Z. Mitróová

Capacitance changes in ferronematic liquid crystals induced by low magnetic fields

The response in capacitance to low external magnetic fields (up to 0.1 T) of suspensions of spherical magnetic nanoparticles, single-wall carbon nanotubes (SWCNT), SWCNT functionalized with carboxyl group (SWCNT-COOH) and SWCNT functionalized with Fe3O4 nanoparticles in a nematic liquid crystal has been studied experimentally. The volume concentration of nanoparticles was φ1 = 10 −4 and φ2 = 10 . Independent of the type and the volume concentration of the nanoparticles, a linear response to low magnetic fields (far below the magnetic Fréederiksz transition threshold) has been observed, which is not present in the undoped nematic. PACS numbers: 61.30.Gd, 77.84Nh, 75.50.Mm, 75.30.Gw ∗ Corresponding author; tothkatona.tibor@wigner.mta.hu

SANS contrast variation study of magnetoferritin structure at various iron loading

Abstract Magnetoferritin, a synthetic derivate of iron storage protein – ferritin, has been synthesized with different iron oxide loading values. Small-angle neutron scattering experiments were applied to study the structure of magnetoferritin solutions using contrast variation method by varying the light to heavy water ratio of the solvent. Higher iron loading leads to increase of the neutron scattering length density of magnetoferritin and also to the increase of the polydispersity of complexes. The formation of the magnetic core and the variation of the protein shell structure upon iron loading are concluded.

High concentration ferronematics in low magnetic fields

Abstract We investigated experimentally the magneto-optical and dielectric properties of magnetic-nanoparticle-doped nematic liquid crystals (ferronematics). Our studies focus on the effect of the very small orienting bias magnetic field B bias , and that of the nematic director pretilt at the boundary surfaces in our systems sensitive to low magnetic fields. Based on the results we assert that B bias is not necessarily required for a detectable response to low magnetic fields, and that the initial pretilt, as well as the aggregation of the nanoparticles play an important (though not yet explored enough) role.

Morphology and Magnetic Structure of the Ferritin Core during Iron Loading and Release by Magnetooptical and NMR Methods

Ferritins are proteins, which serve as a storage and transportation capsule for iron inside living organisms. Continuously charging the proteins with iron and releasing it from the ferritin is necessary to assure proper management of these important ions within the organism. On the other hand, synthetic ferritins have great potential for biomedical and technological applications. In this work, the behavior of ferritin during the processes of iron loading and release was examined using multiplicity of the experimental technique. The quality of the proteins shell was monitored using circular dichroism, whereas the average size and its distribution were estimated from dynamic light scattering and transmission electron microscopy images, respectively. Because of the magnetic behavior of the iron mineral, a number of magnetooptical methods were used to gain information on the iron core of the ferritin. Faraday rotation and magnetic linear birefringence studies provide evidence that the iron loading and the iron-release processes are not symmetrical. The spatial organization of the mineral within the proteins core changes depending on whether the iron was incorporated into or removed from the ferritins shell. Magnetic optical rotatory dispersion spectra exclude the contribution of the Fe(II)-composed mineral, whereas joined magnetooptical and nuclear magnetic resonance results indicate that no mineral with high magnetization appear at any stage of the loading/release process. These findings suggest that the iron core of loaded/released ferritin consists of single-phase, that is, ferrihydrite. The presented results demonstrate the usefulness of emerging magnetooptical methods in biomedical research and applications.

SAW study of structural changes in liquid crystals doped with carbon nanotubes induced by electric and magnetic fields

The doping of liquid crystals (LCs) with carbon nanotubes and magnetic nanoparticles have attracted wide interest in many areas of science, technology and medicine. LCs occur as additional, thermodynamically stable states of matter between the liquid state and the crystal state in some materials. They can be characterized by a long-range orientational order of the molecules and, as a consequence, by an anisotropy in their physical properties. LCs can be oriented under electric or magnetic fields due to the anisotropy of dielectric permittivity or diamagnetic susceptibility. Carbon nanotubes are molecular scaled tubes of graphitic carbon with outstanding properties. The simplest nanotube is composed of a single sheet of a network of carbon atoms, called graphene, which is rolled up into a tubular form. Because of the small value of the anisotropy of the diamagnetic susceptibility of liquid crystals, the idea of doping them with fine magnetic particles was also introduced. Nanotubes can undergo functionalization, including by magnetic particles, to produce novel hybrid materials potentially suitable for applications.

Effects of non-additive conductivity variation for a nematic liquid crystal caused by magnetite and carbon nanotubes at various scales

ABSTRACT Effect of magnetite and single-walled carbon nanotubes (CNTs) on the electric conductivity of 6CHBT nematic liquid crystal (LC) dispersed in polyvinyl alcohol is studied. The chosen technology of mixture homogeneising is shown to result in a LC dispersed in a polymer matrix (PDLC) with average LC droplet size of 500 nm (nano-PDLC). The conductivity of the nano-PDLC films with simultaneously introduced magnetite and nanotubes is shown to be smaller than the sum of the conductivities of films with nanoparticles of each type introduced separately. The main reason for this effect is assumed to be the formation of deep electron trap levels from complexes of nanoparticles of different type and thereby a decrease of the electron conductivity across the polymer which is the main mechanism of charge transfer in nano-PDLC. The effect of magnetite and the CNTs on the conductivity of the homogeneous LC and the micro-PDLC is analysed in comparison with the nano-PDLC. GRAPHICAL ABSTRACT

DSC Study of Bent-Core and Rod-Shaped Liquid Crystal Mixtures

Phase transitions of different binary mixtures of a bent-core (10DClPBBC) and a rod-shaped (6OO8) liquid crystal were studied using differential scanning calorimetry. For the binary mixture with 50:50 weight ratio of bent-core and rod-shaped molecules, the nematic to smectic transition occurred below the temperature of 40°C and crystallization was shifted to sub-ambient temperature. It was found that crystallization was the phase transition with the lowest apparent activation energy.