K. Czupryński

Influence of alkoxy chain length and fluorosubstitution on mesogenic and spectral properties of high tilted antiferroelectric esters

The synthesis and properties of a few dozen highly evolved analogues of (S)-MHPOBC are reported. The liquid crystal phases, and phase transition temperatures and enthalpies, as evidenced by polarized optical microscopy and differential scanning calorimetry, respectively, are given. The helical pitch in pure compounds and some mixtures is estimated using the selective reflection method. All of the compounds show antiferroelectric phases, and some key structure–property relationships for the new materials are reported. Specifically, it is found that the length of the oligomethylene segment of a novel partially fluorinated alkoxy ether tail incorporated into the structures strongly influences the stability of the antiferroelectric phase and the observed phase sequences, as well as the values of the helical pitch and its temperature dependence. The formulation of a family of broad temperature range eutectic mixtures possessing the highly desirable orthoconic antiferroelectric phases with long helical pitch is described.

X-ray diffraction, optical birefringence, dielectric and phase transition properties of the long homologous series of nematogens 4-(trans -4′- n -alkylcyclohexyl) isothiocyanatobenzenes

The temperature dependence of density, refractive indices, apparent molecular length and intermolecular distance of 11CHBT, are reported, together with the static dielectric permittivities, ε∥, ε┴, ε iso of 11CHBT and 12CHBT; the effect of chain length on various physical properties of the CHBT series is also discussed. All the temperatures T m, T NI and T NCr show an odd-even (OE) effect, but transition enthalpies ΔH m and ΔH c show no such behaviour. T m, T NI and T NCr and ΔH m are found to increase with chain length, while ΔH c shows a maxima at n = 6. At the common reduced temperature T* = 0.98 TNI, the density of the compounds are found to decrease with increasing chain length while the polarizability parameters αe, αo and α increase. However, the volume expansion coefficient, polarizability anisotropy and normalized polarizability anisotropy show a distinct OE effect. Similarly, n e decreases smoothly with chain length but n o and Δn show an OE effect like ε┴ and Δε. The ratio ln ⟨P 2⟩ /ln ⟨ P 4⟩ remains closer to Faber theory than MS theory. Effective dipole moments are found to be approximately constant in the series; antiparallel association is observed in all the members. Kirkwood correlation factors g┴ and Δg are found to exhibit an OE effect like ε∥ and ε∥, but g∥ and ε∥ show no such effect. The effects of substitution in the core and end polar group on these properties are also discussed.

New antiferroelectric compounds containing partially fluorinated terminal chains. Synthesis and mesomorphic properties

Abstract Methods for preparing optically active hydroxyesters: 1-hydroxy-4-(1-methylheptyloxycarbonyl)benzene and 4-hydroxy-4′-(1-methylheptyloxy-carbonyl)biphenyl, 4-(1-methylheptyloxycarbonyl)phenyl 4′-hydroxybiphenyl-4-carboxylate and 4′-(1-methylheptyloxy carbonyl)biphenyl-4-yl 4-hydroxybenzoate have been elaborated. These compounds were used as intermediates for preparing liquid crystalline homologous series of di- and triesters exhibiting tilted smectic phases CA* and C*. The phase transitions have been measured by DSC and thermomicroscopic methods and the smectic phases have been identified by microscopic textures and miscibility studies.

Synthesis and Mesomorphic Properties of Chiral Esters Comprising Partially Fluorinated Alkoxyalkoxy Terminal Chains and a 1-methylheptyl Chiral Moiety

Two structurally similar homologous series of chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their synthetic routes and mesomorphic properties, such as phase transitions temperatures and enthalpies, are characterized by polarizing optical microscope and differential scanning calorimetry.

