Pressure Air Plasma Research Articles

Experimental Studies on Applications of Atmospheric Pressure Air Plasma for Eco-friendly Processing of Textiles and Allied Material

Experimental Studies on Applications of Atmospheric Pressure Air Plasma for Eco-friendly Processing of Textiles and Allied Material

Atmospheric-pressure plasma treatments of NBR for the improvement of adhesion in footwear applications

Strong adhesion between the sole and the upper part of shoes is necessary to maintain their integrity and protect the foot from external conditions. Vulcanized rubbers are commonly used for sole manufacturing but, because of their nonpolar nature, they need to be conditioned before bonding. In this work, atmospheric-pressure air plasma treatments on flat and mechanically roughened nitrile butadiene rubber (NBR) were studied as environmentally friendly alternatives to the usual halogenation process to improve the adhesion between NBR and leather parts. Surface activation and coatings by plasma-polymerization of (3-aminopropyl) triethoxysilane were used, and the evolution of their effectiveness during the following 30 days was studied. Both treatment types achieved bond strengths that were greater than those of the untreated NBR. Coating treatments caused an initial increase in the surface polar carbon-oxygen species, which was kept for at least the following 6 days and allowed for an improvement of the bond strength when the coatings were bonded with the leather within that period. However, the presence of these species on the coatings decreased during storage, resulting in weaker adhesion than that of the untreated NBR before the end of the aging study. The most durable effectiveness (30 days) was shown by plasma-activated, mechanically roughened NBR. Chemical and morphological characterizations suggested that this durable adhesion improvement was due to ablation by the plasma irradiation, which had a roughening effect at a microscopic scale, additionally to the macroscopic effects of mechanical roughening.

Characterization of an atmospheric pressure air plasma device under different modes of operation and their impact on the liquid chemistry

It has been shown that plasma generated in contact with liquid can be tailored to tune the composition of plasma functionalized liquids. For biomedical applications, it is necessary to understand the generation of the plasma treated liquids to modulate the composition and thus the biological response. In this work, two distinct discharge compositions were realized by modifying the location of the ground electrode in a pin-to-liquid plasma system. Through this simple modification to the configurations, the spatiotemporal characteristics of the discharge were significantly affected which, in turn, affected the composition of the generated plasma activated water (PAW). Colorimetric testing of the PAW generated from each system revealed that only one configuration was able to generate PAW with a high concentration of H2O2. Using time-, space-, and wavelength-resolved imaging of excited plasma species [OH, N2 (SPS), N2+ (FNS), and atomic O], the differences in PAW composition were linked to the differences observed in the discharge dynamics between the two configurations.

Enhancement Propagation of Protocorms in Orchid (Cymbidium tracyanum L. Castle) by Cold Atmospheric Pressure Air Plasma Jet

Propagation of orchid (Cymbidium tracyanum L. Castle) treated by using an air cold atmospheric pressure plasma jet at room temperature was investigated. The peak-to-peak voltage discharge and flow rate of the air atmospheric pressure plasma jet were set at 10.5 kV and 10 L/min, respectively. The constituent particles of the air cold atmospheric pressure plasma jet were revealed by optical emission spectroscopy. At the end of the jet nozzle, the constituent particles were observed, such as hydroxyl radical ˙OH, N2 first negative system (N2 1 −), N2s positive system (N2 2 +), and atomic oxygen. The average size, average number of buds, fresh and dry weights simultaneously increased by cold air plasma treatment compared with the control ones. The highest positive effects of treated protocorms on average size, average number of buds, fresh and dry weight were significantly improved by 238.2, 475.9, 85.6, and 152.5%, respectively. The transmission electron microscope showed the cytoplasmic cell wall in orchid protocorm disturbed by air cold plasma. Thus, the effects of constituent particles of air plasma might attack in the cell wall of protocorm leading to cell loosening, which improved elongation and released bud dormancy. These results indicated that the propagation of orchid protocorms depended on the effects of air cold plasma treatment with different plasma time durations.

