Showing papers in "Plasma Processes and Polymers in 2012"

Atmospheric Pressure Low Temperature Direct Plasma Technology: Status and Challenges for Thin Film Deposition

Abstract: Over the last ten years, expansion of atmospheric pressure plasma solutions for surface treatment of materials has been remarkable, however direct plasma technology for thin film deposition needs still great effort. The objective of this paper is to establish the state of the art on scientific and technologic locks, which have to be opened to consider direct atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) a viable option for industrial application. Basic scientific principles to understand and optimize an AP-PECVD process are summarized. Laboratory reactor configurations are reviewed. Reference points for the design and use of AP-PECVD reactors according to the desired thin film properties are given. Finally, solutions to avoid powder formation and to increase the thin film growth rate are discussed.

Plasma–Liquid Interactions at Atmospheric Pressure for Nanomaterials Synthesis and Surface Engineering

Abstract: Plasma-induced non-equilibrium liquid chemistry (PiLC) offers enhanced opportunities over solution chemistry for developing new nanomaterials and tailoring their functional properties. Recent advances in the design and scientific understanding of microplasma devices operating at atmospheric pressure offer simple and effective routes to non-equilibrium chemistry for both scientific study and future nanomanufacturing. This paper presents a short review of our recent work on atmospheric pressure plasma–liquid interactions used in the fabrication and functionalization of nanoparticles. A brief discussion of possible electron-liquid reactions highlights outstanding scientific and engineering questions.

Plasma‐Induced Death of HepG2 Cancer Cells: Intracellular Effects of Reactive Species

Abstract: Reports show that cold atmospheric-pressure plasmas can induce death of cancer cells in several minutes. However, very little is presently known about the mechanism of the plasma-induced death of cancer cells. In this paper, an atmospheric-pressure plasma plume is used to treat HepG2 cells. The experimental results show that the plasma can effectively control the intracellular concentrations of ROS, NO and lipid peroxide. It is shown that these concentrations are directly related to the mechanism of the HepG2 death, which involves several stages. First, the plasma generates NO species, which increases the NO concentration in the extracellular medium. Second, the intracellular NO concentration is increased due to the NO diffusion from the medium. Third, an increase in the intracellular NO concentration leads to the increase of the intracellular ROS concentration. Fourth, the increased oxidative stress results in more effective lipid peroxidation and consequently, cell injury. The combined action of NO, ROS and lipid peroxide species eventually results in the HepG2 cell death. The mechanism of death of human hepatocellular carcinoma cells (HepG2) induced by atmospheric-pressure room-temperature plasma, related to the plasma-controlled intracellular concentrations of reactive oxygen species (ROS), nitric oxide (NO) and lipid peroxide is revealed. Only 34.75 s are required to reduce the number of the viable HepG2 cells by 50%.

Protein Inactivation by Low-temperature Atmospheric Pressure Plasma in Aqueous Solution

Abstract: Plasma medicine is an attractive new research area, but fundamental information related to plasma modification of biomacromolecules in aqueous solution remains elusive. As described herein, we investigated the chemical effects of low-temperature atmospheric pressure plasma on protein in aqueous solution using lysozyme as a model. Plasma treatment decreased enzymatic activity and changed the secondary structure that results from the increased molecular weight of lysozyme with chemical modification. These effects arise neither from UV light nor from plasma heat, suggesting that the reactive species generated by the plasma affect lysozyme. The information presented in this paper represents a crucial first step for elucidating chemical reactions induced by plasma on proteins for biomedical applications.

