Atmospheric Pressure Plasma System Research Articles

A remote atmospheric pressure plasma-assisted textile functionalization process on polymeric scaffolds for bone tissue engineering

When adopting polylactic acid (PLA) nonwoven for bone tissue engineering scaffolds, the inert and hydrophobic nature of PLA leads to poor biocompatibility and osteoconductivity, and limits the efficiency of applying bioceramic coatings, such as hydroxyapatite (HAp), for surface functionalization. To tackle these issues, a remote atmospheric pressure plasma (APP) system using a bespoke Pyrex chamber and acrylic acid monomer was designed and employed to functionalize the PLA via depositing carboxylic acid functional groups onto its surface. The remote APP showed being polymeric textile-suitable with an improved efficiency on not only immobilizing carboxylic acid functional groups on the PLA nonwoven than conventional systems but also the alternate soaking process for HAp deposition. Being compared with the neat PLA, the plasma-functionalized PLA exhibited a more hydrophilic surface (from 130.49 ± 1.28° to 117.40 ± 2.53°) with a 30-day stability (from 117.40 ± 2.53° to 119.40 ± 0.75°) and showed better biocompatibility (136 % to the neat PLA) with MC3T3-E1 mouse embryonic osteoblast cells after HAp deposition. The presence of carboxylic acid functional groups and HAp (Ca/P ratio of 1.7) was also identified using X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and a scanning electron microscope with energy dispersive X-ray analysis.

Biosafe removal of diclofenac from wastewaters by a continuous-flow mode cold atmospheric pressure plasma system

Diclofenac (DCF) is not only a versatile non-steroidal anti-inflammatory drug, but also an emerging water pollutant. There is an urgent need for innovative technology of wastewater treatment to reduce the impact of DCF on the environment. Thus, we examined the applicability of pulse-modulated radio-frequency atmospheric pressure glow discharge (pm-rf-APGD) for degradation of 1.56–50.0 mg L-1 DCF from both aqueous solutions and synthetic wastewaters. The removal rates varied from 84.0 ± 3.8% to 100.0 ± 0.1% for the aqueous solution and increased together with the decreasing concentration of DCF. For synthetic wastewaters, the DCF removal was enclosed in the range from 21.0 ± 1.0% to 74.8 ± 0.1%. The energy efficiencies varied from 0.0116 to 0.312 g kW-1h-1 for aqueous solutions and from 0.00779 to 0.0087 g kW-1h-1 for synthetic wastewaters, respectively. By application of ultraperformance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) and gas chromatography-mass spectrometry (GC-MS), the pm-rf-APGD-driven DCF degradation pathways were revealed to involve decomposition, nitration, and dehalogenation reactions yielding dichloroaniline, nitro-diclofenac and 8-chlorocarbazole-1-acetic acid, respectively, before achieving the total decomposition of DCF to carbon dioxide, water, chlorides, nitrates and amines. Notable increases in the contents of the radicals, i.e., H2O2 in addition to NO2- and NO3-, were observed in the plasma-treated DCF solutions in contrast to the controls. Finally, no cytotoxic activity of the pm-rf-APGD-treated DCF solutions was demonstrated on model non-malignant human endothelial cells (HUVEC) and human immortalized keratinocytes (HaCaT). We anticipate that the described continuous-flow pm-rf-APGD-based reaction discharge system might be applied for biosafe removal of DCF from the effluents originating from wastewater treatment plants.

