 9, 25, or 37°C. Three minutes of air plasma treatment effectively significantly reduced the total mold count of both microorganisms by 2.5–3 log cycles. The production of OTA from A. niger was only low, therefore the treatment effect was indistinguishable. The treatment of P. verrucosum on barley after an incubation of five days using a CO2 + O2 plasma resulted in a reduction of the OTA content from 49.0 (untreated) to 27.5 (1 min) and 23.8 ng/g (3 min), respectively. In contrast, CO2 plasma caused an increase of the OTA amount from 49.0 (untreated) to 55.8 (1 min) and 72.9 ng/g (3 min). Finally, the use of air plasma resulted likewise in a decrease of the OTA concentration from 56.9 (untreated) to 25.7 (1 min) and 20.2 ng/g (3 min), respectively. Reducing the incubation time before the treatment to 24 h caused in contrast an increase of the OTA content from 3.1 (untreated) to 29.1 (1 min) and 20.7 ng/g (3 min). Due to the high standard deviation, these changes were not significant, but the tendencies were clearly visible, showing the strong impact of the plasma gas on the OTA production. The results show, that even if the total mold count was reduced, under certain conditions the OTA amount was yet enhanced, probably due to a stress reaction of the mold. Concluding, the plasma gas and incubation conditions have to be considered to allow a successful inactivation of molds and in particular their toxic metabolites.

Improved microstructure of alumina ceramics prepared from DBD plasma activated powders

Submicron Al2O3 powders were activated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) plasma. The influence of the plasma treatment on the powder properties and their impact on the microstructure of dry and wet shaped ceramics were investigated. Raman and FTIR analyses of treated powders showed a substantial increase of the powder’s surface hydroxylation, surface cleaning, and the presence of adsorbed NOx originating from the DCSBD. Sintering of the dry shaped plasma treated powders did not influence sintering behavior. On the other hand, the plasma treated powder was able to form stable water suspension without any chemical stabilization aid. Slip cast samples exhibited finer pore size distribution, a higher sinterability, and a finer final microstructure. The grain size of slip casted plasma treated powder was reduced by a factor of 1.7, which facilitated a grain size of 0.68 μm at the relative density of 99.54% t.d. obtained by pressure-less sintering.

Numerical investigation of nanosecond pulsed plasma actuators for control of shock-wave/boundary-layer separation

This study numerically explores the flow physics associated with nanosecond pulsed plasma actuators that are designed to control shock-wave induced boundary-layer separation in a Mach 2.8 supersonic flow. By using two dielectric barrier surface discharge actuator configurations, parallel and canted with respect to the flow velocity vector, a previous experiment suggested that the actuator worked in two ways to influence the interaction: boundary layer heating and vorticity production. The heating effect was enhanced with the parallel electrode and made the boundary-layer separation stronger, while the canted electrode produced vorticity and suppressed the boundary-layer separation due to the momentum transfer from the core flow. Because the detailed physical processes are still unclear, in this paper a numerical investigation is undertaken with a large eddy simulation and an energy deposition model for the plasma actuation, in which the dielectric barrier discharge produced plasma is approximated as a high temperature region. The flow characteristics without the plasma actuation correspond to the experimental observation, indicating that the numerical method successfully resolves the shock-wave/boundary-layer interaction. With the plasma actuation, complete agreement between the experiment and calculation has not been obtained in the size of the shock-wave/boundary-layer interaction region. Nevertheless, as with the experiment, the calculation successfully demonstrates definite difference between the parallel and canted electrodes: the parallel electrode causes excess heating and increases the strength of the interaction, while the canted electrode leads to a reduction of the interaction strength, with a corresponding thinning of the boundary layer due to the momentum transfer. The counter flow created by the canted actuator plays an important role in the vortex generation, transferring momentum to the boundary layer and, consequently, mitigating the shock induced boundary layer separation.

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge (V-SBD) excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge (d = 0 mm) and volume added surface barrier discharges (d = 2 mm and 3 mm). The optical emission spectra are recorded for calculating emission intensities of N2 (C3Πu → B3Πg) and (B2 → X2 ), and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d = 0 mm structure can excite the largest emission intensity of N2 (C3Πu → B3Πg), while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of (B2 → X2 )/N2 (C3Πu → B3Πg) during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d = 3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N2 (C3Πu → B3Πg) than that of d = 2 mm structure. The structure of d = 2 mm can maintain more increasing factor than that of the d = 3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.