Reactive Oxygen Species in a Non-thermal Plasma Microjet and Water System: Generation, Conversion, and Contributions to Bacteria Inactivation—An Analysis by Electron Spin Resonance Spectroscopy†

Abstract: Hydroxyl radical (•OH) and singlet oxygen (1O2) were detected by electron spin resonance (ESR) spectroscopy in a direct current He/O2 (2%) non-thermal plasma microjet-water system. is shown to be the precursor of •OH. The concentrations of 1O2 and •OH are evaluated to be around 6 × 10−4 and 1.2 × 10−5 M, respectively. The survival rates of S. aureus exposed to plasma for 20 s in 1 ml H2O, SOD (100 U, for scavenging ), D-Man (0.15 M, for scavenging •OH), and L-His (0.15 M, for scavenging •OH and 1O2) solutions were 0.7, 1.6, 13.4, and 40.9%, respectively, indicating that 1O2 contributes the most to the inactivation.

Effects of Reactor Packing Materials on H2 Production by CO2 Reforming of CH4 in a Dielectric Barrier Discharge

Abstract: Non-thermal plasma has been investigated for CO2 reforming of CH4 in a coaxial DBD reactor with different reactor packing materials placed into the discharge gap. Both the chemical and physical effects on reaction performance have been examined for the addition of quartz wool, ?-Al2O3 and zeolite 3A, in order to gain a better understanding of plasma interactions with materials during CH4 reforming reactions. Quartz wool was found to enhance the conversion of CH4 and improve H2 yields as a result of changes in the physical properties of the discharge; electrical measurements showed an increase in the intensity of microdischarge filaments over quartz wool. In the presence of Al2O3 and zeolite 3A, the discharge intensity was reduced and consequently CH4 and CO2 conversions were lower for these materials. However, in the presence of zeolite 3A improved selectivities towards H2 and light hydrocarbons acetylene/ethylene were obtained and formation of liquid hydrocarbons was inhibited due to shape-selectivity determined by the zeolite pore size.

In Vitro Susceptibility of Important Skin and Wound Pathogens Against Low Temperature Atmospheric Pressure Plasma Jet (APPJ) and Dielectric Barrier Discharge Plasma (DBD)

Abstract: Plasma medicine has become an emerging field in medical sciences since cold plasma has demonstrated important antimicrobial properties. As microbial plasma susceptibility data yet are not available, the susceptibility of 194 wound isolates exhibiting multiple antibiotic resistance was tested in vitro to CP and correlated with inhibition zones. Inhibition zones increased in parallel with the number of antibiotic classes to which the tested strain exhibit resistance. CP exhibited strong antimicrobial efficacy against most important clinical skin and wound pathogens in vitro irrespective of multidrug resistance.

Inactivation of Bacillus subtilis Spores in Water by a Direct‐Current, Cold Atmospheric‐Pressure Air Plasma Microjet

Abstract: P. Sun, H. Wu, J. Zhang, J. FangCollege of Engineering, Peking University, Beijing, ChinaE-mail: zhangjue@pku.edu.cnN. Bai, H. Zhou, R. Wang, H. Feng, J. Zhang, J. FangAcademy for Advanced Interdisciplinary Studies, PekingUniversity, Beijing, ChinaN. Bai, H. ZhouWest China College of Stomatology, Sichuan University,Chengdu, ChinaW. ZhuDepartment of Applied Science and Technology, Saint Peter’sCollege, New Jersey, USAE-mail: wzhu@spc.eduPeng Sun and Haiyan Wu contributed equally to this work.

Decontamination of Microbiologically Contaminated Specimen by Direct and Indirect Plasma Treatment

Abstract: Gentle sanitation of fresh fruits and vegetables is highly demanded. Currently used methods lead to losses in product amounts and quality. Furthermore, these methods go along with high costs and chemical residues. One reason for such problems is microbial contamination. Due to the fact that conventional decontamination processes are not suitable for preservation of fresh produce, alternatives such as plasma technology can be helpful. Three different artificial specimen and seeds of Brassica napus were contaminated with endospores of Bacillus atrophaeus and afterwards plasma treated directly with DBD plasma and indirectly with microwave plasma processed air. After a treatment time of 15 minutes reduction rates between 0.5 and 5.2 log were achieved. The viability of seeds was not affected. The advantages of plasma and promising results offer a wide range of possible uses in food industry.