Hemostasis Efficacy and Mechanism of Cold Atmospheric Air Plasma

The capacity of a cold atmospheric-pressure air plasma (CAAP) device for advanced first aid is presented. Using swine as an animal model, two trials: 1) a large, curved cut in hindquarters area and 2) amputation of a front leg, were performed. Cold atmospheric-pressure air plasma effluent, which carries reactive oxygen species (ROS) atomic oxygen (OI), is applied for wound treatments. Swift hemostasis of the wounds by the CAAP treatment was demonstrated. The pressure applied by a finger on the cut arteries in trial 1 and the tourniquet applied in trial 2 could be removed immediately after the treatment and there was no re-bleed in both cases. CAAP hemostasis mechanism was explored via in-vitro tests. The tests on sodium citrate mixed blood-droplet samples show that 1) the heat delivered by the CAAP has no impact on the observed clot formation, 2) plasma effluent activates platelets to promote coagulation state and cascade, and 3) the degree of clotting increases with the total amount of applied OI by means of the CAAP effluent. It took only 16 s of the CAAP treatment to reach full clotting, which was considerably shortened from the natural clotting time of about 25 minutes. The tests on smeared blood samples show that the reduction of the platelet count and the increase of RBC count are proportional to the amount of applied OI. A plausible CAAP hemostasis mechanism is concluded from the in vitro test results and the animal model trials.

Polarization spectroscopy for quantitative analysis of atmospheric CO2 and air plasma flows

This article demonstrates the feasibility of polarization spectroscopy as a diagnostic tool for quantitative analysis of atmospheric pressure plasma conditions. Atmospheric pressure air and CO2 plasma flows created in a microwave-powered plasma torch are investigated. A detailed line-by-line simulation approach is employed to interpret the polarization spectra recorded in the resonator of the plasma torch. The line-by-line code for the simulation of polarization spectroscopy of O2 Schumann–Runge has been developed and verified with measurements in atmospheric pressure O2 plasma for a previous study. In this study, this simulation code for O2 absorption is used to model the polarization spectra measured in CO2 plasma and determine the inner energy distribution of the molecules for the first time. The resulting vibrational and rotational temperatures are Tvib=6115K and Trot=2660K. In order to simulate measurements in air plasma, the line-by-line code is extended to enable two-species modeling using O2 Schumann–Runge as well as NOγ absorption. The new two-species simulation approach allows for the determination of the relative number density nO2/nNO=1500±100. This paper clearly demonstrates the value of polarization spectroscopy as a quantitative measurement technique for atmospheric pressure plasma applications.

Wheat gliadin in ethanol solutions treated using cold air plasma at atmospheric pressure

The physiochemical and functional properties of wheat gliadin in 70% ethanol treated with cold air atmospheric pressure plasma (CAAP) were measured, including its intermolecular structure, the proportion of free thiol groups and disulfide bonds, and molecular size distribution. The CAAP treatment decreased the pH and increased the electric conductivity of gliadin solution by generating the high-energy reactive oxygen and nitrogen species (RONS), including O3, H2O2, NO2− and NO3−. The increase in the β-sheets and the decrease in the α-helix and β-turns in CAAP-treated gliadin samples, which were measured using Fourier transform infrared (FT-IR) spectroscopy, were indicative of the conformational rearrangement compared with the untreated sample. The decrease of the peak intensity around 280 nm in the UV spectra suggested that CAAP could modify the aromatic amino acids of gliadin; this outcome was consistent with the results of the fluorescence peak profiles. The CAAP treatment increased the content of disulfide bonds and free thiol groups in gliadin. An increase in zeta potential and the size of gliadin and its colloidal particles were observed with the increased duration of the CAAP process. The increased foaming ability of gliadin colloidal particles was observed after CAAP treatment. Of all the CAAP treated samples, a better foam stability was shown in the 3 and 5 min-treated gliadin samples. These results suggested that the CAAP treatment might act as an effective technique to broaden the future utilizations of wheat gliadin in the food industry.

