Vladimíra Novotná

Novel liquid crystals based on [1]benzothieno[3,2- b][1]benzothiophene

Four series of new [1]benzothieno[3,2- b][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmCA* phase just below the SmA phase. The SmA-SmCA* phase transition has been studied using DSC and dielectric spectroscopy. In the SmCA* phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain.

A novel type of banana liquid crystals based on 1-substituted naphthalene-2,7-diol cores

The effect of lateral 1-substitution in naphthalene-2,7-diol with CH3, CN and Cl on mesomorphic properties is studied. DSC and X-ray diffraction, texture observation and dielectric measurements have been performed. For the non-substituted core the high-temperature BX phase and the B4 phase occur while in CH3 and Cl substituted compounds the B2 phases are found. In the CN derivatives, besides the crystalline-like phase N, the phase transition between the chiral B2 and racemic B2 phases is observed.

New ferroelectric and antiferroelectric liquid crystalline materials containing differing numbers of lactate units

A new series of chiral liquid crystalline materials having the same rigid core containing a keto group, and various numbers of (S)-lactate groups in the chiral segment, has been synthesized and studied. All the compounds contain a branched terminal alkyl chain derived from (S)-2-methylbutanol. The influence of the number of lactate units on mesogenic behaviour has been studied. All the compounds show the paraelectric SmA phase and the ferroelectric SmC* phase over rather wide temperature ranges. The antiferroelectric SmCA* phase was observed for the compound possessing two lactate groups.

Novel hockey‐stick mesogens with the nematic, synclinic and anticlinic smectic C phase sequence

New hockey‐stick mesogens have been synthesised and their mesomorphic properties studied. The molecular structure consists of a laterally substituted central naphthalene unit prolonged by two non‐symmetrical arms, both of which contain ester units of identical orientation. The shorter arm possesses only one and the longer arm three benzene rings. Nematic, synclinic smectic C and anticlinic smectic C phases were identified and their physical properties studied. No banana‐type ordering producing dipolar phases has been found.

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...

Novel polymerizable bent‐shaped monomeric molecules

Novel bent‐shaped mesogens based on substituted naphthalene‐2,7‐diol, possessing a double bond at the end of terminal branches, have been synthesized and characterized. A variety of banana‐mesophases has been found, depending on the type of lateral substitution. Increasing the length of the alkyl chain leads to the appearance of the SmCAPA phase for two of the compounds synthesized. Under an electric field a transition into the SmCSPF phase takes place and a tilt angle close to 45° has been found. These materials are appropriate for the preparation of polymeric materials.

Laterally substituted naphthalene‐2,7‐diol‐based bent‐shaped liquid crystals

Novel series of laterally 1‐substitued (H, Cl, CH3, CN, NO2) naphthalene‐2,7‐diol based liquid crystals were synthesized and their mesomorphic properties identified using DSC studies, texture observation, X‐ray investigations and electro‐optical measurements. Depending on the chain length and type of lateral substitution, the compounds exhibit a variety of mesophases. In materials with short alkyl chains, the rectangular columnar B1 phase was found. Increasing the alkyl chain length for the non‐substituted core causes the appearance of the so‐called BN phase. In CH3‐ and Cl‐substituted compounds, the antiferroelectric B2 phase (SmCAPA) was found. Introduction of the CN and NO2 substituents led to the formation of the B7 phase.

A nematic-polar columnar phase sequence in new bent-shaped liquid crystals based on a 7-hydroxynaphthalene-2-carboxylic acid core

Mesomorphic properties of new bent-shaped liquid crystals based on 7-hydroxynaphthalene-2-carboxylic acid are presented. The central unit of the molecular core was also modified by substitution of the chlorine atom or methyl group. Texture and calorimetric studies, as well as electrooptical, X-ray and dielectric measurements of selected compounds were performed. For long homologues the lamellar B2 phase was observed, while for shorter homologues two-dimensional columnar phases were found, built of layer fragments with the electron density modulation plane perpendicular to polarization direction. Based on X-ray patterns, two types of modulated polar columnar phases were distinguished, having oblique or orthogonal centred crystallographic unit cells and differing in relative position of the neighbouring layer fragments. For some homologues above these phases the nematic phase was also formed.

New chlorine‐substituted liquid crystals possessing frustrated TGBA and SmQ phases

Several series of chlorine‐substituted rod‐like liquid crystalline compounds have been synthesised containing a different number of lactate units in the chiral chain. Sequences of phases and phase transition temperatures were determined by differential scanning calorimetry, polarising optical microscopy and X‐ray diffraction studies. Depending on the molecule structure, the materials possess a rich variety of mesophases, i.e. the paraelectric chiral smectic A (SmA*), ferroelectric chiral smectic C (SmC*) and antiferroelectric smectic C (SmCA*) phases. Additionally, some compounds with one and two lactate groups exhibit the frustrated antiferroelectric twist grain boundary (TGBA) and smectic Q (SmQ) phases, respectively. The existence of the SmQ phase ordered in two directions was confirmed by X‐ray diffraction on a non‐oriented sample. The effects of the non‐chiral chain length and number of the chiral lactate groups on the mesomorphic properties, spontaneous polarisation, spontaneous tilt angle and complex permittivity have been studied and discussed.

New antiferroelectric liquid crystalline materials containing a keto group and two lactate groups

New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases.