Peter Kopcansky

Efficient adsorbents and nanozyme-like materials are of growing importance in environmental technologies. Here, we report a simple and potentially scalable approach for the immobilization of biochars onto nonwoven acrylic textiles, yielding composite materials with good retention of immobilized biochar during aqueous treatment and combined adsorption and peroxidase-like activities. The structure of native and biochar-modified textiles was characterized by scanning electron microscopy and small-angle X-ray scattering, confirming the presence of biochar particles on fiber surfaces and within the inter-fiber space, as well as nanoscale structural changes induced by biochar incorporation. Textile-bound biochars exhibited peroxidase-like activity toward N,N-diethyl-p-phenylenediamine in the presence of hydrogen peroxide and enabled effective decolorization of methylene blue. Adsorption alone resulted in 61% dye removal after 240 min, while the combined adsorption-catalytic process achieved 74% decolorization. Modification of the textile-bound biochar with copper ions further enhanced the peroxidase-like activity, increasing dye removal to 85% under identical conditions. The optional incorporation of a magnetic iron wire allows facile magnetic handling of the composite. Owing to its low cost, simplicity of preparation, and dual functionality, the textile-bound biochar composite represents a promising proof-of-concept platform that may warrant further development for dye removal and related environmental applications.

The electro-optical behavior of and electric-field-induced structural changes in nematic liquid crystals (6CHBT and 5CB) doped with a low concentration (1 × 10⁻⁴) of Mn-doped zinc ferrite nanoparticles were investigated. Light transmission and surface acoustic wave attenuation techniques were employed to monitor structural responses under increasing and decreasing electric field modes, as well as after pulsed field application. The influence of nanoparticle morphology (rods, needles, and clusters) and particle size on the field-induced structural modifications was systematically evaluated. Shifts in the threshold electric field were observed. The results obtained from both experimental approaches were compared in terms of suspension stability and demonstrate the potential of these ferronematic systems for applications in sensors, smart materials, and information storage devices.

Endovascular brain delivery and magnetic retention of nanocapsules for improved focal delivery.

The effect of Mn-doped zinc ferrite nanoparticles at a low volume concentration (1 × 10⁻⁴) on structural changes in the nematic liquid crystals 6CHBT and 5CB, induced by weak magnetic fields, was investigated using surface acoustic wave (SAW) and light transmission (LT) techniques. Structural changes caused by the applied magnetic field, in both increasing and decreasing modes, as well as after pulsed changes, were examined by measuring the responses of SAW attenuation and LT using a linearly polarized laser beam. The influence of nanoparticle shape (rods, needles, and clusters) and temperature on the structural changes was investigated. A shift in the threshold field and the transition temperature was observed. In addition, the magnetic properties of the individual samples in powder form were examined using M–H curves, M–T curves, and XRD patterns. The results obtained from all measurements are compared, and the effectiveness of each technique, considering the influence of nanoparticle shape and suspension stability, was evaluated.

The rheological properties of nonpolar ferrofluids have been often studied under the action of an external magnetic or electric field. In this paper, we approach the problem conversely, and we aim to answer whether the ferrofluid shear flow affects the dielectric response. The ferrofluids are based on transformer oil and iron oxide nanoparticles stabilized with oleic acid. Basic physical characterization of the ferrofluids with three different nanoparticle concentrations is followed by experimental investigation of flow curves. Newtonian behavior of the ferrofluids is confirmed. The key experiment of this study consists of complex dielectric permittivity measurements in the frequency range from 20 Hz to 100 kHz at three different temperatures. In these measurements, the ferrofluids are sandwiched between two disk electrodes of a modular rheometer under the shear rates of 0, 10, 100, 500, and 1000s^{-1}. It is found that the low-frequency dielectric spectra of the ferrofluids exhibit a remarkable conductivity contribution leading to electrode polarization. Additional measurements of electrical conductivity and qualitative analysis of charge mobility in the ferrofluids are provided to understand the low-frequency dielectric relaxation. The results reveal that the slow dielectric relaxation is shear rate independent. The low-frequency dielectric spectra measured under the various shear rates exhibit constant behavior. The electric charge migrates across the shear flow velocity in the shear rate direction and the given rheological conditions do not affect its behavior. It is concluded that the electrical forces dominate the charge motion in the ferrofluids over the shear forces. The finding of the stable dielectric response of ferrofluids under the shear flow conditions supports the application of ferrofluids as dielectric media in electrical equipment with the presence of forced or natural convection.

Dielectric properties of native nonwoven textile as well as textile with bound biochar and multi-walled carbon nanotubes in the frequency range of 10 to 5·105 Hz and at the temperatures of 30 to 60 °C have been investigated. The capacity of native nonwoven textile has been shown to decrease with the temperature according to the Arrhenius law. The activation energy of the temperature dependence of the capacity has been estimated to be 0.09 eV. It has been demonstrated that regardless of the temperature, the frequency dependence of the resistance of the nonwoven textile can be described by two exponential functions. In the presence of bound biochar and multi-walled carbon nanotubes in the nonwoven textile, the conductivity current was 4 orders of magnitude greater than the bias current and increased with the temperature according to the Arrhenius law. The activation energy of the temperature dependence of the inverse resistance (an analogue of the conductivity for homogeneous samples with the same dimensions) has been estimated to be 0.19 eV for the samples with multi-walled carbon nanotubes and 0.62 eV for the samples with bound biochar.

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe₃O₄ nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe₃O₄ magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe₃O₄ with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

High-frequency components such as microprocessors, transistors, antennas, voltage-controlled oscillators, and many others generate a large amount of heat. In the absence of satisfactory cooling, these components may suffer damage or even destruction. Therefore, it is important to find effective ways to cool these components. A possible solution is to use oil-based magnetic fluids. Magnetic fluids contain magnetic particles dispersed in oil, and their properties, including viscosity, affect their cooling capabilities. Viscosity can be changed by adding various additives or by adjusting the concentration of magnetic particles. The advantage of using oil-based magnetic fluids for cooling is that they allow for precise dosing and control of the amount of fluid applied to the component, reducing thermal losses and increasing cooling efficiency. In addition, oil-based magnetic fluids can also act as a dielectric, reducing electrical noise and increasing electromagnetic compatibility with the components. Analyzing the heating rate of magnetic fluids consisting of mineral oils in an alternating magnetic field with a frequency of 500 kHz, we have shown the capability of controlling thermal losses by adjusting the viscosity of the carrier liquid.

A study on 5CB liquid crystal composites with SiO₂ nanoparticles and an additional commixture with Fe₃O₄ nanoparticles using light transmission and SAW measurements is presented. The prepared liquid crystal composites exhibited an interesting memory effect characterized by the hysteresis of both light transmission and SAW attenuation responses investigated in the nematic phase. While in the case of SiO₂ nanoparticles as dopants, the liquid crystal composite showed an improvement in the memory effect, the addition of Fe₃O₄ magnetic nanoparticles resulted in the memory effect decreasing. Additional studies showed a significant shift in both the threshold voltage and nematic–isotropic transition temperature. Measurements in the magnetic field confirmed the increasing memory effect according to that of pure 5CB. The properties of these composites could lead to a potential application for the fabrication of memory devices suitable for information storage.