Air Dielectric Barrier Discharge Research Articles

Study of the surface modification of a Nylon-6,6 film processed in an atmospheric pressure air dielectric barrier discharge

A Nylon-6,6 film has been treated using an atmospheric pressure air dielectric barrier discharge (DBD). The resultant surface modifications were studied using X-ray photoelectron spectroscopy (XPS), contact angle measurement and secondary ion mass spectrometry (SIMS). The surface oxidation arising in the DBD discharge was found to arise in two stages: in the first stage, the creation of the carbon sites singly bonded to oxygen is dominant, the second stage leads to further conversion of such lightly oxidised carbons to those more heavily oxidised. The marked increase found in the hydrophilicity of the surface post-treatment is in the main believed to be associated with the earlier outcome. Partial recovery of the surface contact angle values is found for the treated samples following extended storage in ambient air. The final contact angle obtained for the treated samples was ∼50°, still reduced significantly from that of 83.5° for the untreated material.

Surface oxygenation of polypropylene using an air dielectric barrier discharge: the effect of different electrode?platen combinations

Polypropylene film has been modified in an air dielectric barrier discharge using two different electrode–platen configurations: stainless steel wire electrode–rubber platen or ceramic electrode–aluminium platen combinations. Modified films were characterised by static contact angle measurements, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (ATR–FT-IR). Surface hydrophilic modification appears to be governed by the presence of low-molecular weight oxidised functionalities using XPS and SIMS techniques. Irrespective of the type of electrode–platen combination used to obtain the discharge, oxygenated functionalities of identical nature are formed on the polymer surface. However, the degree of oxidation obtained by the discharge using the wire electrodes with the rubber platen was considerably greater. Further increase in the observed hydrophilicity due to molecular rearrangement and development of stable oxygenated functionalities was evident after 1 month of post-processing analysis.

Photostability and dipole orientation of air dielectric barrier discharge processed PVC copolymer

Surface modification of a PVC copolymer film was performed in an air dielectric barrier discharge (DBD) to investigate the photostability and effect of the streamer discharge on the polymer surface. Characterisation of the modified surface by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) techniques showed formation of oxidised carbon functionalities at the expense of the saturated alkyl components. Simultaneous oxygenation and hydrophilisation of the air DBD processed copolymer film was revealed by the complementary variation in contact angle and O/C ratios with respect to the applied discharge dose. On the basis of XPS derived Cl/C ratio, the concentration of the C Cl component of the C (1s) envelop and depth profiling of Cl − ions from SIMS for the modified film showed a selective abundance of chlorinated alkyl chains on the polymer surface. Stability of chemical modifications induced by DBD processing in air was investigated by analysing one-month aged treated film. Since there appears to be no change in concentration of the CCl bonds (no loss of Cl) present, it is concluded that the UV radiation emitted from the discharge does not photo-degrade the PVC copolymer surface.

Surface oxygenation of polypropylene using an air dielectric barrier discharge: the effect of different electrode–platen combinations

Polypropylene film has been modified in an air dielectric barrier discharge using two different electrode–platen configurations: stainless steel wire electrode–rubber platen or ceramic electrode–aluminium platen combinations. Modified films were characterised by static contact angle measurements, X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (ATR–FT-IR). Surface hydrophilic modification appears to be governed by the presence of low-molecular weight oxidised functionalities using XPS and SIMS techniques. Irrespective of the type of electrode–platen combination used to obtain the discharge, oxygenated functionalities of identical nature are formed on the polymer surface. However, the degree of oxidation obtained by the discharge using the wire electrodes with the rubber platen was considerably greater. Further increase in the observed hydrophilicity due to molecular rearrangement and development of stable oxygenated functionalities was evident after 1 month of post-processing analysis.

The effect of an air-dielectric barrier discharge on the surface properties and peel strength of medical packaging materials

In this paper we report and discuss the effect of air dielectric barrier discharge (DBD) surface treatments on adhesion, using poly(ethylene)/poly(ethylene terephthalate) (PE/PET) film and non-woven PE (Tyvek ®) medical packaging materials. The modification of the surface properties of the treated samples has been studied using X-ray photoelectron spectroscopy (XPS), contact angle and peel strength measurements. The influence of the surface treatment parameters, such as the energy deposited by the discharge, the inter-electrode gap and the treatment time, when related to the surface characteristics, allowed establishment of the relationship between such parameters and the properties of the DBD treated samples. Of the three process variables investigated the duration of the treatment has a statistically significant effect on the surface modification. It was found that very short air-DBD treatment (fractions of a second) markedly and uniformly modify the surface characteristics for both Tyvek ® and PE/PET. The treated materials show remarkable stability with ageing time. Improved adhesion properties, with an increase in the peel strength and a greater adhesive transfer are also observed after DBD treatment. Finally, the surface properties investigated tend to reach a plateau following approximately 1 s of processing.

