3 Results and Discussion In the surfatron plasma we can distinguish two different regions: the plasma inside the discharge tube and the effluent plasma flame with afterglow. As the last part of this paper is dedicated to the improvement of hydrophilic properties of the studied samples using interaction of the surfatron plasma jet with the sample, the part of the paper dealing with OES is focused on the region where the treatment occurs – the effluent plasma. Additionally, only the very end of the discharge tube (where the mixing of plasma with atmospheric air also occurs due to back diffusion of air into the tube) is investigated.
3.1 Overview spectra
The overview optical emission spectrum is often used to estimate the composition of the plasma. However, one must keep in mind that the OES cannot provide complete information, as it does not reveal the species that are in the ground or non-radiating state or the species whose emission is outside the measured wavelength range. The direct comparison of emission intensity of different plasma species cannot provide dependable information about the ratio of these species’ densities. The overview spectra of the plasma inside and outside the tube can be seen in Fig. 2. Inside the tube (Fig. 2a) the spectrum is clearly dominated by argon lines. Only minor traces of molecular gases (300–360 nm) are also visible. This shows that although pure argon was used as the working gas, some small amount of air admixture was able to penetrate into the discharge inside the tube, either from impurities in gas pipes or by back diffusion from the open end of the tube. Nevertheless, their amount is negligible when compared to the intensity of argon lines. Outside the tube (Fig. 2b) the overall emissions are much weaker
and due to mixing with surrounding air, many other spectral features in addition to those of argon are present in the spectrum and share the dominant role with argon emissions. The most intense of these are molecular bands corresponding to excited OH molecules and nitrogen containing molecules (N2, NH, NO), and atomic lines of oxygen (777 nm) and hydrogen (656 nm). Further attention will be paid to the spectral features that are highlighted by colour in Fig. 2b.