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Journal ArticleDOI

Optical and x-ray evidence of the "de Vries" Sm-A*-Sm-C* transition in a non-layer-shrinkage ferroelectric liquid crystal with very weak interlayer tilt correlation.

11 Sep 2002-Physical Review E (American Physical Society)-Vol. 66, Iss: 3, pp 031703-031703

TL;DR: A non-layer-shrinkage fluorinated ferroelectric liquid crystal compound, 8422[2F3], has been characterized by means of optical, x-ray, and calorimetric methods and there is strong evidence that the second-order Sm-A*-Sm-C* transition is well described by the diffuse cone model of de Vries.

AbstractA non-layer-shrinkage fluorinated ferroelectric liquid crystal compound, 8422[2F3], has been characterized by means of optical, x-ray, and calorimetric methods. The orientational distribution within macroscopic volumes, determined through wide-angle x-ray scattering and birefringence measurements, was found to be identical in the $\mathrm{Sm}\ensuremath{-}{A}^{*}$ and helical $\mathrm{Sm}\ensuremath{-}{C}^{*}$ phases. Together with the absence of layer shrinkage, this constitutes strong evidence that the second-order $\mathrm{Sm}\ensuremath{-}{A}^{*}--\mathrm{Sm}\ensuremath{-}{C}^{*}$ transition in this material is well described by the diffuse cone model of de Vries. The absolute values of the layer spacing show that the molecules aggregate to antiparallel pairs. The molecular interaction across the layer boundaries will then occur only between fluorine atoms, leading to unusually weak interlayer tilt direction correlation. This explains the experimental observations of a very easily disturbed $\mathrm{Sm}\ensuremath{-}{C}^{*}$ helix and a peculiar surface-stabilized texture. Tilt angle and birefringence values as a function of field and temperature have been evaluated in the $\mathrm{Sm}\ensuremath{-}{A}^{*}$ and $\mathrm{Sm}\ensuremath{-}{C}^{*}$ phases and the results corroborate the conclusions from the x-ray investigations.

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TL;DR: The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionIC liquid crystals and particularly to ionic liquids will also be provided.
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437 citations


Journal ArticleDOI
TL;DR: This Review discusses some of the topics of highest interest in current smectic liquid crystal research, and address application-relevant research (de Vries-type tilting transitions without defect generation and high-tilt antiferroelectric liquid crystals with perfect dark state) as well as more curiosity-driven research.
Abstract: Interest in the smectic liquid-crystalline state of matter received a substantial boost with the discovery by Meyer in the mid-1970s that a chiral smectic C (SmC*) phase exhibits a spontaneous electric polarization, and with the subsequent demonstration by Clark and Lagerwall of the surface-stabilized SmC* ferroelectric liquid crystal at the beginning of the 1980s. Since then, chiral smectic phases and their plethora of polar effects have dominated the research in this field, which today has reached a mature state where the first commercial microdisplay applications are now shipping in millions-per-year quantities. In this Review we discuss some of the topics of highest interest in current smectic liquid crystal research, and address application-relevant research (de Vries-type tilting transitions without defect generation and high-tilt antiferroelectric liquid crystals with perfect dark state) as well as more curiosity-driven research (the nature and origin of the chiral smectic C subphases and their intermediate frustrated states between ferro- and antiferroelectricity).

263 citations


Journal ArticleDOI
Abstract: Bent-core mesogens derived from 4-cyanoresorcinol with terminal alkyl chains have been synthesized and investigated by polarizing microscopy, XRD and electro-optical methods. Short chain compounds have exclusively nematic phases which can be cooled to ambient temperature. These nematic phases are similar to ordinary nematic phases with only nearest neighbour correlation (N) whereas long chain compounds form SmC-type cybotactic clusters and these cybotactic nematic phases (NcybC) can be regarded as strongly fragmented SmC phases. The chain length dependent as well as temperature dependent structural transition from N to NcybC is continuous and associated with a change of the position and intensity of the small angle scattering in the XRD patterns. Moreover, a temperature dependent stepwise transition from cybotactic nematic phases to different types of non-polar and tilted smectic phases (SmC(I) and SmC(II)) is observed with a mesophase composed of elongated, but not yet fused cybotactic clusters (CybC) as an intermediate state of this transition. This improves the understanding of the nature and special properties of the nematic phases formed by bent-core molecules as well as their transition to smectic phases and it paves the way to new materials with spontaneous or field-induced biaxial nematic phases at ambient temperatures.

198 citations


Journal ArticleDOI
TL;DR: Measurements of smectic layer spacing d as a function of temperature by small-angle X-ray scattering (SAXS) combined with optical tilt angle measurements revealed that compounds 3(n) are characterized by low orientational and high translational order, which is consistent with theoretical predictions that such materials should exhibit de Vries-like properties.
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74 citations


Journal ArticleDOI
TL;DR: This critical review focuses on the induction of polar order in smectic liquid crystal phases by dopants with axially chiral cores, and should be of interest to all practitioners of supramolecular chemistry.
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64 citations