Catalytically enhanced direct degradation of nitro-based antibacterial agents using dielectric barrier discharge cold atmospheric pressure plasma and rhenium nanoparticles

The common utilization of antimicrobial agents in medicine and veterinary creates serious problems with multidrug resistance spreading among pathogens. Bearing this in mind, wastewaters have to be completely purified from antimicrobial agents. In this context, a dielectric barrier discharge cold atmospheric pressure plasma (DBD-CAPP) system was used in the present study as a multifunctional tool for the deactivation of nitro-based pharmacuticals such as furazolidone (FRz) and chloramphenicol (ChRP) in solutions. A direct approach was applied to this by treating solutions of the studied drugs by DBD-CAPP in the presence of the ReO4− ions. It was found that Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS), generated in the DBD-CAPP-treated liquid, played a dual role in the process. On the one hand, ROS and RNS led to the direct degradation of FRz and ChRP, and on the other hand, they enabled the production of Re nanoparticles (ReNPs). The produced in this manner ReNPs consisted of catalytically active Re+4, Re+6, and Re+7 species which allowed the reduction of –NO2 groups contained in the FRz and ChRP. Unlike the DBD-CAPP, the catalytically enhanced DBD-CAPP led to almost FRz and ChRP removals from studied solutions. The catalytic boost was particularly highlighted when catalyst/DBD-CAPP was operated in the synthetic waste matrix. Re-active sites in this scenario led to the facilitated deactivation of antibiotics, achieving significantly higher FRz and ChRP removals than DBD-CAPP on its own.

(Invited) Atmospheric Pressure Plasma Treatment of Materials

Technologies based on the use of non-equilibrium plasmas have become virtually irreplaceable in diverse application fields. These range from modification/functionalization of surfaces of medical implants, production of functional thin films or nanostructured materials, light generation, environmental remediation, ozone generation or sterilization/decontamination of surfaces. However, there is a clear trend in the last few decades to substitute low-pressure plasma systems with the ones operated at atmospheric pressure. The interest in atmospheric pressure plasmas is stimulated not only by the decrease in equipment costs by avoiding expensive pumping systems of conventional low-pressure plasma devices but also by the possibility to process objects non-compatible with vacuum conditions. The latter triggered off rapid development of brand new scientific fields – plasma medicine and plasma agriculture.In this work, we briefly review the main operational principles of atmospheric pressure plasma sources, as well as the advantages/drawbacks of atmospheric plasma for a better understanding of the capabilities and limitations of the atmospheric plasma processing technology compared with conventional low-pressure plasma processing technologies. Subsequently, the possible use of two common atmospheric pressure plasma systems - dielectric barrier discharges and atmospheric pressure jets - will be demonstrated on the selected examples. The main emphasis will be given to the issues connected with the control of the wetting/drying/condensation of liquids on plasma-treated polymers, use of plasma pre-treatment on metallization of surfaces or their improved biocompatibility, application of atmospheric pressure plasma for deposition of nanostructured thin films, treatment of seeds with an aim to improve their germination, and last, but not least, the attention will also be devoted to the removal of organic deposits/contaminants, including pathogens, from different types of surfaces.

Evaluation of plasma‐activated water characteristics and its process optimization

AbstractPlasma‐activated water (PAW) is an emerging technology for the disinfection of foods and it is also widely evaluated for its applications in medicine. The long‐lived reactive oxygen species such as hydrogen peroxide and ozone are mainly responsible for the disinfecting properties of Ar/O2 PAW. In this study, PAW characteristics were evaluated with respect to the process conditions and the post‐treatment time to understand the effect of process conditions and the time stability of PAW. PAW was generated using a continuous flow dielectric barrier discharge Ar/O2 atmospheric pressure plasma system at different PAW treatment times. PAW properties were evaluated based on the concentration of hydrogen peroxide, ozone, pH, and the disinfection of Escherichia coli. From the time stability analysis, it was found that the hydrogen peroxide was more stable than ozone in PAW when stored at room temperature for 2 days. The E. coli inactivation was mainly attributed to the H2O2 and ozone concentration than pH. The optimum process condition was found as 104 ml/min water flow rate, 20‐min treatment time and 4 slm gas flow rate for maximum reactive species concentration in PAW.Practical ApplicationsThere is a need for non‐chemical disinfection method of fresh fruits and vegetables, as the present chemical‐based disinfection methods are inefficient in controlling food‐borne outbreaks and the residual toxicity of these chemicals. Plasma‐activated water (PAW) is an emerging technology, which has the potential in disinfecting microorganisms. The aim of the work was to analyze the disinfection properties and the time stability of PAW. It is evident from the results that PAW is effective in disinfecting Escherichia coli and its reactive species degrade with time. This will facilitate the application of PAW as a disinfectant for fresh fruits and vegetables without any residual toxicity to the food and the environment. Further, from the optimization studies, understanding of the influence of process parameters on the PAW characteristics was derived which will be helpful to scale‐up of this technology.

