arXiv subjects

Tibor Tóth-Katona

Publications and source records attributed to Tibor Tóth-Katona.

6 recordsLinked to original sources

arXiv2020

Photoalignment at the nematic liquid crystal - polymer interface: the importance of the liquid crystalline molecular structure

The influence of the molecular structure of the nematic liquid crystal (NLC) on the photoalignment process at the NLC -- polymer interface has been investigated experimentally. NLCs having exclusively phenyl-, or cyclohexane rings in the rigid core, as well as NLCs containing both phenyl and cyclohexane groups have been considered. Substantial differences have been found in the photoalignment process depending on the molecular structure of the NLC, supporting the assumption that the polymer -- NLC interface should be regarded as a coupled system, where the two components mutually influence each other. A phenomenological explanation is given for the observed differences.

cond-mat.soft↗

arXiv2019

Photoalignment at the nematic liquid crystal - polymer interface: experimental evidence of three-dimensional reorientation

We provide experimental evidence that photoalignment at the nematic liquid crystal (NLC) - polymer interface can not be simply considered as a two-dimensional process. Moreover, our experiments clearly indicate that the photoaligning process does not depend on the individual properties of the NLC material and those of the interfacing polymer exclusively. According to our measurements, the polymer and the NLC layer "sense-each-other", i.e., the polymer-liquid crystal interface should be regarded as a coupled system, where the two components mutually influence each other. Furthermore, we show that the temperature induced anchoring transition also has to be taken into account for the complete description of the photoalignment mechanism.

cond-mat.soft↗

arXiv2016

Investigation of supramolecular architectures of bent-shaped pyridine derivatives: from a three-ring crystalline compound towards five-ring mesogens

In searching for novel photoactive liquid crystals, we have synthesized a series of five-ring pyridine-based bent-core compounds bearing different substituents at the peripheral phenyl rings (CH3O, Cl and NO2). Their mesomorphic behaviour has been investigated by polarizing optical microscopy, differential scanning calorimetry and X-ray scattering, and then compared with the unsubstituted parent compound. The introduction of the methoxy groups at the peripheral phenyl rings of the bent core results in a non-mesomorphic compound, whereas the chloro- and nitro-substituted compounds form enantiotropic B1-like phases. Significant changes of the textures and transition temperatures of the mesophase have been observed under UV light. The presented investigation of the mesomorphic properties of the synthesized compounds, coupled with analysis of the molecular packing of the related three-ring compounds, will help to design self-organized molecules suitable for UV indicators.

physics.chem-ph↗

arXiv2014

Low magnetic field induced capacitance changes in ferronematics

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 Fe$_3$O$_4$ nanoparticles in a nematic liquid crystal has been studied experimentally. The volume concentration of nanoparticles was $ϕ_1$ = 10$^{-4}$ and $ϕ_2$ = 10$^{-3}$. 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.

cond-mat.soft↗

arXiv2014

Laser-induced instabilities in liquid crystal cells with a photosensitive substrate

Liquid crystal layers sandwiched between a reference plate and a photosensitive substrate were investigated. We focused on the reverse geometry, where the cell was illuminated by a laser beam from the reference side. In planar cells instabilities occurred, static and dynamic ones, depending on the angle between the laser polarization and the director orientation on the reference plate. In cells where the molecules were aligned along the normal of the reference plate, dynamic pattern was observed at all angles of polarization. A simple model based on a photo-induced surface torque gives account of the findings. Light scattering studies revealed some basic properties of the instabilities.

cond-mat.soft↗

arXiv2003

Distribution of injected power fluctuations in electroconvection

We report on the distribution spectra of the fluctations in the amount of power injected into a liquid crystal undergoing electroconvective flow. The probability distribution functions (PDFs) of the fluctuations as well as the magnitude of the fluctuations have been determined in a wide range of imposed stress both for `unconfined' and `confined' flow geometries. These spectra are compared to those found in other systems held far from equilibrium, and find that in certain conditions we obtain the ''universal'' PDF form reported in [Phys. Rev. Lett. {\bf 84}, 3744 (2000)]. Moreover, the PDF approaches this universal form via an interesting mechanism whereby the distribution's negative tail evolves towards form in a different manner than the positive tail.

nlin.PS↗