Spatio-temporal dynamics of discharge domains in a dielectric barrier discharge device

The spatio-temporal correlation of discharge filaments in dielectric barrier discharges in air at atmospheric pressure is studied using an optical method. The stable filament patterns are achieved by using water electrodes, which serve both as coolants and transparent media for observation. It is found that the time interval between the two discharges of a filament in two consecutive half-cycles alternates between the long one and the short one, in general. An equation describing breakdown/termination of discharges is suggested by considering the effect of accumulated charges on the dielectric surface, and the experimental phenomena mentioned above can be explained using this equation. It is found in our experiments that the mapping of the delay time sequence for a filament has metastability with certain fluctuation features. The stable filament pattern can be divided into discharge domains. Each domain consists of several neighbouring filaments. The discharges of the filaments inside a domain are cooperatively correlated, while those of neighbouring domains are most likely competitively correlated.

Approach of the Physical and Chemical Specific Properties of Pulsed Surface Dielectric Barrier Discharges in Air at Atmospheric Pressure

AbstractInvestigations were carried out on point-to-plane dielectric barrier discharges with two different gas gap lengths (d = 0 and 2 mm), energized with two different high voltage power supplies providing one an ac signal at 15 kHz and the other a pulsed signal with a same repetition rate. Correlations between the electrical properties and the behavior of the plasma in these different situations were established through ozone generation, and by the way O radicals net production, checking for this purpose that in our operating conditions gas­heating influence remained minor. Using the representation ozone concentration vs. charge amount transferred through current pulses, the specific electrical and thus physical properties of pulsed surface discharges are put in light; in these discharges, compared to ac and pulsed volume discharges, current pulses exhibit, for a given charge per pulse, the highest amplitudes and the shortest durations.

Temporal Behaviour of Micro-discharge in Dielectric BarrierDischarges

A special dielectric barrier discharge (DBD) device consisting of twowater electrodes has been designed. The temporal behaviour of the micro-discharge(filament) in the DBD in air at atmospheric pressure is measured byusing an optical method. The nonsymmetrical characteristic of the filamenthas been discovered for the first time. We propose an equation regarding the dischargemoment by considering the memory effect of the accumulatedcharge and the influence of the fluctuation. The results deduced fromthe equation give a good explanation of the experimental phenomenon,which show that the decay time constant of the accumulated charges ismuch larger than 100 µs. The relative intensity offluctuation amplitude is in the range 2-4% under the presentexperimental conditions.

Modification of the surface properties of a polypropylene (PP) film using an air dielectric barrier discharge plasma

Modification of the surface properties of a polypropylene (PP) film using an air dielectric barrier discharge has been studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The atmospheric pressure air discharge is found to modify the PP surface in both morphology and composition, as expressed in the following outcomes: the spherulitic features of the surface of the pristine PP film change into randomly-shaped surface protrusions, with the surface roughness increasing as the processing time is extended; heavily oxidized carbon species are found on the plasma-processed surface and the contact angle is also reduced dramatically from 93.7° for the untreated surface to 53.8° post-treatment. After long-term storage in ambient air, the much lowered surface contact angle of the processed PP film is found to in part recover. Effective plasma-induced chemical etching appears to equilibrate after 25% of the surface carbon is oxidized. The CH3 functionalities in the PP are believed to be oxidized preferentially by the air discharge plasma.

Self-Organized Filaments in Dielectric Barrier Dischargein Air at Atmospheric Pressure

The self-organized filament pattern created by dielectric barrier dischargesin air at atmospheric pressure is investigated experimentally. The densityand dimension of filament are analysed quantitatively. The experimentalresults show that the distance between neighbouring filaments decreases with theincreased applied voltage or with the decreased width of the gas gap. Also,the diameter of the filament decreases with the increased applied voltagesor with the decreased width of the gas gap.

Surface modification of polyimide using dielectric barrier discharge treatment

We report on a novel method for the surface modification of polymers by direct exposure to a dielectric barrier discharge (DBD) at atmospheric pressure and room temperature. The polymer under treatment is located directly on the grounded electrode and serves at the same time as the discharge barrier. So far DBD treatment of the unfilled and Al 2O 3-filled commercially available polyimide foils have been investigated as a function of specific discharge energy. The morphological effects of the DBD treatment have been analysed by optical microscopy, SEM, AFM, and chromatic coding distance measurement while XPS was used for analysis of the chemical surface composition. The results can be summarised as follows: Firstly, the etching rate of the polyimide (PI) surface by DBD in air is rather high leading to a pronounced roughening within some tens of seconds. Secondly, the attack is dependent on whether the polyimide contains a filler, which is added to improve the thermal conductivity of the material. In this case the etching lays bare the grains of the filler but is spatially rather uniform. The surface roughening increases the bond strength to coating layers. Finally, in the unfilled material crater-like structures are observed which are attributed to the repetitive ignition of discharge filaments in the same location.