Enhancement of discharge properties of atmospheric pressure plasma systems through trace radio-frequency oscillation control

In this work, we report a novel approach that enhances the plasma properties of non-equilibrium plasma under atmospheric pressure using dual-frequency excitation sources. Specifically, these effects are induced by a low frequency of 50 kHz and a higher radio frequency source of 2 MHz. The results show that the application of a small radio-frequency (RF) component in addition to a low-frequency (LF) source improved electron acceleration and thus allows for the excitation to be modulated—through enhancement and suppression of electron impact during each RF period. Electron densities are also enhanced due to the modulated electron impact excitation rate, without an observable increase in gas temperature. When the applied RF component is comparable in magnitude with the low frequency component, the discharge is dominated by influences from the RF component, where the RF electric field provides and improves stability and uniformity simultaneously. This allows for higher input power to be provided to the system.

Characterization of plasma chemistry for an optimized pulse resonance atmospheric-pressure plasma system

The paper deals with monitoring the plasma chemistry of an atmospheric plasma low-frequency AC power supply. The study is based on optical spectroscopy and electrical measurements as diagnostic methods. The work includes details of developing and operating an in-house made, non-thermal, dielectric-free atmospheric plasma system, built for biological and agriculture applications. The experimental results clearly show the cross-dependence of the measured outputs (O3, O2, N2) and a wide range of process parameters (duty cycle, discharge frequency, voltage, etc.). A design-of-experiment approach is taken for phase-resolved optical emission spectroscopy of oxygen and nitrogen spectral lines/bands. The new plasma system allows an increase in the plasma-surface interaction selectivity and reduces plasma-induced damages to the surface.

Microwave Plasma System for Continuous Treatment of Railway Track

Braking conditions are a fundamental issue for the railway and have been a limiting factor in network capacity and timetabling. Leaf fall, especially during the autumn season, creates low-adhesion problems on railways, causing braking problems for trains. To address the requirements of the novel plasma industrial applications towards environmental applications, this work developed and tested a 2.45 GHz microwave atmospheric pressure plasma system for in situ removal of the third body layer deposited onto the railway so as to improve braking. The plasma reactor consisted of a 15 kW, 2.45 GHz magnetron-based microwave generator and a plasma reactor (dielectric tube placed in a TE01 monomode microwave cavity); the atmospheric plasma ignited and sustained at different power levels (2–15 kW) in different gases (nitrogen, argon) as well as mixtures of these gases with reactive molecules (water, oxygen) was jetted directly onto the railhead as to change the conditions for the wheel–rail interface. This technology is hoped to be a game-changer in enabling predictable and optimized braking on the railway network. Challenges encountered during the demonstration phase are discussed. Subsequent work should validate the results on a working railway line during the autumn season.

