Radio Frequency Air Plasma Research Articles

Fucoidan- and Ciprofloxacin-Doped Plasma-Activated Polymer Coatings on Biodegradable Zinc: Hemocompatibility and Drug Release.

Blood-contacting medical devices such as biodegradable metallic bone implant materials are expected to show excellent hemocompatibility both in vitro and in vivo. Different approaches are being studied and used to modify biomaterial surfaces for enhanced biocompatibility and hemocompatibility. However, the composition of degradable biomaterial must address several drawbacks at once. Iron-reinforced zinc material was used as a metallic substrate with improved mechanical properties when compared with those of pure zinc. Poly(lactic) acid (PLA) or polyethylenimine (PEI) was selected as a polymeric matrix for further doping with antibiotic ciprofloxacin (CPR) and marine-sourced polysaccharide fucoidan (FU), which are known for their antibacterial and potential anticoagulant properties, respectively. Radiofrequency air plasma was employed to induce metallic/polymer-coated surface activation before further modification with FU/CPR. Sample surface morphology and composition were studied and evaluated (contact angle measurements, AFM, SEM, and FT-IR) along with the hemolysis ratio and platelet adhesion test. Successful doping of the polymer layer by FU/CRP was confirmed. While PEI induced severe hemolysis over 12%, the PLA-coated samples exhibited even lower hemolysis (∼2%) than uncoated samples while the uncoated samples showed the lowest platelet adhesion. Moreover, gradual antibiotic release from PLA determined by the electrochemical methods using screen-printed carbon electrodes was observed after 24, 48, and 72 h, making the PLA-coated zinc-based material an attractive candidate for biodegradable material design.

Effect of low-pressure radio-frequency air plasma on chitosan films

The effect of low-frequency (15 kHz), low-pressure (10 Pa) air plasma treatment on freshly prepared chitosan films at processing times from 3 to 10 min has been explored. The films were prepared using chitosan solutions in dilute acetic acid. The influence of the plasma exposure time on the composition, morphology, and hydrophilic properties of the film surfaces is discussed.

Generation of highly porous silver nanowire networks by plasma treatment and their direct application as supercapacitor electrodes.

Exposure to plasma can significantly increase the surface area of silver species and their resistance to oxidation. While some work investigating plasma-treated silver has been done, limited morphologies and applications have been explored. We hereby explore this effect on silver nanowires (AgNWs) through medium-vacuum air plasma exposure time ranging between 30 s to 60 min. These plasma-treated AgNW networks are directly applied as supercapacitor electrodes, without any carbon or polymer additives that are typically employed alongside silver in energy storage applications. The plasma treatment consequently affected the electrochemical performance of AgNWs, where longer treatment times resulted in higher energy storage capacity. An increase in resistance was observed for plasma treatment times greater than or equal to 5 min, due to the switch from the percolation threshold of the metallic Ag phase to the Ag2O phase. Despite an initial drop in stored energy, an overall improvement in energy storage capacity was observed throughout cycling, where the optimal plasma treatment time of 5 min resulted in an increase of 320% of its starting value with near 100% coulombic efficiency, through the development of stable redox-active surface nanostructures.

Patterning of silver on the micro- and nano-scale by local oxidation using air plasma

A novel low temperature micro- and nano-patterning approach of metal silver thin films is demonstrated. The process involves local deposition of carbon mask created in situ using the e-beam of scanning electron microscope followed by radio frequency air plasma oxidation. We show that by selecting the appropriate experimental conditions, silver can be transformed locally from metallic to nanoporous oxide. Etching the oxide phase in ammonia solution allows obtaining metal silver patterns. We further show that this approach is not limited to thin films but can be rather extended to nanowires which allows creating periodic metal/metal oxide nanojunctions.