Measurement of nitrogen dioxide and nitric oxide densities by using CEAS (cavity‐enhanced absorption spectroscopy) in nonthermal atmospheric pressure air plasma

AbstractNonthermal atmospheric pressure plasmas are widely used in biomedicine and agriculture. Currently, radical density is used as an important parameter for the development of plasma biomedicine and agriculture. Especially, nitrogen dioxide (NO2) and nitric oxide (NO) radicals are significant species in these applications. These could be measured by using the cavity‐enhanced absorption spectroscopy (CEAS) technique. For the NO2 and NO radical density measurement, we used a visible LED (light‐emitting diode) of 660 nm and a mid‐infrared LD (laser diode) of 5238.6 nm, respectively. Radical densities can be calculated with the transmission ratio using Beer–Lambert law, which is obtained by the absorbed amount of laser intensity passed through the gas from the plasma jet in an optical cavity of CEAS.

Influence of Nonthermal Atmospheric Plasma-Activated Water on the Structural, Optical, and Biological Properties of Aspergillus brasiliensis Spores

Plasma-activated water (PAW) has emerged as a platform for sterilizing fungal pathogens. In this study, we investigated the influence of PAW on black melanized spores of Aspergillus brasiliensis to explore the mechanism of fungal spore inactivation. PAW was prepared by activating deionized water with a nonthermal atmospheric pressure air plasma jet (soft plasma jet). The concentrations of H2O2 and NOx in the PAW treated by the soft plasma jet for 3 min were 50 μM and 1.8 mM, respectively, and the pH of the PAW was 3.10. The reactive oxygen and nitrogen species (RONS) in the PAW increased with longer plasma activation time. After being treated for 30 min in the PAW with a plasma activation time of 3 min, the spore viability dramatically dropped to 15%. The viabilities of 0.3% H2O2- and 0.3% HNO3-treated spores were 22% and 42%, respectively. The breakage of the spore cell wall by the PAW was revealed in scanning electron microscope images and flow cytometry measurements. Disruption of cell wall integrity provides a path for intracellular components to escape and RONS of the PAW can attack intracellular components directly. Degradation of high molecular genomic DNA was also observed by agarose gel electrophoresis. These results suggest that long-lived reactive species generated in the PAW play an important role in the inactivation of melanized fungal spores. Consequently, PAW produced by a soft plasma jet can be applied to sterilize bioprotective walled fungal spores in a relatively large volume.

Inactivation of virus and bacteria using cold atmospheric pressure air plasmas and the role of reactive nitrogen species

Cold atmospheric pressure plasma has potential as a non-thermal processing technology to decontaminate food and food contact surfaces due to its ability to generate an abundance of reactive oxygen and nitrogen species with antimicrobial attributes at ambient conditions. In this study, we present a comparison on the effectiveness of surface decontamination against feline calicivirus (FCV) and Salmonella spp using four different plasma sources, a dielectric barrier discharge (DBD) in direct contact with the substrate and three remote plasma treatment sources: a 2D DBD, a volumetric DBD and a gliding arc discharge. The plasma sources were all operated in air at atmospheric pressure. The decontamination efficacy was enhanced by the presence of humidity on the sample surface and only direct contact between plasma and samples allowed the inactivation of pathogens on dry substrates. Across all sources, FCV was seen to be more susceptible to the plasma-generated species than Salmonella spp. The diminished effectiveness of the gliding arc discharge compared to the DBDs operating at the same power is most likely due to the low Henry’s law constant of NO, the dominant reactive species generated by the gliding arc. Control experiments illustrate that the co-existence of O3 and NO2, as in the afterglow of the remote DBDs enhances the inactivation compared to the inactivation by O3 or NO2 only. A chemical kinetics model of the plasma effluent and the plasma treatments show a strong correlation between the gas-phase concentration of N2O5 and inactivation of the virus. We experimentally show that the production of N2O5 coincides with the enhanced generation of reactive nitrogen species in the liquid phase.

