EFFECT OF DYNAMIC CONFORMATION DISTRIBUTIONS ON MOLECULAR TILT IN CHIRAL SMECTIC LIQUID CRYSTALS

1991 ◽  
Vol 05 (12) ◽  
pp. 821-826
Author(s):  
SIN-DOO LEE ◽  
J. S. PATEL ◽  
J. W. GOODBY
Keyword(s):  
Liquid Crystals ◽  
Energy Barrier ◽  
Liquid Crystalline ◽  
Characteristic Temperature ◽  
Anomalous Behavior ◽  
Rotational Barrier ◽  
Smectic Liquid Crystals ◽  
Smectic A ◽  
Sign Inversion

It is shown that for some chiral smectic A materials the field-induced molecular tilt undergoes a peculiar sign inversion with respect to the layer normal as the temperature increases. The induced molecular tilt vanishes at a characteristic temperature in the smectic A state. This anomalous behavior can be described in terms of a dynamically fluctuating mixture of at least two molecular conformers, separated by an energy barrier in their liquid-crystalline states. The energy barrier between these two conformers is found to be comparable to the rotational barrier in normal hydrocarbons.

Experimental and computational (DFT) studies on induced orthogonal smectic A∗ phase in hydrogen-bonded ferroelectric liquid crystals

2018 ◽  
Vol 32 (21) ◽  
pp. 1850223 ◽  
Author(s):  
P. Subhasri ◽  
R. Jayaprakasam ◽  
V. N. Vijayakumar
Keyword(s):  
Liquid Crystals ◽  
Molecular Orbital ◽  
Density Functional ◽  
Liquid Crystalline ◽  
Proton Acceptor ◽  
Dft Studies ◽  
Ferroelectric Liquid Crystals ◽  
Smectic A ◽  
Present Complex ◽  
Hydrogen Bonded

Hydrogen-bonded ferroelectric liquid crystals (HBFLC) are designed and synthesized from nonmesogenic chiral proton donor compound of (R)-([Formula: see text])-Methylsuccinic acid (MSA) and mesogenic proton acceptor compound of 4-undecyloxybenzoic acid (11OBA) in a different mole ratio. Intermolecular hydrogen bonds (H-bond) between the nonmesogenic and mesogenic compounds have been confirmed through experimental Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) computational studies. The steric hindrance and inductive effects of the present complex and its influence on the structure are discussed. A rich phase polymorphism in the liquid crystalline complex has been studied using polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The chiral phases observed in the present complex are due to the presence of lone pair (n) to anti-bonding ([Formula: see text]) transition symmetry which is validated by DFT studies. A noteworthy observation of induced smectic A[Formula: see text](Sm A[Formula: see text]) by quenching of traditional phase (nematic) has been identified and the reason for the same has been discussed by DFT studies. The unusual phase order of Sm A[Formula: see text], smectic C[Formula: see text](Sm C[Formula: see text]) and smectic G[Formula: see text][Formula: see text](Sm G[Formula: see text]) mesogenic phases are observed. The other liquid crystalline parameters are evaluated by experimental and theoretical calculations and the same has been compared. Increased tilt angle in liquid crystal (LC) molecules has been theoretically analyzed by natural bond orbital (NBO) studies. Stability of the HBFLC phases and its origination mechanism have been discussed with the help of highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) energies.

Uv Curable Liquid Crystals and Their Application

1996 ◽  
Vol 425 ◽  
Author(s):  
H. Takatsu ◽  
H. Hasebe
Keyword(s):  
Liquid Crystals ◽  
Light Scattering ◽  
Liquid Crystalline ◽  
Room Temperature ◽  
Polymer Network ◽  
Driving Voltage ◽  
Uv Curable ◽  
Good Thermal Stability ◽  
Photo Polymerization ◽  
Smectic A

AbstractSome classes of liquid crystalline monoacrylates having no methylene spacers in a side chain have been prepared. The liquid crystalline monoacrylates have effects to reduce the driving voltage and the hysteresis for a light scattering display of Polymer Network liquid crystals prepared by photo-polymerization-induced phase separation.By photo-polymerization of a chiral monoacrylate monomer in a nematic liquid crystalline host including a black dichroic dye, a polarizer free reflective Spiral Polymer Aligned Nematic (SPAN) Guest Host (GH) LCD exhibiting a low driving voltage has been fabricated. The effect of the spiral polymers made of some kinds of chiral monoacrylates for a Super Twisted Nematic (STN) LCD using SPAN liquid crystals is discussed.UV-curable liquid crystals showing nematic phases at room temperature have been developed. By in situ photo-polymerization, the UV-curable liquid crystals can be utilized for the retardation film with high quality and good thermal stability. The fabrication of various kinds of retardation film using the UV-curable liquid crystals is discussed.UV-curable liquid crystals having isotropic-nematic-smectic A phase sequence have been developed and the photo-polymerization at the state of their uniaxially oriented smectic A phases at room temperature is discussed. The polymerized film is optically uniaxial and transparent without light scattering.

