Lubomír Lapčík

Plasma surface modification of polyethylene

Oxidative (oxygen and air) RF-plasma treatment of HDPE was found as an effective tool for improving wettability, as well as for increasing its surface micro-hardness. The latter plasmas generate wide range of reactive species in the system, which undergo consecutive chemical reactions, creating thus several oxygen based functionalities at the interface (carbonyl, carboxyl, ether, peroxide etc.) as were detected by ATR FTIR and XPS analysis. An increased negative surface charge of plasma treated polyethylene (PE) confirms the presence of functional ionogenic groups containing oxygen. Simultaneously, the vigorous increase of the surface roughness was found as a result of the successful plasma etching.

Photocatalytic hydroxylation of benzoic acid in aqueous titanium dioxide suspension

The photocatalytic hydroxylation of benzoic acid in aqueous TiO2 suspension is suggested as evidence for the generation of hydroxyl radicals in the H2O(l)—TiO2(s) system. The hydroxylation reaction was studied by UV spectroscopy and high performance liquid chromatography (HPLC). The experimental results are discussed in terms of the formal kinetic analysis and the aromatic carbon charges calculated by the INDO method.

Chemical bath deposition of cerium doped BiVO4

Abstract The preparation of Ce doped BiVO 4 coatings on glass, by the thermal treatment of aqueous solutions containing a bismuth (III) ethylenediaminetetra-acetate chelate, vanadium (V) and cerium (III) species, is described here. The influence of cerium content on the colour properties of the coating was investigated. The coatings consist on morphological well-defined particles forming dense monolayers.

The zeta potential of kaolin suspensions measured by electrophoresis and electroacoustics

The zeta potentials of kaolin dilute and concentrated suspensions were monitored using the techniques of electrophoresis and electroacoustics, respectively. The effect of addition of salt (KCl), a polymer material (Triton X-100), and an anionic surfactant (sodium dodecyl sulphate, SDS) on the suspension properties was investigated by electrophoresis. Electroacoustics was employed for the measurement of zeta potentials for the highest possible kaolin content in suspension and the effect of dilution. The effect of aging of a freshly prepared sample and kaolin isoelectric point was also studied. Using both techniques it was noted that there was no isoelectric point, just a maximum value in the magnitude of the kaolin suspension zeta potential. These maxima were observed also in the presence of Triton X-100 and SDS. An increase of the concentration of KCl and SDS in suspension shifted the maxima towards more acidic values, while in the presence of Triton X-100 the position of the zeta potential maxima remained constant. Electroacoustic techniques revealed that a freshly prepared concentrated suspension requires about six hours to equilibrate to achieve a steady zeta potential. Diluting the concentrated suspensions led to decrease of the zeta potential as ions bound to the surface desorbed and screened the surface charge. The zeta potential maxima remained unchanged even after heating the powder in an oven at 200°C (to remove any organic material) thereby suggesting that the most likely explanation for the maxima is isomorphic substitution.

Photochemical degradation of hyaluronic acid by singlet oxygen

Changes of the rheological properties of hyaluronic acid (sodium-magnesium salt) solutions after exposure to UV radiation indicate a vigorous decrease in their viscosity, but its still strong shear rate dependence. Whereas the presence of the singlet oxygen sensitizer (anthracene-1-sulphonic acid) brings about a loss of shear dependence; the studied solutions show newtonian behavior.

ELECTRON PARAMAGNETIC RESONANCE STUDY OF FREE-RADICAL KINETICS IN ULTRAVIOLET-LIGHT CURED DIMETHACRYLATE COPOLYMERS

A spin-trapping technique and direct kinetic measurements of electron paramagnetic resonance spectra were used to investigate the kinetics of radical production in the cross-linking photo-initiator system based on camphoroquinone and dimethyl-aminoethylmethacrylate in the presence of the corresponding monomer dimethacrylate copolymer mixture, as well as in the pure photo-initiator system. Consequently, in both cases, the kinetics of radical production and decay was measured. From the measured data the formal kinetic parameters of particular radical processes were calculated by the non-linear least-squares regression method.