Rapid inactivation of airborne porcine reproductive and respiratory syndrome virus using an atmospheric pressure air plasma

AbstractThe transmission of airborne diseases in animals poses great risks to animal safety with potential significant economic losses. In this study, we report on the use of a dielectric barrier discharge (DBD) for in‐flight inactivation of an airborne aerosolized porcine reproductive and respiratory syndrome virus. The infectivity of the sampled virus downstream compared to upstream of the DBD reactor as determined by the TCID50 method showed a ∼3.5 log10 reduction in the virus titer. Independent testing of the viral genome by the reverse‐transcription quantitative real‐time polymerase chain reaction method confirmed the inactivation with minimal filtering effects. Both short‐lived species such as and and peroxynitrous acid (ONOOH) chemistry at low pH in the virus‐laden droplets are suggested to be responsible for the observed inactivation.

Atmospheric air plasma jet for improvement of paint adhesion to aluminium surface in industrial applications

Improvement of paint adhesion to aluminium surfaces is one of the main challenges in many industrial applications. In this paper, we introduce the atmospheric pressure air plasma jet as an appropriate candidate for preparation of 5052 aluminium surface alloy to improve paint adhesion in the industrial level. The employed plasma jet can promote paint adhesion to aluminium surface at the treatment velocity of 2 m/min and plasma size of 10 mm. Based on the cross-cut test, adhesion of polyurethane paint to the surface greatly increases from 1B to 5B level due to the plasma treatment. According to the results, the surface wettability increases under the influence of the plasma treatment so that water droplet contact angle reduces from 79.0°±2.0°–27.5°±2.0° after the treatment. Dyne test ink also denotes the increment of surface energy to the greater than 72 mN/m. Besides, we employ various analytical methods to investigate the physical and chemical changes arise from the plasma processing to the surface. Atomic force microscopy (AFM) results show a twofold increase in the roughness parameters of plasma treated surface which can result in a stronger paint and surface interlocking. Chemical analysis of the surface reveals that plasma treatment of the aluminium surface leads to the surface cleaning and formation of hydrophilic functional groups that attract much more water towards the surface and improves the paint adhesion.

Atmospheric pressure microwave plasma for aluminum surface cleaning

An atmospheric pressure, 2.45 GHz microwave plasma operating in ambient air was used to clean and activate aluminum surfaces. The effect of processing parameters on surface chemistry of aluminum has been studied to determine the minimal power and time needed to create clean surfaces. The contact angle measurements showed that the hydrophilicity greatly increases with increasing power and decreasing substrate speed. Fourier transform infrared spectroscopy shows that oxidative and thermal degradation is present during the plasma cleaning process. The authors’ system using atmospheric pressure air plasma proves to be an efficient method for cleaning and activating metal surfaces without generating chemical waste and can be used to increase the adhesion of subsequent protective coatings.

A COMPARATIVE STUDY OF PHOTOCATALYTIC ACTIVITY OF ZnO-BASED PHOTOCATALYSTS TREATED BY DIELECTRIC BARRIER DISCHARGE PLASMA

Low-temperature plasma treatment has shown great advantages in many fields of catalytic application. In the previous study, it has been concluded that the performance of a dielectric barrier discharge (DBD) plasma-treated ZnO-based photocatalyst is superior to that of radiofrequency plasma-treated and untreated ones. In this study, the effect of plasma conditions on the performance of the ZnO-based photocatalyst was investigated from the aspects of discharge energy and treatment time. Atmospheric-pressure air plasma generated by dielectric barrier discharge was applied to treat commercially available ZnO microparticles. To elucidate the plasma treatment effects, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used for catalysts characterization. The photocatalytic activities of untreated and plasma-treated ZnO microparticles were evaluated by measuring the photodegradation of methyl orange. The photocatalytic activity, expressed in terms of rate constants of photodegradation of methyl orange, was approximately 8 times higher for the most active sample than that for untreated ZnO. The maximal value of rate constant was found to be 1.1·10-2 s-1. The effective energy consumed by the most active catalyst during treatment time was found to be 3180 J. The results of diffuse reflectance infrared Fourier transform spectroscopy and dark adsorption experiments imply that molecules of methyl orange and oxygen-containing functionalities, e.g., hydroxyl groups, seem compete for adsorption sites on the surface of the catalyst. The most active catalysts showed the highest adsorption capacity for methyl orange and low ability to adsorb the hydroxyl groups.