Electro-optic characteristics of de Vries tilted smectic liquid crystals: Analog behavior in the smectic A* and smectic C* phases

2002 ◽  
Vol 80 (22) ◽  
pp. 4097-4099 ◽  
Author(s):  
N. A. Clark ◽  
T. Bellini ◽  
R.-F. Shao ◽  
D. Coleman ◽  
S. Bardon ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Smectic Liquid Crystals ◽  
Smectic A ◽  
Smectic C ◽  
Electro Optic ◽  
De Vries ◽  
Analog Behavior

Electron Nuclear Double Resonance (ENDOR) Investigations of Organic Doublet Radicals in the Nematic and Smectic Phase of Liquid Crystals

1980 ◽  
Vol 34 (3) ◽  
pp. 305-310 ◽  
Author(s):  
B. Kirste ◽  
H. Kurreck
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Hyperfine Interactions ◽  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Smectic A ◽  
Smectic Phases ◽  
Anisotropic Hyperfine ◽  
Different Types ◽  
Nematic Phases

Different types of organic doublet radicals have been investigated in isotropic, nematic, and smectic phases of liquid crystals by performing electron nuclear double resonance (ENDOR), general TRIPLE and special TRIPLE experiments. For this purpose phenalenyls (perinaphthenyls), galvinoxyl, tetra- tert.-butylcarbazolyl, and bis(biphenylenyl)propenyl radicals have been chosen including some partially deuterated and 13C-labeled compounds. Anisotropic hyperfine interactions and deuterium quadrupole couplings could be determined. Smectic A phases have proved to be advantageous as compared to nematic phases in these studies. Detailed information about the orientation of the radicals within the liquid-crystalline solvent and about the conformations of the radicals could be obtained.

Two-Dimensional Superlattice Self-Formed by Novel Ionic Liquid Crystals and Its Photofunctional Property

1999 ◽  
Vol 559 ◽  
Author(s):  
A. Kanazawa ◽  
T. Ikeda
Keyword(s):  
Liquid Crystals ◽  
Crystalline Phase ◽  
Liquid Crystalline ◽  
Chloride Ions ◽  
Liquid Crystalline Phase ◽  
Two Dimensional ◽  
Phosphonium Salts ◽  
Smectic A ◽  
Transition Behavior ◽  
Smectic A Phase

ABSTRACTThermotropic liquid-crystalline behavior of various complex salts, which are structurally simple amphiphiles without rigid cores, was evaluated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. The phosphonium salts, consisting of positive phosphorus and negative chloride ions, were found to show a smectic A phase in which a homeotropic structure was formed spontaneously. It is significant that the phosphonium salts possess an advantageous feature as thermotropic liquid crystals and show a stable liquid-crystalline phase and a simple phase transition behavior in comparison with commonly available ammonium analogs. Furthermore, the introduction of divalent metal ions into the amphiphiles was revealed to result in enhancement of the thermal properties. Although the ammonium chlorides as parent compounds showed no liquid-crystalline phase (or indistinct transition behavior), the ammonium complexes possessing tetrachlorometalate ions exhibited clearly the smectic A phase in the expanded temperature range. Additionally, through the evaluation of dipolar alignment in the solid-state phosphonium assembly by second harmonic generation, it was assumed that the self-assembly can be regarded as layered polar thin films produced by two-dimensional ionic layers with an overall permanent electric polarization.

Design and electro-optic investigations of de Vries chiral smectic liquid crystals for exhibiting broad temperature ranges of SmA* and SmC* phases and fast electro-optic switching

2020 ◽  
Vol 8 (14) ◽  
pp. 4859-4868 ◽  
Author(s):  
V. Swaminathan ◽  
V. P. Panov ◽  
A. Panov ◽  
D. Rodriguez-Lojo ◽  
P. J. Stevenson ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Alkyl Chain ◽  
Smectic Liquid Crystals ◽  
Switching Speed ◽  
Temperature Range ◽  
Electro Optic ◽  
De Vries ◽  
Temperature Ranges

Two new ferroelectric liquid crystalline compounds using 5-phenyl-pyrimidine core terminated by achiral trisiloxane chain, and chiral (S) alkyl chain on the opposite ends of their respective mesogens are designed with better characteristics of switching speed and broader temperature range.

scholarly journals Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen

Crystals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1110
Author(s):  
Abir Aouini ◽  
Maurizio Nobili ◽  
Edouard Chauveau ◽  
Philippe Dieudonné-George ◽  
Gauthier Damême ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystal ◽  
Liquid Crystalline ◽  
Smectic A ◽  
Liquid Crystalline Phases ◽  
Electro Optic ◽  
Optical Dielectric

Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.

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