Natalia Tomasovicova - Academia.edu (original) (raw)

Papers by Natalia Tomasovicova

Soft Matter, 2016

Magnetic properties of a ferronematic, i.e., nematic liquid crystal doped with magnetic nanoparti... more Magnetic properties of a ferronematic, i.e., nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (units of Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase). These experimental findings pave a way to application possibilities, such as low magnetic field sensors, or basic logical elements for information storage.

Acta Physica Polonica A, 2008

In this work we describe the magnetic Freedericksz transition in HABbased (4,4-din -heptylazoxybe... more In this work we describe the magnetic Freedericksz transition in HABbased (4,4-din -heptylazoxybenzene) ferronematics. The ferronematic samples were prepared with two different volume concentrations of magnetic particles φ 1 = 2 × 10 −5 and φ 2 = 2 × 10 −4. The liquid crystal HAB is nematic at the temperatures from ≈ 53 • C to 70 • C and smectic A at the temperatures under 53 • C. The anisotropy of dielectric permitivity of HAB liquid crystal is positive in nematic phase and negative in smectic A phase. The magnetic Fredericksz transition was studied in nematic phase at temperature 60 • C.

Acta Physica Polonica A, 2010

The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter ... more The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter 3-5 nm) on the structural transitions was investigated. The studied samples were based on the nematic liquid crystal 4-(trans-4-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The volume concentration of the gold particles was φ 1 = 2 × 10 −4 and φ 2 = 10 −3. The obtained results showed that the inclusion of the gold particles in the 6CHBT liquid crystal increases the sensitivity of such system on the external magnetic field.

physica status solidi (b), 2008

The spin-one-half Falicov-Kimball model with spin-dependent on-site interaction between localized... more The spin-one-half Falicov-Kimball model with spin-dependent on-site interaction between localized (f) and itinerant (d) electrons is studied by smallcluster exact-diagonalization calculations and a well-controlled approximative method in two dimensions. The results obtained are used to categorize the ground-state configurations according to common features (charge and spin ordering) for all f and d electron concentrations (n f and n d) on finite square lattices. It is shown that only a few configuration types form the basic structure of the charge phase diagram in the n f − n d plane. In particular, the largest regions of stability correspond to the phase segregated configurations, the axial striped configurations and configurations that can be considered as mixtures of chessboard configurations and the full (empty) lattice. Since the magnetic phase diagram is much richer than the charge phase diagram, the magnetic superstructures are examined only at selected values of f and d electron concentrations.

International Journal of Thermophysics, 2007

This work is devoted to the study of heating of biocompatible magnetic fluid due to time-varying ... more This work is devoted to the study of heating of biocompatible magnetic fluid due to time-varying magnetic induction. The adsorption of dextran on magnetite particles was confirmed by IR spectroscopy. A considerable thickness of the surfactant layer (oleate sodium + dextran) of about 4.3 nm prevents the formation of clusters made of nanomagnetic particles as evidenced by the fact that no maxima of ultrasound wave absorption coefficient corresponding to cluster formation have been detected. The results show that observed heating effect may be applied in hyperthermia treatments especially in preferable region 500-800 kHz. A "H 2-law" observed for the dependence of the SAR on the square amplitude of the magnetic field testify about presence superparamagnetic particles in the ferrofluid.

Nanoscale Advances, 2021

The interplay between the anchoring of liquid crystal (LC) molecules at the substrate and at the ... more The interplay between the anchoring of liquid crystal (LC) molecules at the substrate and at the surface of nanoparticles (NPs) results in an orientational self-assembly of nanoparticles in sessile nematic droplets.

arXiv: Soft Condensed Matter, 2010

The radiation stability of biocompatibile magnetic fluid used in nanomedicine after electron irra... more The radiation stability of biocompatibile magnetic fluid used in nanomedicine after electron irradiation was studied. Two types of the water-based magnetic fluids were prepared. The first one was based on the magnetite nanoparticles stabilized by one surfactant natrium oleate. The second one was biocompatibile magnetic fluid stabilized with two surfactants, natrium oleate as a first surfactant and Poly(ethylene glycol) (PEG) as a second surfactant. The magnetization measurements showed that electron irradiation up to 1000Gy caused 50% reduction of saturation magnetization in the case of the first sample with only one surfactant while in the case of the second biocompatibile magnetic fluid, only 25% reduction of saturation magnetization was observed. In the first magnetic fluid the radiation caused the higher sedimentation of the magnetic particles than in the second case, when magnetic particles are covered also with PEG. The obtained results show that PEG behave as a protective ele...