On the air atmospheric pressure plasma treatment effect on the physiology, germination and seedlings of basil seeds

Basil (Ocimum basilicum) seeds were treated for different exposure times with a non-equilibrium plasma produced by a volume dielectric barrier discharge in humid air at atmospheric pressure.Plasma treatment did not change the seed structure and morphology, as visualized by high-resolution computed x-ray microtomography. A faster and higher germination rate was observed with plasma treatment of 1 and 3 min. Plantlets grown in sand, after both 2 and 3 weeks, showed a more developed root apparatus and better biometric parameters, compared to plants developing from non-treated seeds.After the plasma treatment, internal redistribution of macro and micronutrients was observed by using micro x-ray fluorescence spectroscopy. In particular P, K and Mg concentrated in the radicle, moving from the endosperm and cotyledons, while Zn, initially concentrated in specific tissues of the cotyledon, appeared more homogeneously distributed inside the whole seed after the plasma treatment. Significant variations in electrical impedance spectra were also observed after plasma treatment.This element redistribution in the seed was caused by the intense electrical field generated by the volume dielectric barrier discharge plasma, causing a movement of important micro and macronutrients from the storage regions of the seed towards the radicle tissues. This ion movement could explain the observed faster germination of the plasma-treated seeds. Indeed, such movement of ions is similar to what is generally observed in seed tissues during germination. The plasma treatment therefore somehow anticipates and implements the mobilization of key nutrients towards the radicle, resulting in faster and higher germination of the seeds as well as improved characteristics of the basil plantlet, especially at the root level.

Hydrophobic behavior of cotton fabric activated with air atmospheric-pressure plasma

Plasma treatment is known as a new technology applied on textile surface allowing the modification of their chemical properties. In our study, we have activated a cotton fabric surface with air atmospheric plasma. The wettabilty measurements, in terms of water contact angle and capillarity, reveal the hydrophobic behavior of cotton surface after plasma treatment under the studied conditions. The water contact angle increases from 60° for the untreated sample to 128° after 1 week from plasma activation. The capillarity of the plasma-treated surface reaches 42% instead of 72% for the untreated one. The chemical, morphological and physical modifications of cotton surface were also investigated before and after plasma activation.

Interaction of Plasma Jet With Methanol as Fundamental Processes in Solution

Plasma depollution is a relatively new field that investigates potential applications of atmospheric pressure plasma in environmental engineering, such as microorganism inactivation and degradation of organic molecules in water. In order to enunciate mechanisms of degradation of organic matter at molecular or atomic levels, the interaction between He, N2, O2, and air plasma jet and methanol in water was analyzed by gas chromatography–mass spectrum and Fourier transform infrared spectroscopy. Results show that the efficiency of methanol degradation is strongly dependent on the working gas and plasma treatment time. Compared to atmospheric pressure N2, O2, and air plasma jet, the He plasma jet may be utilized to degrade methanol more efficiently in aqueous solution. The efficiencies of degradation of methanol in water can be well described by using the chemical reaction rate model, where reactive oxygen and hydroxyl radical species play crucial roles in the degradation process. This paper provides an insight into the mechanism of degradation of organic pollutant in water by plasma.

