Jozef Ráheľ

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.

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

DBD Plasma Assisted Silver Functionalization of Surgical Meshes

Atmospheric pressure diffuse barrier discharge in nitrogen was employed to promote the formation sub-micron particles of silver salts of AgNO3, Ag2O, Ag2CO3 and AgCl on polypropylene and polyester warp-knitted surgical meshes. The methods for producing and evaluation of coating are described in detail. All silver salts proved their antimicrobial efficacy against gram-positive S. aureus and gram-negative E. coli. In general the quantity of immobilized silver sufficient for antibacterial action was found to be in the order of units of mg per gram of polymer mesh.

The Evaluation of Modifications to Glued Joints Utilizing Epoxy-Based Adhesive for Structural Timber Bonding

The behavior of two types of modifications to glued joints utilizing epoxy resin-based adhesive was examined in a manner specified by the EN 302 standard using adherent beech wood specimens. The investigation was focused on the improvement of glued joint strength and adhesive properties. The first type of modification involved reinforcement of the epoxy-based adhesive with scattered polypropylene fibers with the aim of enhancing the tensile shear strength of the assembly. The other type of glued joint modification was the electrical discharge plasma treatment of the adherend surface. This technique for treating the surfaces of materials enables the greater spreading of liquids due to the increase in surface wettability it provides. Relevant characteristics of the test specimen – tensile shear strength and wood failure - were tested in order to analyze the behavior of the thus-modified epoxy-based adhesive-glued joints.