Miroslav Pastorek

The formation mechanism of iron oxide nanoparticles within the microwave-assisted solvothermal synthesis and its correlation with the structural and magnetic properties

Magnetic nanoparticles based on Fe3O4 were prepared by a facile and rapid one-pot solvothermal synthesis using FeCl3·6H2O as a source of iron ions, ethylene glycol as a solvent and NH4Ac, (NH4)2CO3, NH4HCO3 or aqueous NH3 as precipitating and nucleating agents. In contrast to previous reports we reduce the synthesis time to 30 minutes using a pressurized microwave reactor without the requirement of further post-treatments such as calcination. Dramatically reduced synthesis time prevents particle growth via Ostwald ripening thus the obtained particles have dimensions in the range of 20 to 130 nm, they are uniform in shape and exhibit magnetic properties with saturation magnetization ranging from 8 to 76 emu g(-1). The suggested method allows simple particle size and crystallinity tuning resulting in improved magnetic properties by changing the synthesis parameters, i.e. temperature and nucleating agents. Moreover, efficiency of conversion of raw material into the product is almost 100%.

Characterization of Antibacterial, Mechanical, and Structural Properties of Polyvinyl Chloride/Silver Nitrate Composites Prepared by Thermoplastic Compounding

Polyvinyl chloride/silver nitrate composites were prepared by thermoplastic compounding. Antibacterial activity against gram-negative and gram-positive bacteria was determined by agar diffusion test. X-ray diffraction, X-ray photoelectron spectroscopy, and optical microscopy analyses were carried out to determine the effect of polyvinyl chloride modification on structural properties. The mechanical characteristics of prepared films were observed using stress-strain analysis. The results revealed that final composites exhibit sufficient antibacterial properties against tested bacteria, with nonuniform distribution of silver particles in the PVC matrix, which caused a decrease in mechanical properties. X-ray characterization proved the presence of the modifier, mostly in Ag+ form.

Magnetic Iron Oxide Nanoparticles for High Frequency Applications

Magnetic properties of iron oxide nanoparticles synthesized by microwave solvothermal method are reported. The effect of the nucleating agent on the composition, size, morphology and microstructure of nanoparticles was studied with a view to their correlation with magnetic properties. It is shown that a soft magnetic material with high value of magnetization saturation and high-frequency dispersion of complex permeability can be obtained by an appropriate choice of the nucleating agent.

Effects of thermal annealing as polymer processing step on poly(lactic acid)

ABSTRACT Thermal annealing as an additional polymer processing step or post-treatment processing step enables the structural changes of amorphous parts into crystalline parts. This paper investigates the feasibility of thermal annealing at 100°C up to 90 min used as an additional processing step to modify the crystalline structure and the thermo-mechanical stability of poly(lactic acid) (PLA). Moreover, the crystallization ability of PLA has been amended by the addition of 3 wt% of wood flour and kaolin. The values of the degree of crystallinity and lamellar thickness determined by wide-angle-X-ray scattering showed that the thermal annealing of PLA samples modified with nucleating agents was an efficient processing step to increase the final crystallinity of PLA. Moreover, altered crystalline structure helped to improve the thermomechanical stability of PLA.

Heating Efficiency of Iron Oxide Nanoparticles in Hyperthermia: Effect of Preparation Conditions

The correlation between magneto-structural properties of iron oxide nanoparticles and their heating efficiency in ac magnetic fields is investigated. Nanoparticles with an average size of 13 nm and narrow size distribution are synthesized by coprecipitation of ferrous and ferric salts in an alkaline medium in which the salts ratio is systematically varied. To obtain nanoparticles with single-phase composition, the prepared samples are annealed at 200 °C. The lattice parameters of all nanoparticles deduced from X-ray diffraction analysis correspond to multiphase composition, i.e., to a mixture of magnetite and maghemite phases. However, low-temperature Mossbauer spectroscopy revealed complete transformation of magnetite to maghemite in annealed samples. The annealed samples show slightly higher value of specific loss power at a certain frequency and amplitude of ac magnetic field compared with other samples.

Effect of hydrothermal treatment on the structure of an aluminosilicate polymer

AbstractThe effect of hydrothermal treatment on the structure of an aluminosilicate polymer prepared by a polycondensation reaction between silicate and hydroxoaluminate in alkaline aqueous solution was studied. The structural changes were investigated using X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy imaging and thermogravimetric analysis. The results indicated that the amorphous aluminosilicate polymer transformed into a crystalline product during the hydrothermal treatment at 145°C. The crystalline phase was identified as a mineral of the zeolite group, most likely phillipsite. This transformation required an alkaline environment during the hydrothermal treatment.

Crosslinking and ageing of ethylene-vinyl silane copolymer in water bath

The paper focuses on chemical and morphological changes of ethylene-vinyl silane copolymer upon exposure to hot water. Within processing, the exposure to hot water is the final step causing crosslinking and stabilization of material against high temperatures, which can occur in application to wire insulation. For these purposes, commercially available copolymer and catalytic system have been used. A strong effect of catalytic system on kinetics of crosslinking and subsequently ageing was observed. Chemical evolution was followed by infrared spectroscopy and differential scanning calorimetry was involved for evaluation of morphological changes.