Slobodan Milošević

Modification of ink-jet paper by oxygen-plasma treatment

A study on oxygen-plasma treatment of ink-jet paper is presented. Paper was exposed to a weakly ionized, highly dissociated oxygen plasma with an electron temperature of 5?eV, a positive-ion density of 8 ? 1015?m?3 and a density of neutral oxygen atoms of 5 ? 1021?m?3. Optical emission spectroscopy (OES) was applied as a method for detection of the reaction products during the plasma treatment of the paper. OES spectra between 250 and 1000?nm were measured continuously during the plasma treatment. The wettability of the samples before and after the plasma treatment was determined by measuring the contact angle of a water drop. The appearance of the surface-functional groups was determined by using high-resolution x-ray photoelectron spectroscopy (XPS), while changes in the surface morphology were monitored with scanning electron microscopy (SEM). Already after 1?s of the plasma treatment the surface, which was originally hydrophobic, changed to hydrophilic, as indicated by a high absorption rate of a water drop into the paper. The OES showed a rapid increase of the CO and OH bands for the first few seconds of the plasma treatment, followed by a slow decrease during the next 40?s. The intensity of the O atom line showed reversed behaviour. The XPS analyses showed a gradual increase of oxygen-rich functional groups on the surface, while SEM analyses did not show significant modification of the morphology during the first 10?s of the plasma treatment. The results were explained by degradation of the alkyl ketene dimer sizing agent during the first few seconds of the oxygen-plasma treatment.

Optical emission spectroscopy characterization of oxygen plasma during treatment of a PET foil

Optical emission spectroscopy (OES) analysis of inductively coupled RF oxygen plasma during plasma treatment of a 23 µm thick polyethylene terephthalate (PET) foil is presented. Plasma was generated in pure oxygen at a pressure of 75 Pa with a RF generator at a frequency of 27.12 MHz and an output power of 300 W. The electron temperature was about 6 eV, the density of charged particles about 1016 m−3 and the density of neutral O atoms about 1022 m−3. Spectra were measured in the range from 250 to 950 nm by means of an optical spectrometer. For the first 10 s of plasma treatment the OES showed the presence of oxygen radicals only. Later, the OES spectra became richer with significant emission from CO and OH, which was attributed to PET oxidation. Simultaneously, the O peaks decreased significantly. After prolonged plasma treatment, the O peaks recovered, the CO band vanished while the OH and H peaks still persisted. In the final period of the treatment only atomic oxygen lines remained. The results showed that OES analysis was a powerful method for studying the evolution of PET oxidation by plasma treatment.

Monitoring Oxygen Plasma Treatment of Polypropylene With Optical Emission Spectroscopy

Optical emission spectroscopy was used to monitor the evolution of chemical reactions taking place on the surface of semicrystalline polypropylene during oxygen plasma treatment. The optical spectra were continuously acquired during treatment at different pressures (20-140 Pa). The time evolution of different excited radicals (O, H, CO, OH, and CH) allowed for the estimation of the chemical reactions. The oxidation of the material started as soon as the plasma was ignited and slowly intensified until the evaporation of the material was indicated by the appearance of the CH band. As the CH band appeared, a rapid increase in CO and OH was observed, together with a drop in O and a maximum in H. A well-defined minimum in the time needed for the appearance of the CH band was found versus the pressure. The results were explained by heating the polymer due to exothermic physical and chemical reactions and cooling by the surrounding gas.

Application of extremely non-equilibrium plasmas in the processing of nano and biomedical materials

Some applications of extremely non-equilibrium oxygen plasma for tailoring the surface properties of organic as well as inorganic materials are presented. Plasma of low or moderate ionization fraction and very high dissociation fraction is created by high frequency electrodeless discharges created in chambers made from a material of low recombination coefficient. The O atom density often exceeds 1021 m−3 which allows for rapid functionalization of carbon-containing materials. Surface saturation with polar oxygen-rich groups is achieved in a fraction of a second and further exposure leads to etching. The etching is often non-uniform and results in nano-structuring of surface morphology. A combination of rich morphology and saturation with polar functional groups allows for a super-hydrophilic character of originally hydrophobic materials. Polymer composites are etched selectively so the polymer component is removed from the sample surface, leading to modified surface properties. Furthermore, such a treatment allows for distinguishing the distribution and orientation of fillers inside the polymer matrix. The exposure of inorganic materials to non-equilibrium oxygen plasma causes one-dimensional growth of metal oxide nanoparticles, thus representing a unique technique for the rapid catalyser-free growth of nanowires.

Inductively Coupled RF Oxygen Plasma Studied by Spatially Resolved Optical Emission Spectroscopy

Inductively coupled RF oxygen plasma generated by inductive coil wrapped around a linear glass tube is studied. Images of plasma properties in the linear reactor are presented. Plasma diagnostics was performed by spatially resolved optical emission spectroscopy.

Multiple vs. single harmonics AC-driven atmospheric plasma jet

In this paper, we report a comparison between the most commonly used single harmonics (sine voltage waveform) and the original multiple harmonics AC-driven atmospheric-pressure plasma jet. The designed multiple harmonics source was applied to a single-electrode plasma jet. In this research, we characterized and studied the advantages of a single-electrode jet which was powered with multiple harmonics voltage waves, fundamental frequency was varied between 5 and 60 kHz. Optical emission spectroscopy, electric probes and plasma jet visible length measurements lead to the conclusion that the optical emission intensity of emitting plasma species correlates with the discharge current RMS (Root Mean Square), whereas the jet visible length correlates with the electrode discharge voltage amplitude. These properties of the plasma jet cannot be obtained with single harmonics AC-driven plasma jets.

Interaction of Oxygen Plasma With Aluminium Substrates

Inductively coupled oxygen plasma is widely used for material processing. Optical emission spectroscopy using fast miniature fiber spectrometer was used for plasma characterization and process monitoring. The images of plasma and accompanying spectra during interaction with aluminium foil are presented.

Optical Emission From Oxygen Plasma in E and H Modes

Highly reactive oxygen plasma with a very high dissociation fraction of oxygen molecules is often created in electrodeless discharges. The discharge runs either in the E or H mode. The E mode is obtained at low power while the H mode dominates at high power. The transition between two modes is easily observed by the naked eye or, even better, by optical emission spectroscopy. In this paper, we show major differences between the two modes obtained in an experimental plasma reactor with a 1200-W RF generator operating at the frequency of 13.56 MHz.