Plasma Polymerization of Acrylic Acid by Atmospheric Pressure Nitrogen Plasma Jet for Biomedical Applications

Abstract: Polyacrylic acid thin films have been deposited by an original and fast technique to grow organic coatings: a pulsed-arc atmospheric pressure plasma jet. Liquid acrylic acid was introduced in the nitrogen plasma jet and OES was used to measure the fragmentation of the precursor. The films were characterized by XPS, FTIR and SEM analyses before and after soaking in water. The water stability was also investigated by weight loss measurement. A high retention of carboxylic moieties, i.e. functional groups of the monomer has been observed for coatings deposited under mild conditions for the jet (low frequency and high jet speed). These films have been used for cell adhesion using human ovarian carcinoma cells (NIH:OVCAR-3). Good results have been obtained depending on the plasma parameters, showing that atmospheric pressure plasma jet is a promising technique to grow organic thin films for biomedical applications.

The Role of Albumin and Fibronectin in the Adhesion of Fibroblasts to Plasma Polymer Surfaces

Abstract: Plasma polymer coatings are widely applied to the modification of biomaterial surfaces. In order to understand the role of the surface in the adhesion of cells to these materials, it is necessary to understand how protein adsorption is influenced by the plasma polymer surface chemistry. In coated scaffolds, plasma polymerised allylamine has been found to encourage fibroblast adhesion while plasma polymerised hexane reduces cell adhesion. To study the role of proteins in this process, albumin and fibronectin are pre-adsorbed individually, competitively or sequentially to the plasma polymer surfaces before seeding them with a culture of 3T3 fibroblasts. Significant dependence upon the protein pre-adsorption was seen in the adhered cell numbers. In situ measurements of protein adsorption using a quartz crystal microbalance help to elucidate the factors that govern the observed cellular response. The measured protein adsorption is rationalised in terms of our knowledge of the surface chemistry of these plasma polymers. We found that high cell adhesion is related to the ability of fibronectin to displace albumin. This ability is reduced on the hydrophobic plasma polymer as well as by adsorbing albumin and fibronectin sequentially.

The Role of VUV Radiation in the Inactivation of Bacteria with an Atmospheric Pressure Plasma Jet

Abstract: A modified version of a micro scale atmospheric pressure plasma jet (\mu-APPJ) source, so-called X-Jet, is used to study the role of plasma generated VUV photons in the inactivation of E coli bacteria The plasma is operated in He gas or a He/O2 mixture and the X-Jet modification of the jet geometry allows effective separation of heavy reactive particles (such as O atoms or ozone molecules) from the plasma-generated photons The measurements of the evolution of zone of inhibitions formed in monolayers of vegetative E coli bacteria, of VUV emission intensity and of positive ion spectra show that photochemistry in the gas phase followed by photochemistry products impacting on bacteria can result in bacterial inactivation Interestingly, this process is more effective than direct inactivation by VUV radiation damage Mainly protonated water cluster ions are detected by mass spectrometry indicating that water impurity has to be carefully considered The measurements indicate that the combination of the presence of water cluster ions and O2 molecules at the surface leads to the strongest effect Additionally, it seem that the interaction of VUV photons with effluent of He/O2 plasma leads to enhanced formation of O3, which is not the case when only O2 molecules and gas impurities at room temperature interacts with plasma generated VUV photons

An Investigation into the Dominant Reactions for Ethylene Destruction in Non‐Thermal Atmospheric Plasmas

Abstract: A crucial step, which is still not well understood in the destruction of volatile org. compds. (VOCs) with low temp. plasmas, is the initiation of the process. Here, we present a kinetic model for the destruction of ethylene in low temp. plasmas that allows us to calc. the relative importance of all plasma species and their related reactions. Modifying the ethylene concn. and/or the SED had a major impact on the relative importance of the radicals (i.e., mainly at. oxygen) and the metastable nitrogen (i.e., more specifically N2(A3?u+)) in the destruction process. Our results show that the direct destruction by electron impact reactions for ethylene can be neglected; however, we can certainly not neglect the influence of N2(A3?u+)). [on SciFinder(R)]