Quantification and physics of cold plasma treatment of organic liquid surfaces

Plasma treatment increases the surface energy of condensed phases: solids and liquids. Two independent methods of the quantification of the influence imposed by a cold radiofrequency air plasma treatment on the surface properties of silicone oils (polydimethylsiloxane) of various molecular masses and castor oil are introduced. Under the first method the water droplet coated by oils was exposed to the cold air radiofrequency plasma, resulting in an increase of oil/air surface energy. An expression relating the oil/air surface energy to the apparent contact angle of the water droplet coated with oil was derived. The apparent contact angle was established experimentally. Calculation of the oil/air surface energy and spreading parameter was carried out for the various plasma-treated silicone and castor oils. The second method is based on the measurement of the electret response of the plasma-treated liquids.

Modification of starch using low pressure radio frequency air plasma

Cold plasma is one of the emerging nonthermal food processing technologies recently drawn interest as a chemical-free biopolymer modification method. In the present study, two starches (corn and tapioca) were exposed to low pressure radio frequency plasma at 40 W and 60 W for 10 and 20 min. The effect of air plasma treatment on the starch properties was determined by measuring amylose content, swelling power, powder flowability properties, gelatinization temperatures and pasting properties. The amylose content of corn and tapioca starches was observed to decreased and increased respectively. Increase in water binding capacity and swelling power of both starches. The results of pH showed partial oxidation of starches as evident from the decrease in pH. Rapid visco analyzer showed an increase in final viscosities after the plasma treatment. The increase in viscosities is the result of higher amounts of leach out of particles from the starch granules. Plasma treated corn starches exhibited lower peak temperatures and enthalpies whereas it increased in tapioca starches. X-ray diffractogram revealed an A-type pattern of both starches and plasma treatment did not show any significant effect on the crystallanity pattern. Cold plasma offers a unique route for starch modification without affecting its bulk properties.

Kirkendall Effect vs Corrosion of Silver Nanocrystals by Atomic Oxygen: From Solid Metal Silver to Nanoporous Silver Oxide

The corrosion of silver upon exposure to atomic oxygen is a unique effect reported in the 1980s and was highly studied to overcome the fast degradation of space shuttles in low earth orbit. In this work, we explored the conversion mechanisms of nanostructures from solid silver to nanoporous silver oxide upon exposure to radiofrequency air plasma. A broad panel of silver nanostructures with various shapes, sizes, and morphologies were considered to carefully examine the different stages of the oxidation process which evolve according to the considered model-system (e.g., nanosphere, nanowire, nanocube, or nanotriangle). Through a set of time-lapse studies and very specific experiments, we explained the generation of nanoporosity according to a mechanism based on two effects: (i) the high strain in the oxide shell generated as a consequence to the oxidation process and amplified by the bombardment of the material with the energetic species present in the radio frequency air plasma and (ii) the Kirkendall ef...

Modification of Konjac Glucomannan by Reduced-Pressure Radio-Frequency Air Plasma

Abstract The potential of reduced-pressure radio-frequency air plasma (RFAP) in the modification of konjac glucomannan (KGM) was investigated. KGM film was exposed to 100 W RFAP for 50 s, 100 s, 150 s, 200 s, and 250 s, ground, and then subjected to various characterizations. Fourier Transform Infrared Spectroscopy (FTIR) revealed that RFAP treatment increased the content of –OH groups in KGM, with the lowest and highest rise occurring at the exposure durations 150 s and 250 s, respectively. RFAP radiation decreased the solubility of KGM at certain exposure durations, but slightly increased its thermal stability. Exposure to RFAP for 150 s and 250 s increased the hardness of the resultant KGM gel, but decreased the viscosity and elasticity of the KGM solution in a duration-dependent manner. Scanning Electron Microscope (SEM) observation revealed that RFAP treatment led to rougher surfaces and XRD (X-Ray Diffraction) analysis indicated the destroyed crystallinity of KGM. Hence, RFAP has potential application in the modification of KGM.

Creating nanoporosity in silver nanocolumns by direct exposure to radio-frequency air plasma.

