O. E. Kalinovskaya

The investigation of the relaxation processes in antiferroelectric liquid crystals by broad band dielectric and electro-optic spectroscopy

Wide band dielectric and electro-optic spectroscopy of an antiferroelectric liquid crystal (AFLC) has been carried out over a range of frequencies from 1 kHz to 1 GHz. The AFLC sample under investigation possesses a variety of different ferri-, ferro-, and antiferro-electric phases. Dielectric spectroscopy of the LC cells in the antiferroelectric phases reveals both collective and individual dynamics of molecules. In the antiferroelectric SmCA phase, three dielectric relaxation processes are found in the absence of the bias and an additional relaxation process appears under the bias field. A solution of the dynamical equation of the director subject to a weak alternating field for the anitferroelectric helix has been found. A comparison of the results of electro-optic and dielectric spectroscopy with a theoretical study enables a determination of the origin of the relaxation processes in antiferroelectric phases. The mechanism for the distortion of the antiferroelectric helix has been determined using die...

The investigation of the relaxation processes in antiferroelectric liquid crystals by electro-optic spectroscopy

Electrooptic spectroscopy of an antiferroelectric liquid crystal is carried out over a range of frequencies from 1 Hz to 100 kHz. In the antiferroelectric SmCA phase two relaxation processes are found, one at the fundamental frequency of a mode and the second at twice the frequency of a different mode. A comparison of the results of the electro-optic spectroscopy with a theoretical study of the motion of the director of an antiferroelectric helix subject to a weak alternating field enables a determination of the origin of the relaxation processes in antiferroelectric phases.

The exponential dielectric relaxation dynamics in a secondary alcohol’s supercooled liquid and glassy states

To gain insight into a recent observation that the prominent, Debye-type relaxation process observed for a primary alcohol may not be the α-relaxation process associated with molecular diffusion of a liquid [Europhys. Lett. 40, 549 (1997), J. Chem. Phys. 107, 1086 (1997)], the dielectric spectra of an uncrystallizable secondary alcohol, 5-methyl-2-hexanol, has been investigated by broadband spectroscopy. Measurements made over a temperature range from 110 to 298 K showed that three relaxation processes occur. Processes I and II have a non-Arrhenius variation of the relaxation rate with temperature, and process III an Arrhenius. Only process I, the slowest of the three, has a single relaxation rate, the other two, a broad distribution. The contribution to permittivity from process II was 0.8, i.e., ∼3% of the static permittivity, and from process III, the fastest was 0.1, i.e., ∼0.3%. It is argued that the mechanism of process I is the breaking followed by dipolar reorientation and reforming of the H-bonds...

Observation of a possible random ferroelectric liquid crystal phase

A random ferroelectric tilted smectic phase has been observed and investigated for the first time. In this phase, the molecular director in smectic layers is tilted with respect to the smectic layer normal but the tilt directions in different smectic layers are randomly oriented. This structure is confirmed by electrooptics, effective birefringence measurements and dielectric spectroscopy.

On the V-shaped switching in antiferroelectric liquid crystals

Abstract The electrooptic response of a thin cell of antiferroelectric liquid crystal is investigated as functions of frequency and temperature. It was found, that under specific conditions the FLC cell exhibits the V-shaped switching, the parameters of which are strongly dependent on the frequency of applied electric field. The frequency dependence of electrooptic response has been modelled by taking in account the phenomenon of ion transport. The conditions for a hysteresis-free V-shaped switching were found from the model.

Nonexponential dielectric relaxation dynamics in supercooled liquid and glassy states of isoamyl bromide and 2-methylpentane mixtures

The dielectric spectra of mixtures of the polar solute isoamyl bromide in 2-methylpentane have been investigated in the frequency range 1 mHz to 1 MHz and in the temperature range approaching the glass transition temperature. The results obtained from the spectra are compared with those obtained recently [J. Chem. Phys. 111, 10979 (1999)] on pure isoamyl bromide. It is found that on increasing dilution with the nonpolar solvent, the width of the curves of the dielectric spectra increase significantly, and this is reflected in the increase in the nonexponential nature of the relaxation dynamics. This is found to be a consequence of the decrease in the cooperativity of the relaxation dynamics and or an increase in the heterogeneity of the solution. The data are found to fit the Havriliak–Negami equation extremely well. The data at low and high frequencies also fits the “universal law,” since the latter is a low and high frequencies limiting case of the Havriliak–Negami equation. The scaling parameters of th...

The relaxation processes in helical antiferroelectric liquid crystals

Abstract The collective relaxation processes in antiferroelectric liquid crystals are investigated both theoretically and experimentally. A comparison of results for the electro-optic and dielectric spectroscopy with a solution for the dynamical equation enables a determination of the origin of the relaxation processes in antiferroelectric phases.

Observation of exotic subphases in an antiferroelectric liquid crystal

Abstract Dielectric and polarization measurements are carried out for characterizing the subphases in a antiferroelectric liquid crystal with a variety of ferri-, ferro- and antiferroelectric phases. It is found that ferri-phases in between SmCA are somewhat unstable and disordered; the reasons of the instability are given in terms of the ANNI model. A meta-stable field induced ferri phase has been found thus confirming our discovery (Panarin et al Phys. Rev. E 55, 4345, 1997) of such a ferri phase. A surface domain mode having a frequency about a decade higher than that of the Goldstone mode has also been observed for the first time in a antiferroelectric liquid crystal.

Investigation of the Ferrielectric Subphase with qT > 1/2 under Bias Voltage

Abstract The properties of Ferrielectric phase with qT >1/2 have been investigated using broadband dielectric spectroscopy and polarization measurements under the bias voltage. The field -induced sequence of phase transitions is found to be different from those of the conventional ferrielectric phases with qT≤1/2.

A comparison of orientational behaviour and rotational bias in SmC*, SmCa* and SmCγ* phases of an antiferroelectric liquid crystal studied by FT-IR spectroscopy

Abstract Polarised infrared Spectroscopy is used to study the behaviour of SmC*, SmCA* and SmCγ* phases of an antiferroelectric liquid crystal material. The degree of molecular orientation is expressed in terms of the dichroic ratio obtained from the absorbance profiles for various applied voltages. The molecular tilt angle is found as the absorbance profiles of the various peaks rotate clockwise and anticlockwise with the sign of the applied field. The absorbance profiles of the stretching bands are quantitatively analysed and the biasing parameters of the transition dipole moments located in the molecular core for each phase are calculated and compared.