Deposition of Hydrophobic Functional Groups on Wood Surfaces Using Atmospheric-Pressure Dielectric Barrier Discharge in Helium- Hexamethyldisiloxane Gas Mixtures

Abstract: O. Levasseur, Prof. L. Stafford Departement de Physique, Universite de Montreal, Montreal (Quebec) H3C 3J7, Canada E-mail: luc.stafford@umontreal.ca N. Gherardi, N. Naude Universite de Toulouse, UPS, INPT, LAPLACE, F-31062 Toulouse Cedex 9, France N. Gherardi, N. Naude CNRS, LAPLACE, F-31062 Toulouse Cedex 9, France V. Blanchard, P. Blanchet FPInnovations – Division des Produits du Bois, Quebec (Quebec) G1P 4R4, Canada B. Riedl Centre de Recherche sur le Bois, Universite Laval, Quebec (Quebec) G1K 7P4, Canada A. Sarkissian Plasmionique, Varennes (Quebec) J3X 1S2, Canada This work examines the functionalization of sugar maple (Acer saccharum) and black spruce (Picea mariana) wood surfaces using an atmospheric-pressure dielectric barrier discharge in He and He/HMDSO (hexamethyldisiloxane) gas mixtures. Wood samples were placed on one of the electrodes and the plasma was sustained by applying a 3.5 kV peak-to-peak voltage at 12 kHz. Analysis of the discharge stability through current–voltage (I–V) characteristics revealed a filamentary behaviour, in sharp contrast with the homogeneous He discharge obtained with a glass sample. Optical emission spectroscopy performed near the wood vicinity revealed strong N2 and N þ 2 emissions, suggesting that wood outgassing plays an important role in the evolution of the discharge regime. Analysis of the surface wettability through water contact angle (WCA) measurements indicated that freshly sanded wood samples treated in He/HMDSO plasmas became more hydrophobic with WCAs in the 1208–1408 range depending on treatment time and wood species. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy measurements on samples exposed to He/HMDSO plasmas revealed the deposition of hydrophobic Si(CH3)3-O-Si(CH3)2, Si(CH3)3 and Si(CH3)2 functional groups as well as an increase of the CH-to-OH band intensity ratio. For relatively thick coatings, the WCA following natural aging under uncontrolled conditions remained constant at 1328 38 which highlights the stability of the plasma-deposited thin films, a very promising result for structural and decorative outdoor applications.

Hierarchical, Plasma Nanotextured, Robust Superamphiphobic Polymeric Surfaces Structurally Stabilized Through a Wetting–drying Cycle

Abstract: Plasma etched and simultaneously randomly roughened (nanotextured) polymethylmethacrylate (PMMA) substrates show hierarchical roughness and complex high-aspect-ratio morphology. Here, they are investigated as superamphiphobic surfaces, after plasma deposition of a thin fluorocarbon film. Inspired by the need to allow their “real world” use, we explore two major stability issues of such superamphiphobic surfaces: (i) the structural stability of the nanotexture against capillary and adhesion forces during successive wetting–drying cycles, and (ii) the thermodynamic stability (robustness) of these surfaces related to the maximum sustainable pressure of the Cassie–Baxter inhomogeneous wetting state. We show that surfaces etched in oxygen plasma up to 4 min (with texture height ≈600 nm) are stable against successive wetting–drying cycles, while surfaces treated for longer time show highly porous nanofibrous morphology which is coalesced and stabilized upon wetting, allowing their potential long-term use. Robust superhydrophobic and superoleophobic behavior is observed in drop compression tests with water (on 2, 4, 10 min plasma etched surfaces) and diiodomethane (on 4 and 10 min plasma etched surfaces), respectively, and no wetting transition is observed for these two liquids even at maximum drop compression possible (1.5 kPa). Robust oleophobic behavior with sticky surfaces is observed for 1 and 2 min etching and with diiodomethane without transition to wetted states even upon maximum compression. On the contrary, wetting transition is observed for soya oil upon repeated compression.