Nanoporous materials are of great importance for a broad range of applications including catalysis, optical sensors and water filtration. Although several approaches already exist for the creation of nanoporous materials, the race for the development of versatile methods, more suitable for the nanoelectronics industry, is still ongoing. In this communication we report for the first time on the possibility of generating nanoporosity in silver nanocolumns using a dry approach based on the oxidation of silver by direct exposure to a commercially available radio-frequency air plasma. The silver nanocolumns are created by glancing angle deposition using magnetron sputtering of a silver target in pure argon plasma. We show that upon exposure to the rf air plasma, the nanocolumns transform from solid silver into nanoporous silver oxide. We further show that by tuning the plasma pressure and the exposure duration, the oxidation process can be finely adjusted allowing for precisely controlling the morphology and the nanoporosity of the silver oxide nanocolumns. The generation of porosity within the silver nanocolumns is explained according to a cracking-induced oxidation mechanism based on two repeated events occurring alternately during the oxidation process: (i) oxidation of silver upon exposure to the air plasma and (ii) generation of nanocracks and blisters within the oxide layer due to the high internal stress generated within the material during oxidation.

Interaction of cold radiofrequency plasma with seeds of beans (Phaseolus vulgaris).

The impact of cold radiofrequency air plasma on the wetting properties and water imbibition of beans (Phaseolus vulgaris) was studied. The influence of plasma on wetting of a cotyledon and seed coat (testa) was elucidated. It was established that cold plasma treatment leads to hydrophilization of the cotyledon and tissues constituting the testa when they are separately exposed to plasma. By contrast, when the entire bean is exposed to plasma treatment, only the external surface of the bean is hydrophilized by the cold plasma. Water imbibition by plasma-treated beans was studied. Plasma treatment markedly accelerates the water absorption. The crucial role of a micropyle in the process of water imbibition was established. It was established that the final percentage of germination was almost the same in the cases of plasma-treated, untreated, and vacuum-pumped samples. However, the speed of germination was markedly higher for the plasma-treated samples. The influence of the vacuum pumping involved in the cold plasma treatment on the germination was also clarified.

Physical mechanisms of interaction of cold plasma with polymer surfaces

Physical mechanisms of the interaction of cold plasmas with organic surfaces are discussed. Trapping of plasma ions by the CH2 groups of polymer surfaces resulting in their electrical charging is treated. Polyethylene surfaces were exposed to the cold radiofrequency air plasma for different intervals of time. The change in the wettability of these surfaces was registered. The experimentally established characteristic time scales of the interaction of cold plasma with polymer surfaces are inversely proportional to the concentration of ions. The phenomenological kinetic model of the electrical charging of polymer surfaces by plasmas is introduced and analyzed.

Surface modification of polyelectrolyte multilayers by high radio frequency air plasma treatment

Low-temperature plasma treatments are used to perform surface modification on polymers, aiming to improve the surface properties according to the desired application. In this work, polyelectrolyte multilayers (PEMs), built by layer-by-layer deposition technique, were treated using high frequency low-temperature air plasma. We evaluated the effect of the exposure time (20 and 300s) and its effects on PEMs with two different top layers: alginate and carboxymethylcellulose. Chitosan was used as the cationic polymer to build the LbL films with the oppositely charged anionic polymers, alginate and carboxymethylcellulose. Our results showed that the surface topology, wettability and free charges within layers are highly correlated to the polymer pair used. PEMs of the chitosan/alginate system are thinner and hydrophilic, and present a surface with wider peaks. We found that plasma treatment promotes substantial changes on the PEMs and that 20s of exposure time is enough to perform these changes. In all cases, after plasma treatment, PEMs’ thickness and free charge distribution were reduced and wettability was enhanced.

Hydrophilization of liquid surfaces by plasma treatment

The impact of the cold radiofrequency air plasma on the surface properties of silicone oils (polydimethylsiloxane) was studied. Silicone oils of various molecular masses were markedly hydrophilized by the cold air plasma treatment. A pronounced decrease of the apparent water contact angles was observed after plasma treatment. A general theoretical approach to the calculation of apparent contact angles is proposed. The treated liquid surfaces demonstrated hydrophobic recovery. The characteristic time of the hydrophobic recovery grew with the molecular mass of the silicone oil.