Decrease of the surface pH of maple and the production of nitrate by three pulsed dielectric barrier discharges

In this study, the influence of dielectric barrier discharges at atmospheric pressure on maple sapwood was analyzed. Three common discharge types, a coplanar surface barrier discharge (CSBD), a direct dielectric barrier discharge and a jet discharge/remote plasma, were realized by the same electrodes and power supply. In general, plasma treatments are known to modify various surface properties leading to improved adhesion. For resins such as urea formaldehyde, the curing behavior is dependent on the pH. Therefore, the change of the surface pH value of maple is measured. As the main product of plasma-generated nitrogen oxides, the nitrate concentrations and consequently the nitric acid concentrations of the surfaces were determined. A significant pH reduction from about pH 5.6 to pH 4.6 was reached after a 30 s plasma treatment. An increase in the nitrate concentration over the plasma treatment duration was measured for all three discharges with a maximum of 6.6 mg/L for the CSBD, which corresponds to a concentration of 8.25 mg per m2 wooden surface.

The Effect of Plasma Pretreatment and Cross-Linking Degree on the Physical and Antimicrobial Properties of Nisin-Coated PVA Films.

Stable antimicrobial nisin layers were prepared on the carrying medium-polyvinyl alcohol (PVA) films, crosslinked by glutaric acid. Surface plasma dielectric coplanar surface barrier discharge (DCSBD) modification of polyvinyl alcohol was used to improve the hydrophilic properties and to provide better adhesion of biologically active peptide-nisin to the polymer. The surface modification of films was studied in correlation to their cross-linking degree. Nisin was attached directly from the salt solution of the commercial product. In order to achieve a stable layer, the initial nisin concentration and the following release were investigated using chromatographic methods. The uniformity and stability of the layers was evaluated by means of zeta potential measurements, and for the surface changes of hydrophilic character, the water contact angle measurements were provided. The nisin long-term stability on the PVA films was confirmed by tricine polyacrylamide gel electrophoresis (SDS-PAGE) and by antimicrobial assay. It was found that PVA can serve as a suitable carrying medium for nisin with tunable properties by plasma treatment and crosslinking degree.

Unexpected rotational distribution of the ground electronic state OH(X 2Π) generated by plasma at the interface with liquid water

An unexpected rotational distribution of the ground electronic state OH(X 2Π) was observed by laser-induced fluorescence in a surface barrier discharge in contact with a liquid water interface. Analysis assuming a Boltzmann distribution yielded an unrealistically high rotational temperature above 600 K in the post-discharge phase. This is interpreted as a quasi-Boltzmann rotational distribution that is not in equilibrium with the translational temperature of the background gas. While the peculiarities of rotational distribution of excited OH(A 2Σ+) are known, the presented results show that even the ground electronic state OH(X 2Π) does not always have to be a reliable indicator for spectroscopic thermometry in plasmas containing water. A series of similar observations challenges the usual approach in kinetic models, when the rotational distribution is assumed to follow the Boltzmann function with the temperature of surrounding gas.

On the Determination of the Initial Ignition Voltage of a Surface Discharge in Air

The experimental and calculated values of the initial ignition voltage of a surface barrier discharge in atmospheric air in a plane–parallel electrode system with a Plexiglas barrier are presented. It is shown that the calculation of the initial voltage based on a simplified procedure, in which the criterion of the discharge initiation is the realization of the Townsend condition, provides the calculated dependence of the initial voltage on the barrier thickness, which coincides with the experimental data.