Plasma Functionalization of Multiwalled Carbon Nanotubes and Their Use in the Preparation of Nylon 6-Based Nanohybrids

Abstract: The possibility to obtain carbon nanotubes (CNT)/polyamide 6 composites with excellent mechanical properties in a simple, industrially scalable way is investigated. Commercial CNTs are treated by plasma while changing some key parameters (exposure time, plasma power, type of gas) in order to optimize the process and to achieve a sufficient degree of functionalization. The treated samples are characterized by Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The most interesting samples are selected to be used as reinforcing fillers, in different concentrations, in a polyamide 6 matrix. The mechanical tests show a dramatic increase of both tensile and impact properties, due to the achievement of a good wettability, and an efficient dispersion of the CNTs in the polymer matrix, as confirmed by scanning electron microscopy observations.

DNA Damage in Mammalian Cells by Non-thermal Atmospheric Pressure Microsecond Pulsed Dielectric Barrier Discharge Plasma is not Mediated by Ozone

Abstract: Non-thermal dielectric barrier discharge (DBD) plasma is now being widely developed for various clinical applications1,2 but the mechanisms of interaction of such plasmas with mammalian cells are still not well understood. It is known that DBD plasma produces ozone and it is possible that the effects of plasma may be mediated purely by ozone. Although typically requiring much higher treatment time than the typical plasma treatment times reported here, ozonation is, in fact, widely employed to kill microorganisms in water and is also used for wound healing. It has been shown earlier that plasma treatment of mammalian cells submerged in a shallow layer of culture medium can result in dose dependent DNA damage. We wanted to understand the role of ozone in mediating the interaction of non-thermal plasma DBD plasma with mammalian cells. Upon comparing plasma treatment of mammalian breast epithelial cells with ozone treatment we found that ozone treatment is qualitatively different from non-thermal DBD plasma and in fact does not play a role in mediating the observed effects of plasma on mammalian cells.

Atmospheric Pressure Pulsed Plasma Copolymerisation of Maleic Anhydride and Vinyltrimethoxysilane: Influence of Electrical Parameters on Chemistry, Morphology and Deposition Rate of the Coatings

Abstract: Tuning of the electrical parameter (e.g. power and pulsed discharge) of an Atmospheric Pressure Dielectric Barrier Discharge (AP-DBD) plasma of Maleic Anhydride (MA) and vinyltrimethoxysilane (VTMOS) allows the formation of coatings with different combination of anhydride/carboxylic group surface density, morphology and deposition rate. Pulsing of the discharge favours the incorporation of MA with a high structural retention, leading to coatings with a chemical composition similar to the expected conventional MA-VTMOS copolymer one. A kinetic model based on the free radical polymerisation is developed to correlate the carboxylic groups density on the plasma functionalised surface and the duration of the plasma off-time.

The Role of Oxygen and Surface Reactions in the Deposition of Silicon Oxide like Films from HMDSO at Atmospheric Pressure

Abstract: The deposition of thin SiO2-like films by means of atmospheric pressure microplasma jets with admixture of hexamethyldisiloxane (HMDSO) and oxygen and the role of surface reactions in film growth are investigated. Two types of microplasma jets, one with a planar electrodes and operated in helium gas and the other one with a coaxial geometry operated in argon, are used to study the deposition process. The growth rate of the film and the carbon-content in the film are measured as a function of the O2 and HMDSO admixture in the planar jet and are compared to mass spectrometry measurements of the consumption of HMDSO. Additionally, the localized nature of the jet–substrate interaction is utilized to study surface reactions by applying two jets on a rotating substrate. The addition of oxygen into the gas mixture increases HMDSO depletion and the growth rate and results in the deposition of carbon free films. The surface reaction is responsible for the carbon removal from the growing film. Moreover, carbon free films can be deposited even without addition of oxygen, when coaxial jet operated with argon is used for the surface treatment. We hypothesize that ions or excited species (metastables) could be responsible for the observed effect.