Cold Radiofrequency Plasma Treatment Modifies Wettability and Germination Speed of Plant Seeds

We report the possibility to modify the wetting properties of the surfaces of a diversity of seeds including: lentils (Lens culinaris), beans (Phaseolus vulgaris) and wheat (Triticum, species C9) by cold radiofrequency air plasma treatment. Air plasma treatment leads to the dramatic decrease in the apparent contact angle. Moreover, the speed of germination and yield (germination rate) of seeds can be modified by preliminary plasma treatment. The change in the wetting properties of seeds is at least partially due to oxidation of their surface under plasma treatment. Significant growth of the peaks corresponding to the nitrogen containing groups in the mass spectra of air plasma treated seeds was registered by TOF-SIMS spectroscopy.

Surface modification of poly(ethylene terephthalate) fibers induced by radio frequency air plasma treatment

The surface chemical and physical modifications of poly(ethylene terephthalate) (PET) fibers induced by radiofrequency air plasma treatments were correlated with the characteristics of the discharge parameters and the chemical composition of the plasma itself, to identify the plasma-induced surface processes prevailing under different operating conditions. Treated polymer surfaces were characterized by water droplet absorption time measurements and XPS analysis, as a function of the aging time in different media, and by AFM analysis. They exhibited a remarkable increase in hydrophilicity, accompanied by extensive etching and by the implantation of both oxygen- and nitrogen-containing polar groups. Etching was mainly a consequence of ion bombardment, yielding low molecular weight, water soluble oxidation products, while surface chemical modifications were mainly due to the action of neutral species on the plasma-activated polymer surface.

Characterization of air plasma‐treated polymer surfaces by ESCA and contact angle measurements for optimization of surface stability and cell growth

AbstractA radiofrequency air plasma has been used to incorporate new functionalities at the surface of cycloolefin polymers (Zeonex® and Topas®), polymethyl methacrylate (PMMA), styrene–acrylonitrile copolymer (SAN), and polystyrene (PS). The main goals with the plasma treatment of the different plastics were to hydrophilize the surfaces and to provide good cell culture properties. Surfaces treated at high RF power/gas flow ratios (50 to 100 W/sccm) became highly hydrophilic (water contact angles of about 5 degrees) and stable towards washing in 70% (v/v) ethanol. Those treated at lower power/gas flow ratios (3 to 10 W/sccm) were less hydrophilic and not wash‐stable. Cell growth properties of HeLa cervix carcinoma cells as good as on commercial tissue‐culture polystyrene could be obtained for Zeonex, SAN, and PS, treated at relatively low RF power/gas flow ratios. However, no untreated plastics were suitable for culturing these cells. XPS spectra features show that ester, ether/alcohol, and ester/carboxyl groups are formed during the plasma treatments of the different plastics. Measurable amounts of carboxylic acid carbon after plasma treatment were only observed for PS and Topas. Furthermore, at high RF power/gas flow ratios fluorine, aluminium and silicon were incorporated in all investigated plastics surfaces due to ablation–deposition processes in the reaction chamber. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2618–2625, 2002

A plasma etching-induced defect state in electron-irradiated n-type bulk section

Defect states induced by radio frequency air plasma etching process in n-type bulk silicon have been studied. Deep level transient spectroscopy shows that a deep center with a small electron capture cross section σtn =1.3×10−20 cm−3 and an energy level at 0.41 eV below the conduction band was induced by plasma treatment of previously electron-irradiated Si samples. The spectral dependence of optical cross sections for this defect level was measured by deep level optical spectroscopy, showing that the defect has a strong electron-phonon coupling with a Franck–Condon shift of about 0.4 eV, and that the defect core is repulsive for electrons. The defect anneals out above 400 K, and is also slightly unstable at room temperature.