Cold Plasma: The Way to Improve the Repeatability of Sald ICP-MS Analysis

Abstract This work deals with the preparation of model biological microsamples for Substrate-Assisted Laser Desorption Inductively Coupled Plasma Mass Spectrometry (SALD ICP-MS). This technique provides the direct and fast analysis of liquid samples deposited onto polyethylene terephthalate (PET) plates (substrates) in the form of dried droplets with minimal sample preparation and submicrolitre sample volume requirements. Furthermore, SALD ICP-MS allows for the direct analysis of samples in organic solvents, which cannot be directly nebulised to ICP-MS. These benefits are, however, balanced out by the low degree of repeatability of the assay, which is typically about 30%. One of the approaches to increase the repeatability is a modification of the substrate surface by Diffuse Coplanar Surface Barrier Discharge (DCSBD) with the addition of an internal standard to the sample. Using this approach, a relative standard deviation (RSD) of less than 10% for model biological samples can be achieved. The only limitation of this technique is the occurrence of the so-called “aging effect”, i.e. the gradual return of the modified physicochemical surface properties to their original state

Effect of Cold Atmospheric Pressure Plasma on Maize Seeds: Enhancement of Seedlings Growth and Surface Microorganisms Inactivation

Cold atmospheric pressure ambient air plasma generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) was investigated for inhibition of native microbiota and potentially dangerous pathogens (Aspergillus flavus, Alternaria alternata and Fusarium culmorum) on the maize surface. Moreover, the improvement of germination and growth parameters of maize seeds was evaluated. Maize (Zea mays L.; cv. Ronaldinio), one of the most important cultivated crops worldwide, was selected as the research material. Electrical measurements confirmed the high volume power density (80 W cm−3) of DCSBD plasma. Non-equilibrium plasma state evaluated using optical emission spectroscopy showed values of vibrational and rotational temperature (2700 ± 300) K and (370 ± 75) K, respectively. Changes on the plasma treated seeds surface were studied by water contact angle measurement, scanning electron microscope analysis and Fourier transform infrared spectroscopy. A complete devitalisation of native microbiota on the surface of seeds was observed after a short treatment time of 60 s (bacteria) and 180 s (filamentous fungi). The plasma treatment efficiency of artificially contaminated maize seeds was estimated as a reduction of 3.79 log (CFU/g) in F. culmorum after a 60-s plasma treatment, 4.21 log (CFU/g) in A. flavus and 3.22 log (CFU/g) in A. alternata after a 300-s plasma treatment. Moreover, the obtained results show an increase in wettability, resulting in a better water uptake and in an enhancement of growth parameters. The investigated DCSBD plasma source provides significant technical advantages and application potential for seed surface finishing without the use of hazardous chemicals.

Influence of atmospheric pressure plasma jet and diffuse coplanar surface barrier discharge treatments on wood surface properties: A comparative study

Beech and larch substrates were successfully treated by an atmospheric pressure plasma jet (APPJ) or a diffuse coplanar surface barrier discharge (DCSBD) system. Applying both technologies on wood, more hydrophilic properties were achieved, potentially by the degradation of hydrophobic extractives, the generation of polar functional groups and a modification of surface roughness. Comparing both plasma systems, the hydrophilization effect was stronger using the APPJ. The formation of polar groups on the surface was detected by X–Ray photoelectron spectroscopy. Investigated by scanning electron microscopy, APPJ further showed a more distinct impact on surface morphology compared to DCSBD. Following natural aging, plasma treatment effects such as hydrophilicity were partially reduced and the recovery was more pronounced for larch wood compared to beech.

Cold plasma treatment triggers antioxidative defense system and induces changes in hyphal surface and subcellular structures of Aspergillus flavus.

The cold atmospheric-pressure plasma (CAPP) has become one of the recent effective decontamination technologies, but CAPP interactions with biological material remain the subject of many studies. The CAPP generates numerous types of particles and radiations that synergistically affect cells and tissues differently depending on their structure. In this study, we investigated the effect of CAPP generated by diffuse coplanar surface barrier discharge on hyphae of Aspergillus flavus. Hyphae underwent massive structural changes after plasma treatment. Scanning electron microscopy showed drying hyphae that were forming creases on the hyphal surface. ATR-FTIR analysis demonstrated an increase of signal intensity for C=O and C-O stretching vibrations indicating chemical changes in molecular structures located on hyphal surface. The increase in membrane permeability was detected by the fluorescent dye, propidium iodide. Biomass dry weight determination and increase in permeability indicated leakage of cell content and subsequent death. Disintegration of nuclei and DNA degradation confirmed cell death after plasma treatment. Damage of plasma membrane was related to lipoperoxidation that was determined by higher levels of thiobarbituric acid reactive species after plasma treatment. The CAPP treatment led to rise of intracellular ROS levels detected by fluorescent microscopy using 2',7'-dichlorodihydrofluorescein diacetate. At the same time, antioxidant enzyme activities increased, and level of reduced glutathione decreased. The results in this study indicated that the CAPP treatment in A. flavus targeted both cell surface structures, cell wall, and plasma membrane, inflicting injury on hyphal cells which led to subsequent oxidative stress and finally cell death at higher CAPP doses.