Multiphysics modeling of metal surface cleaning using atmospheric pressure plasma

An atmospheric pressure plasma (APP) system offers advanced, cost-effective processing routes for surface cleaning without a vacuum chamber. The appeal of APP systems in surface cleaning, however, is reduced by lack of a predictive link among the processing parameters, surface-plasma reactions, and plasma chemistry responsible for efficient removal. Here, we present a comprehensive multiphysics model of surface cleaning using a microwave assisted atmospheric plasma system as an alternative to chemical cleaning of surfaces. This model can quantitatively predict the processing time for the removal of the contaminant species from the surface. The presented model investigates the dependencies of removal rates and the nature of the contaminant species on the processing parameters. We demonstrate these dependencies by using polypropylene as a model hydrocarbon impurity. The complex and cooperative effects of microwave power, gas flow rate, torch-substrate distance, and tilt angle have been explored for understanding factors behind efficient cleaning. Our results show that the rate of hydrocarbon degradation is highly dependent on gas temperatures over the surface, flow pattern, and torch-substrate distance and depends less on the angle of attack. This study helps to optimize the values for operational parameters of atmospheric plasma processing that speeds up the experiments toward achieving a higher surface cleaning rate.

Understanding the depletion of electrons in dusty plasmas at atmospheric pressure

The nucleation and growth of NPs in the gas phase using atmospheric-pressure plasma systems is an important approach to synthesizing novel dimensionally-controlled materials. Here, we investigated the effect of the NPs on a typical type of continuous-flow, substrate-free plasma at atmospheric pressure to understand their potential contribution to electron density changes. A tandem plasma system was set up consisting of one plasma reactor that produced carbonaceous NPs from mixtures of argon and hexane, and another identical plasma reactor where the as-grown particles were injected and non-intrusive electrical and optical measurements were performed. The electron densities obtained from conductivity measurements and a plasma fluid model were found to decrease in the presence of NPs. However, control experiments revealed that the main source of the electron depletion was residual vapor or reaction byproducts in the form of molecular species or nanoclusters and not the particles themselves. These results were validated by constant number Monte Carlo simulations which showed that at the experimentally-measured conditions, the NPs were not of sufficiently high enough concentration to reduce the electron density; however, if molecules or clusters are ionizable, they remain in sufficient concentration to deplete electron densities. Our study shows that at atmospheric pressure, because of their typically larger electron density values, particle-producing plasmas are distinct from those at low pressure, and nanoparticle formation does not have the same impact while molecular-scale species may be a more important consideration.

Correlation between gas-phase OH density and intensity of luminol chemiluminescence in liquid interacting with atmospheric-pressure plasma

The relationship between the density of OH radicals in the gas phase and the intensity of luminol chemiluminescence was investigated using an atmospheric-pressure plasma system in contact with liquid. A thin luminol chemiluminescence was observed just below the plasma–liquid interface when the plasma was generated on the aqueous solution surface with luminol. The radial region with the chemiluminescence was approximately 2.6 times larger than that of the plasma with the optical emission, and was similar to the diameter of the region with OH radicals in the gas phase. The decay time constant of the intensity of the luminol chemiluminescence in the afterglow phase of the pulsed discharge was approximately 100 s, while the optical emission intensity at the second positive system of molecular nitrogen decayed immediately after the termination of the discharge current. On the other hand, the decay time constant of the OH radical density was approximately 100 s in the afterglow phase. These experimental results indicate that the luminol chemiluminescence is induced by the transport of OH radicals to the plasma–liquid interface. It is considered that the chemiluminescence originates from the reaction with O which is produced by .

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.

FTIR study of the surface properties and tribological behaviors of plasma-modified UHMWPE and zirconia

Zirconia and ultra-high molecular weight polyethylene (UHMWPE) are common materials for artificial joints. However, the failure of artificial joints is mainly caused by the wear of UHMWPE. Therefore, the development of effective measures to enhance the service life of UHMWPE is one of the most important facets of research on total joint replacement. The purpose of this study is to use an atmospheric-pressure plasma system to modify zirconia and UHMPWE surfaces, which is expected to increase the adsorption of joint-lubricating fluids, thus reducing the abrasion and wear of UHMWPE (73% improvement). Surface modification experiments were carried out using an atmospheric-pressure plasma system, while fourier transform infrared spectroscopy was used to characterize the surfaces treated with atmospheric-pressure plasma. The results of water contact angle tests indicated that the plasma-treated material surfaces exhibited excellent hydrophilicity (70% improvement). In addition, the treatment of materials with atmospheric plasma was confirmed to increase the adsorption of lubricating fluid and reduce wear, thus extending the service life of UHMWPE.

