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: In this paper, the structure of various sub-phases of antiferroelectric liquid crystals, their dielectric behaviour and the electro-optical response of some of the materials studied by their group are reported.
Abstract: Antiferroelectric liquid crystals (AFLCs) are a recent class of materials in the family of liquid crystals which have high prospect of application in displays with better results as compared to conventional nematic displays. Beside technological applications, AFLCs are very interesting from the point of view of basic studies in soft condensed matter systems as these materials are showing various new sub-phases, viz. SmCα*, SmCβ*, SmCγ* and many others with distinct macroscopic properties in a narrow temperature region in addition to the most common wide-range low-temperature SmCa* phase. In the present article, we report the structure of various sub-phases of AFLCs, their dielectric behaviour and the electro-optical response of some of the materials studied by our group.
11 citations
TL;DR: Bias field, spectral, and temperature-dependent optical studies on conventional and de Vries type ferroelectric liquid crystals (FLCs) are presented in this paper. But the mixing of ethanol into FLCs strongly influences their Sm C* and Sm A* phases, due to the influence on molecular randomization.
Abstract: Bias field, spectral, and temperature-dependent optical studies on conventional and de Vries type ferroelectric liquid crystals (FLCs) are presented. The mixing of ethanol into de Vries FLCs strongly influences their Sm C* and Sm A* phases, due to the influence on molecular randomization. Such comparative optical studies may be used as an effective tool for the preliminary detection of molecular randomization in addition to other conventional techniques.
10 citations
TL;DR: In this paper, a random dielectric mode has been predicted in electroclinic liquid crystals near the transition temperature of Sm-C*-Sm-A phase, which is called random mode due to its origin from randomization of tilt.
Abstract: The dielectric properties of electroclinic and ferroelectric liquid crystal materials have been investigated in the frequency range of 100Hz–10MHz. A dielectric mode has been predicted in electroclinic liquid crystals near the transition temperature of Sm-C*–Sm-A phase. It has been observed that the investigated material has nonlayer shrinkage near the transition temperature of Sm-C*–Sm-A phase and shows anomalous behavior of dielectric spectra, tilt, and texture which is entirely different from the behavior of ferroelectric liquid crystals (FLCs). The dielectric relaxation frequency and tilt angle are almost constant with respect to temperature near the transition temperature under high bias field, which is characteristically different from FLCs. The high dielectric permittivity near Tc owing to the presence of mode contribution leads to the fact that there is an intralayer phason variation few degrees before transition. The mode has been named random mode due to its origin from randomization of tilt nea...
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TL;DR: A new family of ferroelectric smectic liquid-crystalline binary mixtures composed of achiral and chiral trifluoromethylphenylterthiophenes is presented, finding that the remnant polarization and photocurrent density in the polarized ferro electric phases increased nonlinearly with the increase in the content of the chiral component in the mixture.
Abstract: This paper presents a new family of ferroelectric smectic liquid-crystalline binary mixtures composed of achiral and chiral trifluoromethylphenylterthiophenes. The chiral symmetry breaking of the ferroelectric smectic phases can lead to chiral photovoltaic (CPV) effects, as a type of ferroelectric photovoltaic (FePV) effect, which is caused by the internal electric field originating from the spontaneous polarization. These ferroelectric properties were examined using the Sawyer-Tower method, and the CPV effect was confirmed by measuring the steady-state photocurrent response under zero bias. We found that the remnant polarization and photocurrent density in the polarized ferroelectric phases increased nonlinearly with the increase in the content of the chiral component in the mixture. Moreover, the hole mobility evaluated by time-of-flight measurements was kept constant by varying the composition. More than 40 mol % of the chiral component was required to form the polar structure, inducing the CPV effect. Binary mixture systems are advantageous for not only optimizing liquid crystal structures and temperature ranges but also facilitating the design of materials exhibiting CPV effects.
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TL;DR: In this article, a new class of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been designed and synthesized by intermolecular hydrogen bonds between mesogenic 4-decyloxybenzoic acid (10OBA) and non-mesogenic (R)-(+)-Methylsuccinic acid (MSA) which have been confirmed through experimental and theoretical studies.
Abstract: A new class of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been designed and synthesized by intermolecular hydrogen bonds between mesogenic 4-decyloxybenzoic acid (10OBA) and non-mesogenic (R)-(+)-Methylsuccinic acid (MSA) which have been confirmed through experimental and theoretical studies. Further, Mulliken population analysis clearly reveals that the existence of hydrogen bonds, strength and dynamic properties. Textural observation and its corresponding enthalpy values are analyzed by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) respectively. Paramorphic changes in Sm C* phase due to the change of refractive index, which clearly reveal that the complex could be used for filtering action in photonic devices. The transition from lone pair to π* with large stabilization energy evidently exposes the chiral phases in the present HBFLC complex. Intermolecular interaction is analyzed by using natural bond orbital (NBO) studies. The highest energy in the HOMO-LUMO shows the stable phase in the HBFLC complex. Molecular structure of the HBFLC complex possesses the monoclinic which has been evinced through x-ray analysis. The randomly oriented bunch of homogeneous molecules in Sm A* phase of the HBFLC complex is reported.
10 citations