Mirko Černák

Atmospheric-pressure diffuse coplanar surface discharge for surface treatments

We report results from a plasma source; a diffuse coplanar surface discharge (DCSD), which is capable of generating macroscopically uniform thin layers of diffuse plasmas in air and other reactive gases at atmospheric pressure. DCSD is a type of dielectric barrier discharge generated on the surface of a dielectric barrier with embedded electrodes, which appears to be advantageous to surface treatment and deposition processes. Preliminary results on hydrophilization of polypropylene nonwoven fabric are also presented.

Atmospheric-pressure plasma treatment of polyester nonwoven fabrics for electroless plating

Abstract Atmospheric-pressure non-thermal plasmas have been increasingly promoted for polymer surface modifications. In this paper, atmospheric-pressure nitrogen plasma was used to render a polyester nonwoven fabric hydrophilic and facilitate absorption of a palladium catalyst in order to provide a catalytic surface for the deposition of electroless nickel. The plasma was produced in a surface barrier discharge generating a thin plasma layer in good contact with the fabric fibers. The optimum quality nickel coating was obtained for a 1 s treatment time. Treatment times in excess of 1 s resulted in a reduction of the nickel plating deposition rate, uniformity and adhesion values. The plasma-induced surface changes were characterized by liquid strike-through time measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. Because of atmospheric-pressure operation, very short treatment times, and its robustness the method has the potential to be used in line with standard metal plating lines.

Hydrophilization of polypropylene nonwoven fabric using surface barrier discharge

Abstract Surface dielectric barrier discharges (SDBD), which find widespread industrial applications in ozone production, were used to hydrophilize light-weight polypropylene nonwoven fabric (PPNF) samples. The samples were treated in nitrogen plasma generated by SDBD at atmospheric pressure. The hydrophilicity of the samples was examined as a function of the storage time using a standard strike-through test. The surface chemical composition was characterized by X-ray photoelectron spectroscopy. Because of very short treatment times obtained (∼1 s) and its simplicity the method has the potential to be used in-line with standard high-speed PPNF production lines, laminating, printing and metal plating lines, etc.

STREAMER MECHANISM FOR NEGATIVE CORONA CURRENT PULSES

Current wave forms of initial stages of breakdown and corona formation in a short negative point-to-plane gap have been measured with a nanosecond time resolution in air, O2, and N2 at pressures 13.33–100 kPa, and at various overvoltages. The experiments revealed the existence of a stepped form of negative corona Trichel pulses in O2 at atmospheric pressure. To test existing models for the negative corona pulse formation, effects of changing cathode secondary electron emission were studied using a brass cathode coated by CuI and graphite. It is concluded that a negative corona (Trichel) pulse is associated with the ignition of a cathode-directed streamer in the immediate vicinity of the cathode and the subsequent formation of a glow-discharge-type cathode region at the streamer arrival to the cathode. The implications of these results to negative corona applications are discussed.

Numerical simulation of streamer–cathode interaction

A self‐consistent fluid model has been used to analyze streamer arrival at the cathode and its transformation to the stationary cathode fall in a positive point–to–plane corona discharge in N2 at 26.7 kPa. The model is based on a description of the electron and the ion kinetics by one‐dimensional continuity equations coupled with Poisson’s equation. The ions and electrons are assumed to be limited to a cylindrical channel with fixed radius and the field is computed using the method of disks. The computed current induced by the streamer–cathode interaction with a small cathode probe is compared with that measured experimentally. The cathode probe signal consists of an initial sharp current spike due to the displacement current followed, some 20 ns later, by a lower current hump due to the ion arrival at the cathode. The current signal is relatively insensitive to changes in the secondary electron emission coefficients. The results obtained indicate that the intense ionization and associated light flash exp...

Magnetic Nanoparticles: From Design and Synthesis to Real World Applications

The increasing number of scientific publications focusing on magnetic materials indicates growing interest in the broader scientific community. Substantial progress was made in the synthesis of magnetic materials of desired size, morphology, chemical composition, and surface chemistry. Physical and chemical stability of magnetic materials is acquired by the coating. Moreover, surface layers of polymers, silica, biomolecules, etc. can be designed to obtain affinity to target molecules. The combination of the ability to respond to the external magnetic field and the rich possibilities of coatings makes magnetic materials universal tool for magnetic separations of small molecules, biomolecules and cells. In the biomedical field, magnetic particles and magnetic composites are utilized as the drug carriers, as contrast agents for magnetic resonance imaging (MRI), and in magnetic hyperthermia. However, the multifunctional magnetic particles enabling the diagnosis and therapy at the same time are emerging. The presented review article summarizes the findings regarding the design and synthesis of magnetic materials focused on biomedical applications. We highlight the utilization of magnetic materials in separation/preconcentration of various molecules and cells, and their use in diagnosis and therapy.

Plasma Treatment of Glass Surfaces Using Diffuse Coplanar Surface Barrier Discharge in Ambient Air

We report a study on the treatment of flat glass surfaces by ambient air atmospheric pressure plasma, generated by a dielectric barrier discharge of coplanar arrangement of the electrode system—the diffuse coplanar surface barrier discharge (DCSBD). The plasma treatment of glass was performed in both static and dynamic modes. With respect to wettability of the glass surface, treatment in static mode resulted in non-uniform surface properties, whereas dynamic mode provided a fully uniform treatment. A water contact angle measurement was used to determine the efficiency of plasma treatments in dynamic mode and also to investigate a hydrophobic recovery of plasma treated glass surfaces. The X-ray photoelectron spectroscopy measurements showed a decrease of overall carbon concentrations after plasma treatment. A deconvolution of C1s peak, showed that a short plasma treatment led to decrease of C–C bonds concentration and increases of C–O and O–C=O bond concentrations. An enhancing influence of the glass surface itself on DCSBD diffuse plasma was observed and explained by different discharge onsets and changes in the electric field distribution.

