L. Bata

Electromechanical effect in S*c liquid crystals

Detailed analysis is given of the electromechanical effect in planar S*c liquid crystals. Experimental data are presented for the amplitude of the vibration as a function of the frequency, applied voltage and temperature. The existence and the frequency dependence of the linear electromechanical effect is explained within the framework of a continuum theory.

A chiral side-chain polymer with layered structure

Abstract A chiral side-chain polymer was synthesized and its chemical structure was proved by infrared spectroscopy. According to the X-ray diffraction studies the polymer exhibited smectic type ordering however it did not show any birefringence macroscopically.

Non-linear electromechanical response of S∗C liquid crystals

Abstract The non-linear part of the electromechanical response of four S∗C liquid crystals were investigated. The second harmonic frequency vibrational spectra, the electric field, and the temperature dependences are presented. The experimental results are interpreted in terms of a microscopic process.

Molecular Relaxation in hi Ghly Ordered Orthogonal Smectic SA, SB and SE Phases

Abstract Dielectric relaxation and calorimetric investigations were perforemed on different smectic phases. Discountinuities of the critical frequency were found at both SA-SB and SB-SE phase transitions. SA and SE structures can be regarded as two-dimensional liquid and two-dimensional crystal, respectively. The low frequency dielectric dispersion presented here demonstrates the difference btween the SE and a three-dimensional cyrstal where this phenomena is absent.

Structure of polymer networks dispersed in liquid crystals: Small angle neutron scattering study

Abstract We present the first small angle neutron scattering studies on liquid crystal polymer composite systems, where small amounts of polymers are dispersed in liquid crystals. A recent study (A. Jakli, D. R. Kim, L. C. Chien and A. Saupe, 1992, Appl. Phys. 72, 3161) showed that even 1 wt% of polymer can induce phase separation in the form of fibres. We have found that the cross-sectional radius of such fibres is typically 300 A and they have rough surfaces. The spatial distribution of the fibres does not change during the phase transitions of the liquid crystal. We have found that there is a correlation between the size of the separated polymer particles and the roughness of their surfaces: larger objects have less smooth surfaces.

Chiral smectic side-chain copolymers—I. Synthesis and phase behaviour

Abstract Copolymers have been synthesized in which chiral monomer units are combined with those of a tilted smectic homopolymer. Copolymers with the proportion of chiral units not exceeding 37% form a S F ∗ phase and have therefore ferroelectric properties.

Continuum Theory of Uniformly Layered Chiral Smectic C* in an Electromagnetic Field

Abstract A linearized continuum theory combining electro-, hydro- and thermodynamics of smectic C liquid crystals is presented. Electromagnetic field is incorporated into the balance equations and generalized free energy is introduced. Reversible and irreversible proesses are handled separately. Constitutive equations are derived for both chiral and achiral smectic C phases. The connection between chirality and the existence of cross-effects is discussed. A physical interpretation of the final equations is also given. It is shown that in the chiral smectic C* phase a new effect, viz. electromechanical coupling, may exist.

Properties of a Homologous Series of Ferroelectric Liquid Crystals

Abstract A homologous series of MBOPEnOBA chiral compounds has heen synthesized and some chemical and physical properties of the components as well as that of a binary mixture has heen studied. Measurements of the spontaneous polarization and the pitch are presented and results of eutectic, dielectric, electrooptic and electromechanical investigations are given.

Structural properties of the ferroelectric liquid crystal mixtures based on the homologous series of alkoxyphenyl alkoxy benzoates

Abstract The temperature dependence of the layer spacings and the average intermolecular distances were studied in smectic A, C, B and nematic phases by X-ray diffraction on non-oriented samples. Two representatives of 4-n-alkoxyphenyl 4′-n-alkoxy benzoates, furthermore their eutectic binary mixture, and ternary ferroelectric mixtures obtained by the chiral additive of (R)-(1-methylheptyl)-1, 1′-4′-1′-terphyenyl-1, 4′-dicarboxilate used in different concentrations were investigated by small and large angle measurements as well.

Electromechanical effect in surface stabilized and unwound SC* liquid crystals

Abstract Applying an A.C. electric field to a planar oriented SC* liquid crystal sample, a shear flow occurs parallel to the bounding plates and perpendicular to the helical axis. We have investigated this so-called electromechanical effect by applying different D.C. bias electric fields superposed on a constant A.C. field. The amplitude of the mechanical vibration was measured versus the bias field in different samples. From the results, structural models of the surface stabilized and unwound samples were tested.