Molecules, 2021

Understanding the formation process and the spatial distribution of nanoparticle (NP) clusters on... more Understanding the formation process and the spatial distribution of nanoparticle (NP) clusters on amyloid fibrils is an essential step for the development of NP-based methods to inhibit aggregation of amyloidal proteins or reverse the assembling trend of the proto-fibrillary complexes that prompts pathogenesis of neuro degeneration. For this, a detailed structural determination of the diverse hybrid assemblies that are forming is needed, which can be achieved by advanced X-ray scattering techniques. Using a combined solution small angle X-ray scattering (SAXS) and atomic force microscopy (AFM) approach, this study investigates the intrinsic trends of the interaction between lysozyme amyloid fibrils (LAFs) and Fe3O4 NPs before and after fibrillization at nanometer resolution. AFM images reveal that the number of NP clusters interacting with the lysozyme fibers does not increase significantly with NP volume concentration, suggesting a saturation in NP aggregation on the fibrillary sur...

Liquid crystals (LCs) composed of mesogens play important roles in various scientific and enginee... more Liquid crystals (LCs) composed of mesogens play important roles in various scientific and engineering problems. How a system with many mesogens can enter a LC state is an interesting and important problem. Using stiff and free-joint Lennard-Jones chain molecules as mesogens, we study the conditions under which the mesogens can enter various LC phases. The guideline is to eliminate the unwanted translational orders under a controlled fine-tuning procedure across a sequence of systems. Instead of monitoring the growth of order out of the disorder, we prepare a configuration of high orientation ordering and find out where it relaxes to. Such a procedure begins with a reference system, consisting of short chains of homogeneous soft spheres, in a liquid-vapor coexistence situation, at which the thermodynamic instability triggers a fast spontaneous growing process. By applying a short pulse of auxiliary field to align the dispersedly oriented clusters, followed by reducing the volume and,...

The presented chapter provides an overview of selected magnetic nanoparticle systems (magnetic fl... more The presented chapter provides an overview of selected magnetic nanoparticle systems (magnetic fluids, magnetosomes, magnetoferritin and liquid crystals doped with magnetic particles) as the unique materials with potential utilization in the field of biological and biomedical applications as well as in the field of technology. The main idea for magnetic nanoparticles incorporating is the improvement of material properties and to achieve better conditions for a wide range of scientific disciplines such as magnetic hyperthermia, drug delivery, magneto-optics, power engineering and others.

Nanomaterials

This research study attempts to prove the concept of the applicability of hyperthermia to treatin... more This research study attempts to prove the concept of the applicability of hyperthermia to treating the lysozyme amyloid fibrils (LAFs)’s self-assembled fibrillary aggregates by a feedback-modulated temperature controller ranging from 26 °C to 80 °C, and separately, by near-infrared (NIR) laser-irradiated cesium tungstate (CsWO3) nanoparticle (NPs). The dependence of the final morphology of the amyloidal assembly on external heating and the photothermal effect of the NPs on treating the fibrillary assembly were investigated and analyzed. Experimentally, atomic force microscopy (AFM), optical stereoscopy, and scanning electron microscopy (SEM) were used primarily to ensure mutual interaction between LAFs and NPs, optically elucidate the surface contour and final fibrillary assembly upon the influence of thermal treatment, and further reveal fine-details of the optical samples. Finally, conclusive remarks are drawn that the fibrillary structures doped with the NPs exhibit an increasing...