Surface analysis of groundwood paper treated by diffuse coplanar surface barrier discharge (DCSBD) type atmospheric plasma in air and in nitrogen

Abstract Paper made of groundwood was surface treated by atmospheric plasma of the diffuse coplanar surface barrier discharge (DCSBD) type in air and in nitrogen. Changes in surface composition and chemical bonding of the constituent elements were studied by X-ray photoelectron spectroscopy (XPS), and alterations in wetting were examined by contact angle measurements. Air plasma treatment resulted in strong oxidation but no N incorporation, while the ratio of the area of the O1 component (binding energy 532.1 eV) to that of the O2 component (533.2 eV) decreased, reflecting an increase in the proportion of O in C–O type bonds. Nitrogen plasma treatment followed by exposure to the atmosphere resulted in a slight N incorporation (1.5 at.%) and oxidation even more intense than observed for air plasma treatment. The O1/O2 ratio slightly increased, implying more O in C=O type bonds. The time dependence of surface oxidation showed a local maximum at treatment time of approximately 2 s for both the air and nitrogen plasmas.

Experimental confirmation of positive-streamer-like mechanism for negative corona current pulse rise

Current growth waveforms corresponding to initial phases of negative corona current pulses were measured in nitrogenous gas mixtures at pressures of 6.67-40 kPa. The measurements showed that the steep pulse rise is not dependent on cathode secondary emission processes for pressures above 30 kPa. This, together with a discontinuous transition in the current waveforms observed with increasing gap voltage in N2 at pressures of 20-26.6 kPa, implies that the feedback-to-cathode Townsend ionization mechanism was supplanted by a faster streamer-like mechanism. At pressures below 20 kPa a positive-streamer-like wave results in complex Trichel pulse shapes with a step on the pulse leading edge and a hump on the pulse trailing part.

Atmospheric-pressure plasma treatment of ultrahigh molecular weight polyethylene fibers

The performance properties of composite materials reinforced by ultrahigh molecular weight polyethylene (UHMW-PE) fibres depend critically on the fiber/matrix interfacial characteristics. The chemical inertness and very low surface energy of UHMWPE fibers, however, results in a fiber/matrix interfacial strength much less than ideal for such applications [1]. Several teams made remarkable achievements in the surface modification of UHMW-PE by low-pressure plasma treatment at pressures below one Torr (130 Pa) [2–6]. However, these low-pressure plasma treatments require vacuum systems and do not lend themselves easily to an industrial implementation. In this study UHMW-PE fibers were treated by a nitrogen plasma at atmospheric pressure, where the plasma treatment can potentially be realised with less technical effort. A nitrogen plasma was chosen because of its low degrading effect and high radical density creation [6, 7]. A commercially available UHMW-PE filament bundle of 150 filaments (Dyneema SKX 65, dtex 165) was cleaned with acetone before the treatment. The plasma treatment was performed using a pulsed surface discharge reactor that consisted of two on-axis-arranged electrodes housed in a glass chamber [8]. Nitrogen of a technical purity was introduced into the chamber with a flow rate of 1 cm3 s−1. The ground stainless-steel tubular anode was 1 mm in inner diameter. The cathode was a 15 mm-diam. hemispherically capped brass rod with a 2 mm-diam. hole in its axis. The distance between electrodes was adjusted to 15 mm. The treated filament bundle moved on the axis of the electrode system with a speed of 100 mm s−1. The cathode was connected with a tyratron source of pulsed high voltage with a pulse frequency of 100 Hz, a peak voltage of 25 kV, pulse rise time of 75 ns, and pulse half-width of 400 ns. The discharge power was approximately 10 W. To illustrate the effect of the plasma treatment on fiber surface properties, the fiber/rubber matrix adhesion values measured using the untreated and treated fibers were compared. The samples were prepared by pressing the filament bundle between two slides from a conventional polybutadiene rubber blend. Subsequently, the samples were vulcanised at a temperature of 145 ◦C. Adhesion of the fibers to rubber was characterised in a standard H-peel test by the force required to draw out the filament bundle of a rubber block. The adhesion values (the averages of twenty measurements) for the reference and plasma-treated fibers were 1.7 and 2.5 kN m−1, respectively, i.e. an increase of 44% was obtained by the plasma treatment. As stated by Jacobasch et al. [9], some insight into the adhesion behavior of polymer surfaces can be obtained also by zeta potential measurements with varied electrolyte concentration. Preliminary results of our ζ -potential measurements are shown in Fig. 1. From the results it is evident that anions (Cl− and OH−) present in KCl electrolyte are preferably adsorbed by the treated fiber surface. The observed decrease in negative ζ -potential values due to the plasma treatment (corresponding to a decrease of the electrical double layer thickness [9]) indicates a higher hydrophilicity of the plasma-treated fibers. An increase in the pH corresponding to the zero ζ -potential (isoelectric point) indicates a creation of basic surface groups by the plasma-treatment. This is consistent with the basicity of polyethylene tapes treated by atmospheric pressure nitrogen plasma [10] found on the base of contact angle measurements. Our ζ -potential measurements, in an agreement with the results of Gresseer et al. [11] and Wakida et al. [12], affirm that ζ -potential measurements can be a useful technique in determining of technologically