Retraction: Plasma Acid: Water Treated by Dielectric Barrier Discharge

Abstract: It is demonstrated that direct exposure of deionized water to a dielectric barrier discharge (DBD) plasma creates an acid (pH 2) and is in fact, a strong oxidizer (providing, e.g., peroxidation of a cell membrane). This study addresses the question: which acid is created in water by plasma treatment. Two major possibilities are considered: nitric/nitrous acid and an acid which consist of a hydrogen cation (Hþ) and a superoxide anion (O 2 ), which, for the lack of a better term, we call plasma acid. The presence of nitric/nitrous acid in the water after plasma treatment in air is confirmed, although the observed pH 2 cannot be completely explained by the production of nitric acid. Moreover, experiments with oxygen-plasma treatment of water also lead to high acidity, without production of nitrogen based acids at all. Therefore, O 2 , the conjugate base of the plasma acid, is at least partially responsible for both lowering of the pH and the increase in the oxidizing power of the solution. Experiments indicate that peroxides such as H2O2 and O 2 , together with an acidic environment are likely to be responsible for the oxidation properties of the plasma treated water. This plasma acid remains stable for at least a day, depending on the gas where plasma is generated, but the effect is temporal. Existence of a temporal and stable oxidizer created using the plasma treatment of pure water not only raises interesting scientific questions and possibilities, but is also likely to provide many applications in situations where direct plasma treatment may be difficult to achieve. 0 5 10 15 20 25 30 35 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5

Plasma Sterilization of Pharmaceutical Products: From Basics to Production

Abstract: For the first time, a commercial low pressure plasma sterilization system integrated in a pharmaceutical filling line is presented. The route from a laboratory plasma reactor to an industry scale plasma sterilization reactor is shown. Absolutely calibrated measurements (e.g. OES and Langmuir probe) yield to a knowledge transfer from an experimental set-up to an industrial reactor. Spore count reduction of 4 log in 10 s of Geobacillus stearothermophilus and Bacillus subtilis spores prove the applicability of an industrial grade plasma sterilization reactor for transfer isolators typically used in pharmaceutical filling and packaging lines.

Atmospheric Pressure Plasma Surface Modification of Poly(D,L-lactic acid) Increases Fibroblast, Osteoblast and Keratinocyte Adhesion and Proliferation

Abstract: An atmospheric pressure plasma deposition for P(d,L)LA (PLA) film was used to modify polymer surface properties using 1,2-diaminopropane and acrylic acid as precursors. These two different plasma coatings result in a high density of amino groups (PLA-NH2) and carboxylic groups (PLACOOH) onto PLA surface as demonstrated by Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Plasma coatings modified PLA surface wettability and proteins adsorption from fetal bovine serum (FBS), influencing cell adhesion and proliferation of 3T3 mouse fibroblast, MC-3T3 E1mouse pre-osteoblast, and HaCaT cells (human keratinocytes). In particular both coatings increased pre-osteoblast and keratinocyte adhesion while no effect was observed on fibroblast. Moreover, cell proliferation assessed after 48h by Tox-8 assay was significantly higher for osteoblast cells and keratinocyte seeded onto both PLA-NH2 and PLACOOH compared to cells seeded onto normal PLA. On the basis of the obtained data, the atmospheric pressure plasma deposition described might represent an innovative and useful tool for bone and skin tissue engineering.

Cold Atmospheric Plasma for Surface Disinfection

Abstract: A new design evolved from the surface microdischarge electrode system has been developed for the application of surface disinfection. Having the electrode encapsulated in a dielectric surface the plasma is produced directly on the surface of the electrode which therefore becomes disinfected. Experiments with bacteria were carried out and results show that the surface can be disinfected within 30s with typical operating conditions. Even sterilization appears possible in a reasonable time. Possible applications of this electrode design are discussed for regular disinfection of work surfaces, laboratory benches, etc.