H. Sverenyák

The effect of a lateral substituent on the mesomorphic properties in a series of ferroelectric liquid crystals with a 2-alkoxypropionate unit

A new series of ferroelectric liquid crystal materials containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit has been synthesized and investigated. These materials exhibit a wide temperature range of ferroelectric SmC* phase on cooling (including supercooling) with a very high spontaneous polarization. All phase transition temperatures are lower when compared with those of similar non-substituted materials. In comparison with the compounds containing the lateral methoxy group, only the SmC*-Cr transition changed significantly. The values of spontaneous polarization are mostly increased compared with both non-substituted and methoxy substituted compounds.

New series of ferroelectric liquid crystals with four ester groups

Three series of ferroelectric liquid crystals have been synthesized, having three ester groups in the mesogenic core and one ester group in the chiral chain. The ester groups introduced into the core decrease the temperature of crystallization, which results in a broad temperature range ferroelectric smectic C phase in homologues with a long non-chiral chain. These phases exhibit a high spontaneous polarization and relatively short pitch of the helical structure.

Thickness dependent low frequency relaxations in ferroelectric liquid crystals with different temperature dependence of the helix pitch

A low frequency relaxation mode 1 has been detected in ferroelectric phases of three materials. The relaxation frequency and the dielectric strength of this mode depend strongly on the sample thickness, but their temperature dependences are qualitatively different in the materials studied, reflecting the behaviour of the helicoidal structure of these materials. This mode has been attributed to a superposition of the Goldstone and thickness modes when the helicoidal structure exists and to the thickness mode only, when the helix is unwound. In addition, with one material, mode 2 has been detected at still lower frequencies, and this also exhibits a strong sample thickness dependence. It was attributed to fluctuations of the director field modified by a non-homogeneous ionic charge distribution across the sample. As both modes 1 and 2 are strongly sample thickness dependent, they do not represent bulk properties of the materials studied, but reflect the structure in real samples, which is determined by surf...

Synthesis and mesomorphic properties of a new ferroelectric liquid crystal with 2-alkoxypropionate chiral groups

Abstract Two series of new chiral substances with 2-alkoxypropionate chiral groups have been synthetized. All compounds exhibit very wide ferroelectric SmC* phases with a high spontaneous polarization.

Helix twist inversion in ferroelectric liquid crystals with one chiral centre

Abstract The helix twist inversion in the chiral smectic C phase was studied for two new homologous series of lactic acid derivatives. The inversion phenomenon was attributed to a competition between spatial conformers leading to opposite helix handedness. The temperature of inversion was found to increase with increasing length of the chiral molecular tail. With all substances studied, high values of the spontaneous polarization P s were found which did not reach saturation on cooling, in spite of a saturated tilt angle θs.

The effect of a lateral methoxy group on the mesomorphic properties of ferroelectric liquid crystals

Abstract A new series of ferroelectric liquid crystal materials having the methoxy group substituted in an aromatic ring of the mesogenic core has been synthetized and characterized. This electron-donor methoxy group makes the ferroelectric S∗c phase narrower in range and monotropic when compared to the series with the unsubstituted molecules, the values of the spontaneous polarization remaining unaffected.

Dielectric and electrooptical study of a new antiferroelectric liquid crystal with the thiobenzoate group

Abstract A new thiobenzoate compound exhibits polar phases SmCα*, ferroelectric SmC*, ferrielectric SmC* and antiferroelectric SmC*γ. From the electrooptic intensity and the permittivity measured in the frequency range 10 ÷ 106 Hz the soft mode relaxation frequency in the paraelectric SmA phase and the Goldstone mode relaxation frequency in the polar phases have been determined. In the polar phases the temperature dependences of both the spontaneous polarizarion and the tilt angle are measured under an electric field high enough to bring about the saturated ferroelectric state. The dependencies are smooth within the entire temperature range studied indicating all the studied phases are indistinguishable under high electric field.

The Thickness Mode Contribution to the Permittivity of Ferroelectric Liquid Crystals

Abstract Dielectric properties of a material prepared of valine in the ferroelectric SmC* phase are studied in the frequency range 100 Hz ÷ 1 MHz and for the sample thickness d between 6 and 100 pm for both helicoidal and twisted sample structure. In all studied samples a low frequency relaxation has been found with the relaxation frequency proportional to 1/d2 and with the contribution to permittivity proportional to d2 . We suggest this relaxation to be assigned to a ‘thickness mode‘, which is a fluctuation of the molecular twist existing within the smectic layers in the direction of the sample plane normal. This twist deformation existing in both helicoidal and twisted samples is fixed by the anchoring on the sample surfaces. It is shown that the thickness mode is an important source of permittivity in the SmC* phase of the studied material.

The new SmC* phase with periodic in-layer director modulation

Abstract Different types of 1 D and 2D periodic systems of defects were detected in free suspended films of chiral SmC and SmCA materials with the helical structure spontaneously unwound. Observed textures were attributed to the appearence of the phase with the periodic long range director modulations within the smectics layers.

SYNTHESIS AND MESOMORPHIC PROPERTIES OF (S)-LACTIC ACID DERIVATIVES CONTAINING SEVERAL ESTER LINKAGES IN THE CORE

Abstract Synthesis and mesogenic properties of new substances 1 with several ester linkages in the core are reported. All compounds show chiral smectic C phase in broad temperature range except the lower members of series. One more carboxy group conjugated to the semi rigid core leads to appearing the SmA phase instead of the cholesteric phase and decreases the spontaneous polarisation in the SmC* phase.