Chemical Modification of Hyaluronic Acid: Alkylation

Hydrophobically modified derivatives of hyaluronic acid (HA) are characterized by means of differential scaning calorimetry (DSC) measurements. Simultaneously, viscosity and elasticity are monitored by rheological measurements. Alkylation of HA macromolecule brings about a strong change in the rheological properties of the biopolymer, which leads to the succesful micelle formation process. The latter then create a highly organized supramolecular structure in the solution, which at the length of the alkyl chain of C15 and higher, is characterized by the creation of the isotropic liquid crystal phase transition.

Influence of artificially accelerated ageing on the adhesive joint of plasma treated polymer materials

An influence of simulated ageing on the adhesive joint of plasma treated polyethylene (PE) and polypropylene (PP) was tested. Plasma surface treatment was performed in the rf-plasma reactor operating at 13,56 MHz. The simulated ageing of prepared specimens for following tensile testing was carried out under conditions given by Volkswagen standard P-VW 1200. Temperature of ageing was regularly oscillating between −40°C and 80°C (relative humidity 80%) for required time. The mechanical tensile properties of adhesive joint were measured according to the standard ISO 527. Surface analysis of treated polymer substrates was characterized by XPS measurement. The observation of surface structure and morphology was obtained using SEM. We used convenient cyanoacrylate adhesive Loctite E 406 for PE and PP joints. Tested adhesive joints were prepared in compliance with the standard ISO 4587.

Photocatalytic degradation of hydroxyethylcellulose in aqueous PtTiO2 suspension

Abstract The photocatalytic degradation was studied of hydroxyethylcellulose (HEC) in an aqueous Ptue5f8TiO2 suspension in the presence of oxygen using medium pressure mercury lamp radiation with a Pyrex sleeve. The viscosity of the HEC solution decreased significantly and the evolution of carbon dioxide was found during irradiation. The degree of polymerization of the HEC changed rapidly (especially in the initial reaction stages). The molecular size distribution of the irradiated HEC was studied by high performance liquid chromatography. Similar effects were observed during solar irradiation of HEC in aqueous Ptue5f8TiO2 suspension. The mechanism of photocatalytic degradation of HEC is suggested.

Effect of Low Temperature Air Plasma Treatment on Wetting and Flow Properties of Kaolinite Powders

It was found in this study that the air plasma treatment of particular kaolinite has led to the change of its wettability, which was reflected in the decreased values of water contact angles of wetting from 88.7° for virgin kaolinite to 86.3° for 30xa0min air plasma treated one. Plasma treated samples show higher average surface energies in the wide range of coverage regimes in comparison to the virgin samples as determined by inverse gas chromatography. Results of these measurements confirmed our assumption, that air plasma treatment activates surface energy of the crystal planes of the kaolinite as reflected in the broadened dispersive surface energy distribution after 10xa0min treatment time. However with prolonged 30xa0min treatment time the dispersive surface energy distribution profile was decreased. We assume, that the latter decrease reflects the distorsion of the crystal lattice of the kaolinite as confirmed by FTIR analysis as reflected in changes of Si–O–Si and Al2O–H characteristic absorption bands. Calculated dispersive surface free energy for 24xa0% surface coverage was increased from original 35xa0mJ/m2 to 40.3 and 40.8xa0mJ/m2 for 10 and 30xa0min treatment times. There were determined yield locus and flow function dependencies at different stress levels for virgin and different time plasma treated samples (flow index—ffc, effective angle of internal friction—φe, unconfined yield strength—σc). It was found that by plasma treatment the character of the flow was shifting from region of very cohesive (ffcxa0=xa02.39) to the cohesive (ffcxa0=xa03.19). For untreated samples effective angle of internal friction was decreased with increasing applied consolidation stress, while for plasma treated kaolinite it was increased.