Spore Viability and Cell Wall Integrity of Cordyceps pruinosa Treated with an Electric Shock-Free, Atmospheric-Pressure Air Plasma Jet

Atmospheric-pressure A r plasma jets are known to be detrimental to Cordyceps pruinosa spores. However, it is not clear what kinds of reactive species are more effective with regard to fungal cell death. Herein, we study which reactive species plays pivotal roles in the death of fungal spores using an electric shock-free, atmospheric-pressure air plasma jet, simply called soft plasma jet. Plasma treatment significantly reduced the spore viability and damaged fungal DNA. As observed from the circular dichroism spectra, scanning electron microscope images, and flow cytometric measurements, cell wall integrity was decreased by reactive oxygen and nitrogen species (RONS) from the plasma itself and the plasma-activated water. Consequently, degradation of the spore cell wall allows RONS from the plasma to reach the intracellular components. Such plasma-induced intracellular RONS can attack spore DNA and other intracellular components, as confirmed by electrophoresis analysis and phosphorylated histone measurement. In addition, weakening of the spore cell wall allowed for the loss of intracellular components, which can lead to cell death. Plasma radicals were investigated by measuring the optical emission spectrum of the soft plasma jet, and intracellular reactive oxygen species were confirmed by measuring the fluorescence of 2′, 7′-dichlorodihydrofluorescein-diacetate ( H 2 D C F - D A )-stained spores. The soft plasma jet generated considerable amounts of H 2 O 2 and N O x but a very small number of O H radicals as compared to the atmospheric-pressure A r plasma jet; this indicates that plasma-induced long-lived reactive species ( H 2 O 2 and N O x ) play an important role in the weakening of spore cell walls and cell death.

Deposition of TiO2 Thin Films on Wood Substrate by an Air Atmospheric Pressure Plasma Jet

In the present work, titanium dioxide (TiO2) coatings were deposited on wood surfaces by an atmospheric pressure plasma jet using titanium tetraisopropoxide (TTIP) as a precursor to improve the wood’s stability against ultraviolet (UV) light and its moisture resistance capability. The surface topology and morphology of the wood specimens were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface chemical compositions of the specimens were characterized by X-ray photoelectron spectroscopy (XPS) and by Fourier transform infrared (FTIR) spectroscopy. The wettability of the coated wood was investigated by measuring the sessile contact angle. SEM and AFM showed the presence of small globules of TiO2 with some areas agglomerated on the coated wood surface. The coated surface roughness increased with increasing deposition time. FTIR analysis showed the existence of a Ti–O–Ti band at 800–400 cm−1 on the coated wood surfaces. The results obtained from FTIR were confirmed by XPS measurements. The hydrophilic wood surfaces were transformed to become hydrophobic or superhydrophobic after coating with TiO2, depending on the deposition parameters. The changes of colour during UV-exposure for both uncoated and coated wood specimens were measured using the CIELab colour system. The TiO2 coated wood became more resistant to colour change after UV radiation exposure than did untreated wood.

Evaluation of atmospheric-pressure plasma parameters to achieve superhydrophobic and self-cleaning HTV silicone rubber surfaces via a single-step, eco-friendly approach

Effective self-cleaning and superhydrophobic surfaces having superb water repellency are among the most widespread alternatives for eliminating surface contamination, corrosion resistance, reducing ice accumulation, etc. to enhance the life-span of various engineered materials. In this study, we developed a simple methodology, based on an atmospheric-pressure air plasma system, as a simple, environmentally friendly and industry applicable approach for fabricating superhydrophobic surfaces. Our approach is significant as the use of an atmospheric-pressure plasma system combined with compressed air as an eco-friendly plasma gas offers great potential for the industrialization of superhydrophobic surfaces for mass production. The creation of micro- and nano-structured surface roughness on a low surface energy high temperature vulcanized (HTV) silicone rubber substrate resulted in a static water contact angle (WCA) > 160° and a contact angle hysteresis (CAH) < 3°. Scanning electron microscopy (SEM) revealed the presence of the plasma-induced coral-like micro- and nano-structures responsible for the superhydrophobicity of the surfaces. We assessed the influence of plasma operating parameters on the water repellency of silicone rubber via a design of experiment (DoE) method to determine the near-optimal operating parameters; once established, we could assess the characteristics of the surfaces. In addition to the superhydrophobic surfaces, we also fabricated another surface, named a slippery hydrophobic surface, under specific plasma operating conditions. Superhydrophobic surfaces prepared at these optimal plasma operating conditions showed favorable water repellency and self-cleaning properties under both wet and dry conditions.