AP08_4.vp 1 Introduction Non-equilibrium atmospheric pressure discharges have recently been used in emerging novel applications such as the surface modification of polymers, the absorption or re- flection of electromagnetic waves, biomedical treatments and plasma-aided combustion [1]. Among these various interest- ing new applications, the interaction of atmospheric pressure “cold” plasmas with a biological medium promises to open new horizons in the medical and environmental fields. The main methods of sterilization, i.e., inactivation of living microorganisms, are based on thermal treatment (dry or moist heat), chemical treatment (e.g., EtO, H2O2) or expo- sure to ionizing radiation (X-ray, gamma radiation, e-beams). These methods have specific drawbacks linked to their condi- tions of operation, e.g., the toxicity of the active agent used, the temperature conditions, or the size of the installation. Clearly, plasma sources have some advantages such as low temperature (at or near room temperature), no risk of arc- ing, operation at atmospheric pressure, portability, optional hand-held operation, etc. Therefore low-temperature non- -equilibrium plasmas are playing an increasing role in biomedical applications, and reliable, user-friendly sources need to be developed. A point-to-plane corona discharge at atmospheric pressure is one of the atmospheric pressure discharges applicable for studying the interactions of atmo- spheric ions with microorganisms such as bacteria and fungi [2–4]. The bactericidal or fungicidal effect of corona dis- charge can be studied directly on a gel medium (agar), which is a gelatinous substance chiefly used as a culture medium for microbiological work. This technology minimizes the risk of accidental contamination of the samples, and makes the experiments relatively simple. Corona discharges are usually realized in such a way that one of the electrodes has a small radius of curvature. This makes the electric field intensity very high close to this elec- trode in comparison to other points in the gap. Electrons and positive ions are egnerated. If the gas contains an electro- negative component, electrons can attach to it to produce negative ions. Afterwards the ions drift to the corresponding electrode according to particle polarity. Their movement is broken by collisions with neutral atoms and molecules. This process can be classified as friction. Ions drifting to an elec- trode with a low radius of curvature (further referred to as a plate electrode) can also make the neutral gas move. This im- portant phenomenon is called electric wind [5]. Due to ionic wind the gel surface is deformed, which results in a change in the corona discharge geometry. The discharge current and voltage change during the experiments in dependence on the surface deformation and the gel medium. 2 Experimental part Fig. 1 shows the scheme of the apparatus used for gene- rating a point-to-plane negative corona discharge at atmo- spheric pressure. Each type of gel electrode was placed in a standard Petri dish (90 mm in diameter). The size of the gel layer electrode varied in the analyzed samples, the mean value being 8 mm. The following gel types were used: blood agar, nutrient agar, Endo agar. All were prepared from defined fabric substrates. Six samples of each type of agar were used; the dates of sam- ple preparation and storage of the samples in a cooling box varied. The point corona electrode was realized by an intra- muscular medicinal hollow needle with an outer diameter of 0.7 mm. The needle had a sharpened angle of 15 degrees. The position of the hollow needle was adjusted by a micro- © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 27 Acta Polytechnica Vol. 48 No. 4/2008 Influence of a Point-to-Plane DC Negative Corona Discharge on Gel Surfaces Y. Klenko, V. Scholtz Point-to-plane corona discharge is widely used for modifying polymer surfaces for biomedical applications and for sterilization and decontamination. This paper focuses on an experimental investigation of the influence of the single-point and multi-point corona discharge electric field on gel surface. .Three types of gelatinous agar were used as the gel medium: blood agar, nutrient agar and Endo agar. The gel surface modification was studied for various time periods and discharge currents. Keywords: Point-to-plane corona, electrohydrodynamic deformation, gel ion-conducting electrode. Fig. 1: Schematic of an open-air corona exposure single-point set-up with a Petri dish 90 mm in diameter metric screw placed inside the needle holder. The position of the Petri dishes could also be changed in two directions per- pendicular to the needle movement and also perpendicular to each other. The position change of the hollow needle and the Petri dish was measured with precision 0.01 mm. When the needle was used as an electrode in the discharge regime, it was connected to a high voltage supply. The same needle was used detecting deformation in the measurement regime. The conductive connection between the tip of the hollow needle and the gel surface was checked using an ohm- meter. Initially, the tip of the hollow needle was placed 6 mm above the gel surface and the positions of the needle and the high voltage source set-up remained unchanged dur- ing corona treatment. In the deformation measurements the dimple depth was measured as the change in the distance between the electrodes. The needle was moved perpendicu- larly toward the gel surface. the contact between the needle tip and the gel surface was detected by the ohmmeter. The exposition times varied (1, 2, 4, 8, 16 min). 