Methods of improving spatial resolution for IR spectroscopy in atmospheric-pressure plasma systems

High-temperature, atmospheric pressure plasma systems operated in molecular gases present complex diagnostic challenges. Infrared spectroscopy has been used to make measurements of the absorbance spectrum of complex molecular gas mixtures and thereby calculate the concentrations and species temperatures in these systems. For atmospheric-pressure systems, high spatial gradients arise and high spatial-resolution measurements are thus desirable. Some systems have achieved increased spatial resolution by reducing the beam diameter. However, this increase in spatial resolution comes at the expense of the optical throughput. Here we propose modifying a commercial Fourier Transform, Infrared spectrometer system with a set of simple optical elements. This design allows for scannable, high spatial resolution absorbance spectrum measurements of a complex molecular gas mix. We analyze the signal-to-noise ratio for this design and compare it with the diameter reduction method. For sufficiently low plasma radiation levels, this design improves the signal-to-noise ratio relative to reducing the beam diameter size while transmitting nearly all of the beam power. However, whether this design can achieve the desired sub-mm spatial resolution depends on the radiating area of the infrared light source in the spectrometer.

Development of non-thermal atmospheric pressure plasma system for surface modification of polymeric materials

Non-thermal plasma has become one of the new technologies which are highly developed now days. This happens because the cold plasma using the principle of generated reactive gases that have the ability to modify the surface properties of a material or product without changing the original characteristics of the material. The purpose of this study is to develop a cold plasma system that operates at atmospheric pressure and investigates the effect of cold plasma treatment to change the surface characteristics of the polymer material polyethylene (PE) at various time conditions. We are successfully developing a non-thermal plasma system that can operate at atmospheric pressure and can be run with Helium or Argon gas. The characteristics of plasma will be discussed from the view of its electrical property, plasma discharge regime andoperation temperature. Experiment results on plasma treatment on PE material shows the changes of surface properties of originally hydrophobic material PE becomes hydrophilic by only few seconds of plasma treatment and level of hydrophilicity become greater with increasing duration of plasma treatment. Confirmation of this is shown by the measurement of contact angle of droplets of water on the surface of PE are getting smaller.

Process conditions for complete decomposition of CHF3 in a dielectric barrier discharge reactor

Plasma decomposition of CHF3 was investigated using a dielectric barrier discharge immersed in an electrically insulating oil bath in a mixture of CHF3, O2, and N2. CHF3 was well decomposed under a relatively high applied voltage in an atmospheric pressure plasma system. The main by-product was CO2 and its selectivity increased with a decrease in the CHF3 concentration in the feed. Complete decomposition of CHF3 was achieved at a typical process range: an applied voltage ≥7.0 kVp, an initial CHF3 flow rate of 3ml/min, and a total flow rate of 500ml/min. The value of energy efficiency and energy density at the center range for the complete decomposition of CHF3 was 0.01 mmol/kJ and 6.00kWh/Nm3, respectively.

Roughening of Polyimide Surface for Inkjet Printing by Plasma Etching Using the Polyimide Masked with Polystyrene Nanosphere Array.

