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.
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.
Abstract: A 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: W415 is a chiralsmectic compound with a remarkably weak temperature dependence of its giant electroclinic effect in the liquid crystalline smectic A* phase and possesses a high spontaneous polarization in the smecto-C* phase.
Abstract: W415 is a chiral smectic compound with a remarkably weak temperature dependence of its giant electroclinic effect in the liquid crystalline smectic A* phase. Furthermore it possesses a high spontaneous polarization in the smectic C* phase. The origin of this striking electroclinic effect is the co-occurrence of a de Vries-type ordering with a weak first-order tilting transition (see the synchroton X-ray scattering profiles).
15 citations
TL;DR: In this article, a semi-fluorinated chiral liquid crystal, W504, is investigated by electro-optic, dielectric and X-ray scattering experiments, and the tilting transition in W504 is mainly an ADC model disorderorder transition, but it also has a compo...
Abstract: A new semi‐fluorinated chiral smectic liquid crystal, W504, is investigated by electro‐optic, dielectric and X‐ray scattering experiments. It exhibits a huge dielectric soft mode response, strong electroclinic effect and a birefringence which increases considerably with the director tilt angle θ; typical characteristics of a SmA*–SmC* transition following the de Vries asymmetric diffuse cone (ADC) model in which the non‐zero director tilt in SmC* arises through an ordering of tilting directions rather than an actual increase in average molecule tilt ⟨θmol⟩. In W504 a small increase in ⟨θmol⟩ of about 4° is however detected in the SmC* phase. Although the increase in molecule inclination is much less than the increase in director tilt θ, saturating close to 30°, it leads to a shrinkage of the smectic layers by about 1 A, a result of the large initial molecule tilt in the SmA* phase, ⟨θmol⟩SmA*≈30°. The tilting transition in W504 is thus mainly an ADC model disorder–order transition, but it also has a compo...
15 citations
TL;DR: In this article, a series of lactic acid derivatives was found to exhibit a rather wide antiferroelectric chiral smectic C (SmC*A) phase below the ferroelectric SmC* and paraelectric smectric A (SmA) phases.
Abstract: Rich polymorphism has been found in a new series of lactic acid derivatives. The length of a non‐chiral n‐alkyl chain plays an important role in changing the sequence and temperature range of phases. Except for one homologue with the shortest chain, all compounds exhibit a rather wide antiferroelectric chiral smectic C (SmC*A) phase below the ferroelectric (SmC*) and paraelectric smectic A (SmA) phases. The spontaneous polarisation and tilt angle were measured in the SmC* and SmC*A phases. For several compounds, small‐angle X‐ray diffraction measurements provided information about layer spacing, d. Temperature dependences, d(T), exhibit a rather large jump at the SmC*–SmC*A phase transition, but no anomaly was observed in the temperature dependences of the tilt angle and spontaneous polarisation. For one compound studied, a TGBA phase was established on the basis of the planar sample and free‐standing film observation under a polarising optical microscope. For two compounds with the longest non‐chiral cha...
15 citations
TL;DR: In this paper, the authors investigated the effect of the initial surface anchoring influence on the stability of the Smectic C phase liquid crystal in terms of its retardation switching effect and showed that in some specific initial molecular alignment case, SMC molecular behavior has in-plane only movement, resulting in almost complete suppression of out-of-plane retardation.
15 citations
TL;DR: In this article, the tendency to de Vries behavior has been described for compounds with decreasing length of non-chiral chain for homologue series exhibiting the SmA* and SmC* phases.
Abstract: Homologue series exhibiting the SmA* and SmC* phases have been studied and the tendency to de Vries behaviour has been described for compounds with decreasing length of non-chiral chain. Dielectric spectroscopy has been performed with the aim to characterize dielectric properties and compare different homologue compounds exhibiting de Vries properties with those showing classical behaviour.
13 citations
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