3 Results Fig. 3 is a photograph of the gel surface deformations caused by the corona discharge. A matrix multi-point-to- -plane corona discharge was used in this case. Fig. 3 shows the gel deformation due to the multi system point-to-plane corona discharges. Due to their simplicity, the measurements were made with a single-needle-to-gel elec- trode system. Fig. 4. shows the dependence of dimple depth on the gel surface exposition in a point-to-plane corona discharge. During the measurements, the corona current decreased from initial value (50 �A) according to the gel electrode deformation. The dependence of dimple depth on point-to-plane co- rona initial current is show in Fig. 5. The duration of the gel surface exposition in the corona discharge was 16 minutes. The diameter of the dimple at 0.3 mm depth was taken as a standard characteristic dimension of the area affected by the point-to-plane corona discharge. After the influence of the corona, the needle was moved 6.3 mm towards the gel sur- face, and standard diameter d was measured. Fig. 6 presents 28 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 48 No. 4/2008 Fig. 2: Photograph illustrating the experimental set-up Fig. 3: Photograph of a Petri dish showing the gel surface defor- mation caused by the corona discharge exposition 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 0 5 10 15 20 t [min] D im p le d e p th [m m ] Fig. 4: Dependence of dimple depth on exposition time at dis- charge current 50 �A 0 0,5 1 1,5 2 2,5 3 0 100 200 300 400 I [mA] D im p le d e p th [m m ] 16 min Fig. 5: Dependence of dimple depth on discharge current (expo- sition time 16 min) the process of measuring the standard diameter. The depend- ence of the standard diameter on exposition duration is shown in Fig. 7. The initial corona current was 50 �A. The dependence of standard diameter d on the initial co- rona current is shown in Fig. 8. The exposition duration was 16 minutes. 4 Conclusion We developed an apparatus that generates a DC negative point-to-plane corona discharge of various parameters in air at atmospheric pressure. In addition, we attempted to de- velop a method enabling a quantitative evaluation of the action the discharge on an artificial bacterial culture. We also studied the influence of the electric field of the corona dis- charge on the substrate formed by the agar gel. The electrohydrodynamic deformation of the substrate was observed. The gel surface was deformed by the ionic wind in the point-to-plane corona. The deformation of the gel sur- face was comparable to the distances between the electrodes used in sterilization experiments [2, 3]. The electrohydro- dynamic deformation effect redistributed the corona current during gel exposition to a corona. Moreover Figs. 4–7 show that the gel surface deformation cannot be predicted for a specific gel type (although a relatively precise method of gel surface position determination was used). The variation of the deformation characteristic dimensions may be explained by the fact that the water content in the used agar plates used here changed during storage, and consequently the gel elec- trode viscosity also changed. Acknowledgments The research presented in this paper was supervised by Doc. J. Píchal, MUDr. Ing. V. Kříha and Prof. L. Aubrecht, FEE CTU in Prague, and has been supported by GAČR grant No. 202-03-H162 “Advanced Study in Physics and Chemistry of the Plasma”. References [1] Laroussi, M., Tendero, C., Lu, X., Alla, S., Hynes, W. L.: Inactivation of Bacteria by the Plasma Pencil. Plasma Pro- cess Polym. 2006, 3, p. 470–473. [2] Scholtz, V., et al.: Corona Discharge: a Simple Method of its Generation and Study of its Bacterial Properties. Cz. J. Phys., Vol. 56 (2006), Suppl. B, p. 1333–1338. [3] Scholtz, V., et al.: The Study of Bactericidal Effects of Corona Discharge at Atmospheric Pressure. In Proceed- ings of the 33rd EPS Conference on Plasma Phys. Rome (Italy), 2006, Vol. 301, p. 4.007. [4] Sigmond, R. S., Kurdelova, B., Kurdel, M.: Action of Co- rona Discharges on Bacteria and Spores. Cz. J. Phys., Vol. 49 (1999), No. 3, p. 405–420. [5] Kurdel, M., Morvova, M.: DC Corona Discharge Influ- ence on Chemical Composition in Mixtures of Natural Gas with Air and is Combustion Exhaust with Air. Cz. J. Phys., Vol. 47 (1997), No. 2, p. 205–215. Yuliya Klenko e-mail: klenkj1@feld.cvut.cz Vladimir Scholtz e-mail: vscholtz@gmail.com Czech Technical University Faculty of Electrical Engineering Technická 2 166 27 Praha, Czech Republic © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 29 Acta Polytechnica Vol. 48 No. 4/2008 Fig. 6: The process of measuring standard diameter d 0 2 4 6 8 10 12 14 16 0 5 10 15 20 t [min] d [m m ] Fig. 7: Standard diameter increment with an increase in dis- charge current (influence time 16 min) 0 5 10 15 20 25 30 35 0 100 200 300 400 I [mA] d [m m ] 16 min Fig. 8: Standard diameter dependence of treatment time (dis- charge current 50 �A) << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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