Surface modification of highly porous 3D networks via atmospheric plasma treatment

Tetrapodal ZnO (T‐ZnO) and aerographite networks represent two highly open porous (94.6 and 99.96%, respectively) model materials on which the impact of an atmospheric‐pressure plasma was studied for the first time. The air plasma treatment by a surface barrier discharge caused remarkable surface modifications on the T‐ZnO template, leading to a large number of oxygen vacancies. These observations were made using scanning electron microscopy (SEM) and Raman spectroscopy. In the second proposed set‐up, pellets of aerographite material were processed to a plasma jet with pressurized air and nitrogen. Hexamethyldisiloxane (HMDSO) was introduced as a precursor into the effluent jet for nanoparticle deposition. Opposing trends in atomic concentrations versus distance to the plasma source were observed when the gas (nitrogen or pressurized air) was changed. More pronounced nanoparticle coverage occurred in the pressurized air plasma. Their distribution was studied using SEM, energy‐dispersive X‐ray (EDX), and Raman spectroscopy. Because of the higher oxidation in the pressurized air plasma treatment, the deposited nanostructures appeared to be a mixture of Si and SiOx nanoparticles.

(Invited) Plasma Biofilm Decontamination: What Happens to the Underlying Surface?

In natural and manmade environments, bacterial biofilms are ubiquitous, yet the significance of biofilm contamination in a clinical setting is often underestimated [1]. Such contamination presents a particularly virulent form of infection that is shielded from systemic antibiotics, providing ideal conditions for the emergence of multidrug-resistant colonies [2]. There is an unprecedented need to establish new strategies to manage the colonization of clinical surfaces with these complex bacterial communities. This contribution explores the use of cold atmospheric pressure air plasma for the inactivation of clinically relevant biofilms grown on medical grade titanium. Furthermore, the impact of the plasma treatment on the properties of the host surface is investigated. Using a 1D air plasma model [3], supported by experimental measurements, the chemistry of a Surface Barrier Discharge (SBD) suitable for biofilm inactivation was shown to contain a wealth of long-lived species such as O3, NO2 and N2O. Under the influence of a convective flow, the presence of species that are traditionally considered to be too short-lived to reach a downstream sample are predicted, e.g. OH. [4] The SBD system, shown in Figure 1, was found to be highly effective for the decontamination of single and mixed species biofilms, achieving a multiple log reduction within 60 seconds of exposure. Given that the surface composition and morphology are key factors influencing biofilm formation, the impact of the plasma decontamination process on the surface characteristics was assessed and shown to induce considerable changes. The impact of these changes on the ability of bacteria to adhere to plasma treated titanium surfaces was examined. It was shown that biofilm formation on surfaces subjected to the plasma treatment was found to be accelerated in comparison to untreated surfaces. This study demonstrates that cold air plasma is an effective tool for biofilm elimination on clinically relevant surfaces, yet the choice of plasma system must be carefully considered as such treatments can significantly alter the ability of bacteria to attach to the surface. [1] D. Lindsay, A. von Holy, Journal of Hospital Infection. 64, (2006), 313-25. [2] J. Davies, D. Davies, Microbiol Mol Biol Rev. 74, (2010) 417. [3] M. Hasan, J. L. Walsh, J. Appl. Phys. 119, (2016), 203302. [4] M. Hasan, J. L. Walsh, Appl. Phys. Lett. 110, (2017), 134102. [5] Y. Ni, Y., M.J. Lynch, M. Modic, R.D. Whalley, J.L. Walsh. Journal of Physics D: Applied Physics, 49 (35), 355203 (2016). Figure 1