A. P. Fedoryako

Photoinduced Effects in Liquid Crystal Systems Containing Chiral α,β-Unsaturated Ketones

ABSTRACT Photoinduced changes have been revealed and summarized for liquid crystalline (LC) systems with helical supramolecular structures induced with chiral α,β-unsa-turated ketones. The photoinduced inversion of a helix sign was ascertained for LC mixtures containing 3R-methylcyclohexanone arylidene derivatives. This effect is accompanied with an essential enhancement of the helical twist in the photostationary state and its invariability under the following prolonged UV irradiation. For ferroelectric LC, the photoinduced inversion of a spontaneous polarization sign and a concomitant increase in its absolute value and in the smectic tilt angle are observed. The E–Z photoisomerization of chiral compounds is established to be responsible for the effects discovered.

Free oscillations in a ferroelectric liquid crystal

A description is given of experimental investigations in which free electromechanical oscillations are obtained for the first time in ferroelectric liquid crystals.

Specific Features of Electromechanical Conversion in Various Liquid Crystalline Phases

Electromechanical effect in various liquid crystalline phases—nematic, smectic A, and smectic C—is studied. It is shown that a liquid crystal (LC) sample in the nematic phase does not differ from an electromechanical converter containing an isotropic dielectric and exhibits no features characteristic of LCs at electromechanical conversion. A phenomenon similar to the piezoelectric effect may occur in ferroelectric LCs due to their biaxiality.

Ferroelectric liquid crystal mixtures containing chiral ether and ester compounds with the 2-arylidene-p-menthan-3-one skeleton

Some1R,4R-2-(4-phenylbenzylidene)-p-methane-3-one derivatives containing the ether or ester linking group between benzene rings of the arylidene fragment have been studied as chiral dopants in ferroelectric liquid crystal systems based on the eutectic mixture (1:1) of two phenylbenzoate derivatives (see paper for formula) The ferroelectric properties of these compositions (spontaneous polarization, rotation, viscosity, smectic tilt angle as well as quantitative characteristics of their concentration dependences) were compared with those for systems including chiral dopants containing no linking group. Ferroelectric parameters of the induced ferroelectric compositions studied have been shown to depend essentially on the presence of the linking group between benzene rings and its nature as well as on the number of the benzene rings in the rigid molecular core of the chiral dopants used. For all ferroelectric liquid crystal systems studied, the influence of the chiral dopants on the thermal stability of N*, SmA and SmC* mesophases has been quantified. The influence of the linking group nature in the dopant molecules on the characteristics of the systems studied is discussed taking into account results of the conformational analysis carried out by the semi-empirical AM1 and PM3 methods.

Influence of Chiral Dopant Molecular Structure on Ferroelectric Liquid Crystal Parameters

Properties of ferroelectric liquid crystal (FLC) host/chiral guest systems have been studied. The achiral smectic C systems, namely, the eutectic mixtures of phenylbenzoate derivatives and of three isomeric bis-laterally fluorinated dialkylterphenyls were used as the host materials. Dependencies of the dTi/dC on molecule structures of the components as well as concentration and temperature dependencies of main ferroelectric parameters (the spontaneous polarization, P S , the smectic tilt angle, θ, the rotational viscosity, γϕ) of the induced FLC were studied and discussed.

Parametric Interaction of Acoustic Signals in Ferroelectric Liquid Crystals

Interaction of acoustic signals was investigated in a cell of ferroelectric liquid crystal (FLC). Oscillation lines of both the initial and the combination frequencies were detected in the spectrum of the electromechanical response. Dependencies of the vibration parameters of combination frequencies on the vibrations parameters of the sound and ultrasonic excitation were investigated. Combination frequencies appear as a result of non-linear dynamical properties of FLC.

Resonance phenomena in a ferroelectric liquid crystal near the phase transition SmA-SmC*

Abstract Dynamic properties of ferroelectric liquid crystals have been studied by means of observation of electric, optical and mechanical responses to the step-like change of electric field strength. A resonance low-frequency mode interpreted as a texture one has been revealed near the phase transition SmA - SmC*. Interaction between this texture resonance mode and bending modes of glass cell plates and the synchronization effect have been found. Temperature and electric field dependences of the texture resonance mode parameters are given.

Piezoelectric effect in ferroelectric liquid crystal: A review

The data in the literature and our results of studying the piezoelectric effect in ferroelectric liquid crystals are analyzed. The existing theories of this effect in liquid crystals are discussed. The parametric transformations of electromechanical oscillations in ferroelectric liquid crystals are considered.

Resonance Mode and Pretransitional Fluctuations Near the SmA—SmC* Phase Transition

Abstract A low-frequency (0.1 – 100 kHz) resonance mode interpreted as a texture one has been investigated on ferroelectric liquid crystals (FLC). Compounds and mixtures showing different types of the phase transition into the SmC* phase (I—SmC*, N*—SmC*, SmA—SmC*) have been examined in order to find the resonance properties in the ferroelectric phase. It has been shown that the origin of the resonance response (resonance mode) is caused by strong pretransitional order parameter fluctuations in both SmA and SmC* phases near the second order SmA—SmC* phase transition. The principal factor causing the resonance mode origination is the presence of an external mechanical field in the well aligned uniform bookshelf FLC texture. An interaction between the texture resonance mode and bending modes of glass cell plates and the synchronization effect have been investigated.

Temperature dependence of oscillation parameters in ferroelectric liquid crystals

Oscillation processes have been revealed in the course of reversible polarization study in ferroelectric liquid crystals. The oscillation frequency of polarization vector has been found to be from 1 to 30 kHz. The oscillation parameters were studied as functions of temperature. Temperature dependences of the oscillation amplitude and damping decrement have been measured.