Two key conditions are required for the application of fine-line inkjet printing onto a flexible substrate such as polyimide (PI): linewidth control during the inkjetting process, and a strong adhesion of the polyimide surface to the ink after the ink solidifies. In this study, the properties of a polyimide surface that was roughened through etching in a He/SF6 plasma, using a polystyrene nanosphere array as the etch mask, were investigated. The near-atmospheric-pressure plasma system of the He/SF6 plasma that was used exhibits two notable properties in this context: similar to an atmospheric-pressure plasma system, it can easily handle inline substrate processing; and, similar to a vacuum system, it can control the process gas environment. Through the use of plasma etching, the polyimide surface masked the 120-nm-diameter polystyrene nanospheres, thereby forming a roughened nanoscale polyimide surface. This surface exhibited not only a greater hydrophobicity--with a contact angle of about 150° for water and about 30° for silver ink, indicating better silver linewidth control during the silver inkjetting process--but also a stronger adhesion to the silver ink sprayed onto it when compared with the flat polyimide surface.

Atmospheric pressure plasma chemical vapor deposition reactor for 100 mm wafers, optimized for minimum contamination at low gas flow rates

Gas discharge plasmas used for thinfilm deposition by plasma-enhanced chemical vapor deposition (PECVD) must be devoid of contaminants, like dust or active species which disturb the intended chemical reaction. In atmospheric pressure plasma systems employing an inert gas, the main source of such contamination is the residual air inside the system. To enable the construction of an atmospheric pressure plasma (APP) system with minimal contamination, we have carried out fluid dynamic simulation of the APP chamber into which an inert gas is injected at different mass flow rates. On the basis of the simulation results, we have designed and built a simple, scaled APP system, which is capable of holding a 100 mm substrate wafer, so that the presence of air (contamination) in the APP chamber is minimized with as low a flow rate of argon as possible. This is examined systematically by examining optical emission from the plasma as a function of inert gas flow rate. It is found that optical emission from the plasma shows the presence of atmospheric air, if the inlet argon flow rate is lowered below 300 sccm. That there is minimal contamination of the APP reactor built here, was verified by conducting an atmospheric pressure PECVD process under acetylene flow, combined with argon flow at 100 sccm and 500 sccm. The deposition of a polymer coating is confirmed by infrared spectroscopy. X-ray photoelectron spectroscopy shows that the polymer coating contains only 5% of oxygen, which is comparable to the oxygen content in polymer deposits obtained in low-pressure PECVD systems.

Antimicrobial nano-silver non-woven polyethylene terephthalate fabric via an atmospheric pressure plasma deposition process

An antimicrobial nano-silver non-woven polyethylene terephthalate (PET) fabric has been prepared in a three step process. The fabrics were first pretreated by depositing a layer of organosilicon thin film using an atmospheric pressure plasma system, then silver nano-particles (AgNPs) were incorporated into the fabrics by a dipping-dry process, and finally the nano-particles were covered by a second organosilicon layer of 10-50 nm, which acts as a barrier layer. Different surface characterization techniques like SEM and XPS have been implemented to study the morphology and the chemical composition of the nano-silver fabrics. Based on these techniques, a uniform immobilization of AgNPs in the PET matrix has been observed. The antimicrobial activity of the treated fabrics has also been tested using P. aeruginosa, S. aureus and C. albicans. It reveals that the thickness of the barrier layer has a strong effect on the bacterial reduction of the fabrics. The durability and stability of the AgNPs on the fabrics has also been investigated in a washing process. By doing so, it is confirmed that the barrier layer can effectively prevent the release of AgNPs and that the thickness of the barrier layer is an important parameter to control the silver ions release.

Antibacterial activity of nano-silver non-woven fabric prepared by atmospheric pressure plasma deposition

Antimicrobial non-woven polyethylene terephthalate (PET) fabric containing nano-silver of different concentrations has been prepared in a novel three step process. Nano-silver has been incorporated in between two layers of organosilicon thin film deposited by an atmospheric pressure plasma system. The top layer of 10nm thickness was used as a barrier to prevent release of nanoparticles from the surface. The antimicrobial activity of the nano-silver fabrics was tested using Staphylococcus aureus and Escherichia coli by a dilution method. The effect of silver concentration on the lag phase, the specific cell growth rate, and the cell concentration has been studied and discussed based on bacterial growth curves.