The development of dielectric barrier discharges in gas gaps andon surfaces

Dielectric barrier discharges (DBDs) occur in configurations whichare characterized by a dielectric layer between conducting electrodes. Twobasic configurations can be distinguished: a volume discharge (VD)arrangement with a gas gap; and a surface discharge (SD) arrangement withsurface electrode(s) on a dielectric layer and an extensive counter electrodeon its reverse side. At atmospheric pressure the DBD consists of numerousmicrodischarges (VD) and discharge steps (SD), respectively, their numberbeing proportional to the amplitude of the voltage. These events have a shortduration in the range of some 10 ns transferring a certain amount of chargewithin the discharge region. The total transferred charge determines thecurrent and hence the volt-ampere characteristic of each arrangement. Themicrodischarges (discharge steps) have a complicated spatial structure. Thedischarge patterns on the dielectric surface depend on the polarity and amplitudeof the applied voltage as well as on the specific capacity of the dielectric.Experimental findings on DBDs in air and oxygen are presented and discussed.On the basis of a self-consistent two-dimensional modelling the temporal andspatial development of a microdischarge and discharge step are investigatednumerically. The results lead to an understanding of the dynamics of DBDs.Although in VD arrangements cathode-directed streamers appear especially inelectronegative gases, their appearance is rather unlikely in SD arrangements.The application of DBDs for plasma-chemical reactions is determined by theproductivity, with which the energy of the electric field can be converted intointernal states of atoms and/or molecules. Depending on the desired product itcould be both the generation of internal electronic states of molecules oratoms and dissociation products of molecules. The discharge current andcurrent density of DBDs in both the SD and VD arrangements as well as the energyrelease and energy density distribution in the discharge region are presented.As an example the effectiveness of the energy conversion into ozone productionis detailed. Some peculiarities of the discharge parameters, for instance thecorrelation between discharge patterns (microdischarges or discharge steps)and surface charge density, are discussed.

Comparison of dielectric barrier discharge in air, nitrogen and argon at atmospheric pressure

This paper reports the results of electrical characterization of dielectric barrier discharge (DBD) generated in air, nitrogen and argon at atmospheric pressure. Polycarbonate plate of thickness 1 mm was used as a dielectric barrier in a specially designed hemispherical-plane electrode system. A nonuniform filamentary type of discharge was observed in air. Introducing nitrogen and argon gas at controlled flow rate of 1-2 liters / minute resulted a more homogeneous discharge at a frequency of 28 kHz of the AC source. The discharge was investigated for two values of electrode gap of 1 mm and 2 mm by varying the applied voltage. The number of current pulse per half cycle and the magnitude of the discharge current were found to be higher in the case of air discharge in comparison to the discharge in nitrogen and argon. The characteristics of the discharge in air in the absence dielectric barrier was also examined and interestingly it was found that in this case the filamentary discharge turned to a glow discharge for specific value of applied voltage and electrode spacing. Keywords: DBD; Glow Discharge; hemispherical-plane electrode; filamentary discharge; Polycarbonate Sheet DOI: 10.3126/kuset.v6i2.4006Kathmandu University Journal of Science, Engineering and Technology Vol.6. No II, November, 2010, pp.6-12

An Investigation of the Effect of Electrode Geometry and Frequency of Power Supply in the Homogeneity of Dielectric Barrier Discharge in Air

An experimental investigation of dielectric barrier discharge (DBD) produced in air isreported in the present paper. The discharge was produced by applying 0?20 kV AC source atfrequency 10?30 kHz. The main objective of the study was to investigate the dependence ofthe discharge homogeneity on the frequency of applied source and the geometry of theelectrodes. For this propose, three different types of electrodes were used. The discharge wassystematically investigated on an extended range of electrical parameters using highfrequency digital oscilloscope. Non-thermal nature of the discharge was tested by thetreatment of hydrophobic polymer surface by measuring the change in contact angle withwater drops.Key words: DBD; electrode geometry; contact angle measurement; surface treatmentDOI: 10.3126/kuset.v6i1.3316 Kathmandu University Journal of Science, Engineering and Technology Vol.6(1) 2010, pp96-101