Nematic Phases Created in Binary Mixtures of Smectics A

Abstract It is shown that the forming of nematic mixtures composed uniquely of compounds with the smectic phase A is possible. The nematic phase is created as a result of the weakening of intermolecular attraction forces in the disturbed smectic layers. Many examples are given of binary mixtures in which induction of the nematic phase is observed or an enhancement of the nematic phase at the cost of the smectic phase takes place. The effect of the molecular structure and of the properties of the smecticphase A on its destabilization in a mixture and the creation of the nematic gap between the smectic A regions are discussed. The most characteristic features of the phase diagrams related to the S→I and S→N phase transitions and the accompanying changes of enthalpy of these phase transitions, of density and viscosity are shown in detail by way of example of binary mixtures composed of 5-n-alkyl-2-(4′-isothiocyanatophenyl)-1,3-dioxanes (smectic A1) and 80CB, or 120CB or 12CB (smectic Ad).

An assessment of carborane-containing liquid crystals for potential device application

Two 4-alkoxyphenyl 12-pentylcarborane-1-carboxylate nematic liquid crystals have been synthesized. The materials are found to exhibit ideal mixing of nematic phases in their binary mixtures with analogous bicyclo[2.2.2]octane derivatives and with the polar nematogen 4-(4-isothiocyanatophenyl)-1-(trans-hexyl)cyclohexane. The smectic phases for the bicyclo[2.2.2]octanes are destabilized by addition of the carborane derivative. For carborane compound 5BC5 the extrapolated dielectric anisotropy and measured optical anisotropy are 1.3 and 0.057 respectively at 20°C. The refractive indices have been correlated with the calculated electronic polarizabilities and the low birefringence measured for 5BC5 can, at least in part, be attributed to the carborane cylindrical symmetry.

Synthesis and Mesomorphic Characteristic of Bicyclo-(2,2,2)Octane Derivatives with the -NCS Terminal Group

Abstract Compounds containing in their molecule an alkyl substituted bicyclo(2,2,2)octane ring and the phenylisothiocyanato group bonded to it directly or via bridging group such as -COO-, -OCO-, -CH2-CH2- or -CH2O- have been synthesized. The phase transition temperatures, melting enthalpies and viscosities of these compounds have been determined and their suitability as components of nematic mixtures has been tested.

Determination of molecular parameters of the MHPB(H)PBC and MHPB(F)PBC antiferroelectric liquid crystals

Abstract Two investigated antiferroelectric liquid crystals, MHPB(H)PBC and MHPB(F)PBC, were synthesized [1] and some their physical properties were described earlier [2]. Apart of the above, MHPB(H)PBC and MHPB(F)PBC have been studied by means of dielectric, densitometric, refractometric and X-ray measurements. Spontaneous polarization P s and tilt angle θ in ferro- (SmC*) and antiferroelectric (SmCA*) phases of MHPB(H)PBC and MHPB(F)PBC have also been investigated. Transverse α1 and longitudinal α1 molecular polarizabilities have been calculated from the ordinary n 0 and extraordinary n e refractive indices and density ρ of MHPB(H)PBC and MHPB(F)PBC, using Neugebauers, Vuks and Lorentz equations with both Haller and Subramhanyama extrapolation procedures. Effective values of the molecular dipole moment μ have been calculated from electric permittivity ε in the 1 phases of these compounds, using Maier and Meier equation.

New liquid-crystalline isothiocyanates with high clearing points, low viscosities and strong nematic character

Abstract Bi-, tri- and tetra-ring liquid-crystalline compounds with an isothiocyanate group in the terminal position of the molecule and with an ethylene group in the central position have been synthesized. Phenyl, cyclohexyl, bicyclo[2,2,2]octyl, 1,3-dioxane and pyrimidinyl were used as the ring systems. Their transition temperatures and melting enthalpies have been determined. The relationship between the order of the rings in the molecule and the clearing points and melting points of the compounds is discussed. It is shown that these compounds are valuable components of liquid crystal mixtures, since they effectively raise their clearing points yet only have a small effect on the viscosity.

Bicomponent Systems with Induced or Enhanced Antirerroelectric SmCA* Phase

Abstract A new method of the formulation of liquid crystalline antiferroelectric (CA*) materials from smectic C* and smectic A components is demonstrated. The phase diagrams of the induced CA* systems and the temperature dependence of their smectic layer spacings and switching behavior are shown.