Tomáš Morávek

Fluorescence (TALIF) measurement of atomic hydrogen concentration in a coplanar surface dielectric barrier discharge

Spatially and temporally resolved measurements of atomic hydrogen concentration above the dielectric of coplanar barrier discharge are presented for atmospheric pressure in 2.2% H2/Ar. The measurements were carried out in the afterglow phase by means of two-photon absorption laser-induced fluorescence (TALIF). The difficulties of employing the TALIF technique in close proximity to the dielectric surface wall were successfully addressed by taking measurements on a suitable convexly curved dielectric barrier, and by proper mathematical treatment of parasitic signals from laser–surface interactions. It was found that the maximum atomic hydrogen concentration is situated closest to the dielectric wall from which it gradually decays. The maximum absolute concentration was more than 1022 m−3. In the afterglow phase, the concentration of atomic hydrogen above the dielectric surface stays constant for a considerable time (10 μs–1 ms), with longer times for areas situated farther from the dielectric surface. The existence of such a temporal plateau was explained by the presented 1D model: the recombination losses of atomic hydrogen farther from the dielectric surface are compensated by the diffusion of atomic hydrogen from regions close to the dielectric surface. The fact that a temporal plateau exists even closest to the dielectric surface suggests that the dielectric surface acts as a source of atomic hydrogen in the afterglow phase.

Coplanar Dielectric Barrier Discharge on a High-Permittivity Dielectric Surface

Coplanar barrier discharge with concentric electrode configuration was used to study the processes affecting the mutual interactions of individual discharge microfilaments. To elucidate the role of surface charge on the dielectrics, discharge characteristics on various coatings with different permittivity have been investigated. Owing to the thermo-chemical erosion of the coating with particularly high-permittivity (εr = 12000) a novel regime of discharge appearance is observed, consisting of micro-plasma spots filling the pores in high-ε dielectric created by the action of initial microfilaments and bright, extended length plasma channels arching over the interelectrode space. A visual record of this phenomenon is presented.

Nonthermal plasma modification of polypropylene fibres for cementitious composites

Abstract The plasma treatment of polypropylene fibres used as concrete admixtures for improving its mechanical properties is the focus of this research paper. A plasma treatment was conducted in a low-temperature plasma environment at atmospheric pressure in a DCSBD (Diffuse Coplanar Surface Barrier Discharge). The degree of hydrophilicity caused by the plasma treatment was determined by measuring the rate of penetration of water into the porous media, commonly referred to as the Washburn method. The influence of the addition of PP (polypropylene) fibres to the concrete matrix was investigated using a three point bending test which determined the flexural strength of concrete samples. Our experiments demostrate that plasma improves both the wettability of PP fibres and its adhesion to the concrete matrix. The tests of flexural strength show, that even a short plasma treatment (5 s) can have a significant impact on the mechanical properties of fibre-reinforced concrete composite. Graphical Abstract

Surface Morphology Study on Fibres Treated in Cold Plasma Discharge

The paper presents results related to surface treatment of polypropylene fibres with intention to increase its performance in cement composite by exposing such fibres in cold plasma discharge. In was previously demonstrated that such treatment has beneficial effect. Here we focused mainly on the changes in the surface. The study was carried out by electron microscopy, confocal microscopy and microscopy of atomic forces. The results suggest increasing degree of change in the surface as the energy of discharge and time of exposure increase. Atomic force microscopy indicates increase in adhesion force.