Colloids and surfaces. B, Biointerfaces, 2018

In this research, the dynamic process of aggregation that forms microflower morphology in solutio... more In this research, the dynamic process of aggregation that forms microflower morphology in solution of lysozyme amyloid fibrils doped with spherical or spindle-like magnetic nanoparticles during the process of drying as well as their final microstructures were investigated. The prepared lysozyme amyloid fibrils as well as their mixtures with in-lab synthesized magnetic particles, which were prepared by adding the nanoparticles to the fibrils solution after the process of fibrillation was done, were characterized using brightfield trans-illumination-mode optical microscope, atomic force microscopy (AFM) and scanning electron microscope (SEM). Brightfield optical imaging bases upon photoabsorptive property of the fibrils-nanoparticle composites clearly reveals the morphological features in microscale, and additionally, for the in vivo, live action of the time-dependent process of self-assembly of such composites composed of fibrillary structure incorporated with magnetic particles was ...

Soft Matter

This work is devoted to the study of highly stable composite systems of the liquid crystal 4-n-pe... more This work is devoted to the study of highly stable composite systems of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) doped with CoFe2O4 magnetic nanoparticles. The ferronematic samples were prepared with the...

Acta Physica Polonica A, 2012

The magnetic particles in the water-based magnetic uids were sterically stabilized by natrium ole... more The magnetic particles in the water-based magnetic uids were sterically stabilized by natrium oleate to prevent their agglomeration and consequently the adsorption of poly-ethylene-glycol (PEG) was carried out to improve the biocompatibility of the magnetic particles. Two sets of samples were prepared. The rst set of the samples was with dierent molar weight of PEG (Mw = 400, 1000, 10 000 and 20 000) at the constant weight ratio of PEG/Fe3O4 = 0.25 and the second one was with dierent weight ratio of PEG/Fe3O4 and constant molar weight of PEG (Mw = 1000). The samples were irradiated with 20 Gy. The same reduction of saturated magnetization (about 10%) after electron irradiation with 20 Gy was observed for all prepared samples.

Neuro Endocrinology Letters, 2006

Magnetic rod-like particles have been prepared through two type hydrolysis. The influence of diff... more Magnetic rod-like particles have been prepared through two type hydrolysis. The influence of different conditions during synthesis on the size (length and diameter), structure and magnetic properties of the prepared nanoparticles was studied. The molar ratio of the reactants affects structure, shape and magnetic properties of particles. The prepared samples were characterized by a variety of methods: infrared spectroscopy, magnetization measurements, Transmission electron microscopy and Scanning electron microscopy.

Liquid Crystals

We have investigated the influence of doping with spherical magnetic nanoparticles on the mixture... more We have investigated the influence of doping with spherical magnetic nanoparticles on the mixture of a bent-core and a calamitic liquid crystal. Results showed a reduction of the critical field of the magnetic Fréedericksz transition by more than a factor of two after the doping. Moreover, we give for the first time experimental evidence of the theoretically predicted magnetically induced negative shift of the isotropic to nematic phase transition temperature.

Physical Review E, 2008

In this work the 4-͑trans-4Ј-n-hexylcyclohexyl͒-isothiocyanatobenzene ͑6CHBT͒ liquid crystal was ... more In this work the 4-͑trans-4Ј-n-hexylcyclohexyl͒-isothiocyanatobenzene ͑6CHBT͒ liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements and showed significant influence of the shape and size of the magnetic particles on the magnetic Fréedericksz transition. For the volume concentration =2ϫ 10 −4 of the magnetic particles, the critical magnetic field was established for the pure liquid crystal, and for liquid crystals doped with spherical, chainlike, and rodlike magnetic particles. The influence of the magnetic field depends on the type of anchoring, which is characterized by the density of anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. The experimental results indicated soft anchoring in the case of spherical magnetic particles and rigid anchoring in the case of rodlike and chainlike magnetic particles, with parallel initial orientation between the magnetic moments of the magnetic particles and director.