Yu. Reznikov

Dielectric relaxation spectroscopy of a nematic liquid crystal doped with ferroelectric Sn 2 P 2 S 6 nanoparticles

It was found that doping a nematic liquid crystal (LC) with a small amount of ferroelectric nanoparticles strongly affects the dielectric properties of the system. In particular, adding the ferroelectric particles results in a shift of the absorption bands corresponding to the rotation of liquid crystal molecules around their short axes to lower frequencies and in an increase of the amplitude and with of the absorption bands. This suggests that strong interactions occur between the LC molecules and the particles, caused by the large dipole moment and high polarizability of the ferro-particles. The ferroelectric particles affect not only dielectric losses, but also dielectric permittivity of the system. Specifically, the static dielectric permittivity and the dielectric anisotropy of the suspension are more than twice that of the pure LC.

Electrically controlled surface diffraction gratings in nematic liquid crystals

Photorefractive diffraction gratings were studied in cells of homeotropically aligned pentyl-cyanobiphenyl liquid crystal. These holographic gratings were induced by the simultaneous and nonsimultaneous application of dc and coherent optical electric fields. The observed behavior was consistent with a predominantly surface-mediated photorefractive effect. Beam coupling was observed in all cases and led to a model involving screened and unscreened interfacial trapped charges driving a modulation of the easy axis. Holographic gratings could be switched on and off by the application of a small voltage.

Photoinduced Charge of Cholesteric Lc-Pitch

Abstract The effect of reversible shift of selective reflectivity band in induced cholesteric LC under the laser irradaition is observed.

Preparation of ferroelectric nanoparticles for their use in liquid crystalline colloids

In this paper we summarize our many years of experience in the preparation and optimization of stable colloids of ferroelectric nanoparticles dispersed in an isotropic carrier and in a liquid crystal host. The colloids are of interest for use in electro-optic devices, photorefractive hybrids and nonlinear optical elements. We also outline some of the most interesting features the nanoparticles bring to liquid crystals, along with the potential of these relatively new colloids.

A colloid of ferroelectric nanoparticles in a cholesteric liquid crystal

The introduction of a minor quantity of ferroelectric nanoparticles into a cholesteric mixture causes a 45% decrease of the driving voltage with both the optical cell quality and the director field in the cell remaining undisturbed. The drop of the driving voltage results from a more than twofold increase of the effective dielectric anisotropy of the nematic matrix, which is the basic component of the cholesteric compound. The results reported clearly show how promising the ferroelectric liquid crystalline (LC) nanocolloids are for various applications. In particular, they offer a unique way for an effective tuning of the dielectric, optical and electro-optic properties of LC materials in a non-synthetic way that is a new direction for the development of advanced anisotropic meso-materials. We suggest that the strong impact of ferroelectric nanoparticles on the properties of the studied chiral nematics is due to the particles permanent polarization, which produces a giant electric field around it.

Transformation of hydrogen bonding of a liquid crystal-aerosil system under the influence of an electric field☆

Abstract The transformation of hydrogen bonds in the liquid crystal (5CB)-aerosil system under the influence of an electric field is investigated with the use of IR spectroscopy methods. It is shown that aerosil addition (10 wt.%) to 5CB leads to the formation of weak hydrogen bonds between the aerosil hydroxyl groups and the π-electrons of benzene rings of 5CB (SiOH ⋯ π). Under the influence of an electric field ( U = 60 V, ƒ = 2 kHz ) these bonds undergo a rearrangement, the 5CB molecules in the aerosil pores aligning along the direction of the electric field and thereby forming a new network of hydrogen bonds.

Measurement of Azimuthal Anchoring Energy of Nematic Liquid Crystal on Photoaligning Polymer Surface

Abstract A method to determine the surface azimuthal anchoring energy of a nematic liquid crystal is proposed. The technique implies the measurement of the director deviation on the cell substrate as a function of strength and direction of the applied magnetic field. As an example, the dependence of the azimuthal anchoring coefficient on the exposure time is measured at the interface between the nematic K 15 and polyvinylcinnamate film exposed by UV light. The analogous measurements performed in a wedge cell show that the method with magnetic field is more precise.

Enhanced Dielectric Response of Liquid Crystal Ferroelectric Suspension

It was found that doping of tiny ferroelectric particles to a nematic liquid crystal(LC)strongly affects dielectric properties of the system. The doping increases dielectric response of the LC due to interaction between LC molecules and particles, which possess large dipole moment and high polarisability. The suspension reveals high dielectric response on either side of the Curie temperature, TCurie, and peculiarity at the vicinity of TCurie. This result points at retention of dipole ordering above Curie temperature that may be a result of a memory effect.

An Oblique Orientation of Nematic Liquid Crystals on a Photosensitive Aligning Polymer

Abstract The problem of an oblique orientation of a liquid crystal in cells with light induced easy orientation axis is considered. Theoretical and experimental studies of the director distribution in a cell with a photosensitive orientant, fluorinated polyvinylcinnamate polymer film, are performed. The two exposure technique for liquid crystal oblique orientation and the condition for a new anchoring transition in a cell with a photosensitive orientant are also presented.

Induced Cholesteric Liquid Crystal Polymer as a New Medium for Optical Data Storage

Induced cholesteric LCP material is suggested for optical data storage and its main parameters are measured.