Alena Juríková

Structure of water-based ferrofluids with sodium oleate and polyethylene glycol stabilization by small-angle neutron scattering: contrast-variation experiments

Contrast variation in small-angle neutron scattering (SANS) experiments is used to compare the structures of a water-based ferrofluid, where magnetite nanoparticles are stabilized by sodium oleate, and its mixture with biocompatible polyethylene glycol, PEG. The basic functions approach is applied, which takes into account the effects of polydispersity and magnetic scattering. Different types of stable aggregates of colloidal particles are revealed in both fluids. The addition of PEG results in a reorganization of the structure of the aggregates: the initial comparatively small and compact aggregates (about 40 nm in size) are replaced by large (more than 120 nm in size) fractal-type structures. It is postulated that these large structures are composed of single magnetite particles coated with PEG, which replaces sodium oleate. Micelle formation involving free sodium oleate is observed in both fluids. The structures of the fluids remain unchanged with increasing temperature up to 343 K. New and specific possibilities of SANS contrast variation with respect to multicomponent systems with different aggregates are considered.

Thermal Properties of Magnetic Nanoparticles Modified With Polyethylene Glycol

Magnetic fluids used in biomedicine have to be biocompatible and therefore the magnetic nanoparticles are modified by different biocompatible materials. In this work the magnetic nanoparticles Fe3O4 sterically stabilized by sodium oleate were prepared by coprecipitation method. Consequently they were modified with polyethylene glycol (PEG) of different molecular weights and different PEG to magnetite Fe3O4 feed weight ratios varying from 0.01 to 30 to produce biocompatible magnetic fluids (MFPEG). The morphology was observed by scanning electron microscopy. The magnetic nanoparticles coated with PEG showed almost spherical shape for all studied systems of MFPEG. Differential scanning calorimetry (DSC) was used to study the adsorption of PEG on magnetic nanoparticles and to determine the maximal amount of PEG adsorbed on the magnetic nanoparticles. The increasing PEG molecular weight leads to the decrease in maximal PEG/Fe3O4 feed weight ratio. In vitro toxicity of the magnetic fluids using cells of skin cancer of mice B16 was tested with the aim to confirm the biocompatibility of the prepared magnetic fluids.

Magnetic polymer nanospheres for anticancer drug targeting

Poly(D,L-lactide-co-glycolide) polymer (PLGA) nanospheres loaded with biocom-patible magnetic fluid as a magnetic carrier and anticancer drug Taxol were prepared by the modified nanoprecipitation method with size of 200–250 nm in diameter. The PLGA polymer was utilized as a capsulation material due to its biodegradability and biocompatibility. Taxol as an important anticancer drug was chosen for its significant role against a wide range of tumours. Thermal properties of the drug-polymer system were characterized using thermal analysis methods. It was determined the solubility of Taxol in PLGA nanospheres. Magnetic properties investigated using SQUID magnetometry showed superparamagnetism of the prepared magnetic polymer nanospheres.

Nanoindentation Study of the Influence of the Loading Rate on the Deformation of Metallic Glasses

Nanoindentation experiments at the loading rates from 0.05 to 100 mN.s-1 on the amorphous FeNiB alloy were executed. We found that the serrations in the load-displacement (P-h) curve are more pronounced at lower loading rates and gradually disappear upon increasing loading rate. We have estimated the contribution of the inhomogeneous plastic deformation from pop-in events on the P-h curves. The pop-in population was compared with the morphology of indents.

Nanocrystallization of Finemet alloy after intensive plastic deformation

The Finemet alloy prepared by the crystallizaton of an amorphous precursor is a basic model material for study of magnetic nanoparticle structures. It was shown that intensive plastic deformation localized into adiabatic shear bands causes intensive heating and structural changes in the amorphous alloy. These changes influence the magnetic properties of the amorphous precursor and the Finemet crystallization. Direct creep measurements during the crystallization of Finemet alloys were performed and the creep properties of the residual amorphous phase formed during the nanocrystallization were described. It was shown that due to relatively high temperatures the residual amorphous phase undergoes intensive structural relaxation resulting in the obvious embrittlement of these materials.

Serrated Plastic Flow of Various Metallic Glasses during Nanoindentation

Nanoindentation experiments were executed on amorphous metallic ribbons made of Fe40Ni40B20, Cu47Ti35Zr11Ni6Si1 and Zr65Cu17.5Ni10Al7.5 that differ in microhardness and glass forming ability. The individual serrated plastic flow events were analyzed in a wide range of the loading rates. In the individual pop-in events of the load-displacement (P-h) curve the contributions of plastic deformation (Δhpl) were calculated depending on the loading rate and the alloy composition. It is concluded that the contribution of the serrated plastic deformation flow varies with the composition of the alloy. The highest plastic deformation for the individual pop-ins was observed for Zr-based metallic glasses.

Degradation of BSA Coating on Magnetite Nanoparticles

Magnetic nanoparticles used in biomedicine have to be biocompatible what can be achieved by the modification of the magnetic particle surface with an appropriate biocompatible substance. In the work protein bovine serum albumin (BSA) was chosen to modify the surface of magnetite nanoparticles. BSA coated magnetite nanoparticles (MFBSA) with different feed weight ratios of BSA to the magnetite Fe3O4 were prepared and thermally characterized using thermogravimetric analysis.

Creep strain recovery of Fe-Ni-B amorphous metallic ribbon

Creep strain recovery and structural relaxation of the amorphous metallic glass Fe40Ni41B19 after longtime loading at different annealing temperatures below the glass transition temperature have been studied using anisothermal differential scanning calorimetry (DSC) and dilatometry (TMA). It has been demonstrated that structural relaxation effects depend on the stress-annealing temperature of the amorphous ribbon. The structural relaxation states of the amorphous ribbon annealed at different temperatures under and without applied stress have been compared. The activation energy spectra were calculated from the anisothermal dilatometric measurements using the modern method based on the Fourier transformation technique. The influence of the annealing temperature on the shape of creep strain recovery spectra has been analyzed.

Tuning the phase transition temperature of ferronematics with a magnetic field

The influence of magnetic field on the isotropic-to-nematic phase transition temperature is investigated in neat bent-core and calamitic liquid crystals, in their mixture, and in samples doped with spherical magnetic nanoparticles for two different orientations of the magnetic field. A magnetic-field-induced negative or positive shift of the transition temperature was detected depending on the magnetic field orientation with respect to the initial orientation of the nematic phase, and on the type of liquid crystal matrix.

Deformation and Failure of Ultrafine-Grained Cu at Subambient Temperature

The ultrafine-grained copper was obtained by 12 passes of equal-channel angular pressing method. The uniaxial tensile tests at room temperature and the subambient temperature of 77 K show that the yield stress increases from the value of 128 MPa to the value of 138 MPa, respectively. In addition, the lowering the test temperature tends to the increase of the deformation before the failure. The fractographic analysis shows the transcrystalline ductile failure for all samples. Due to the high plasticity of nanostructured copper no influence of the nanoporosity on the failure process was observed.