scholarly journals Formation of smectic phases in binary liquid crystal mixtures with a huge length ratio

2012 ◽  
Vol 8 ◽  
pp. 1118-1125 ◽  
Author(s):  
Nadia Kapernaum ◽  
Friederike Knecht ◽  
C Scott Hartley ◽  
Jeffrey C Roberts ◽  
Robert P Lemieux ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Liquid Crystalline ◽  
Smectic Phase ◽  
Length Ratio ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Molecular Length

A system of two liquid-crystalline phenylpyrimidines differing strongly in molecular length was studied. The phase diagram of these two chemically similar mesogens, with a length ratio of 2, was investigated, and detailed X-ray diffraction and electrooptical measurements were performed. The phase diagram revealed a destabilization of the nematic phase, which is present in the pure short compound, while the smectic state was stabilized. The short compound forms smectic A and smectic C phases, whereas the longer compound forms a broad smectic C phase and a narrow higher-ordered smectic phase. Nevertheless, in the mixtures, the smectic C phase is destabilized and disappears rapidly, whereas smectic A is the only stable phase observed over a broad concentration range. In addition, the smectic translational order parameters as well as the tilt angles of the mixtures are reduced. The higher-ordered smectic phase of the longer mesogen was identified as a smectic F phase.

scholarly journals Molecular length distribution and the formation of smectic phases

2009 ◽  
Vol 5 ◽  
Author(s):  
Nadia Kapernaum ◽  
C Scott Hartley ◽  
Jeffrey C Roberts ◽  
Robert P Lemieux ◽  
Frank Giesselmann
Keyword(s):  
Nematic Phase ◽  
Length Distribution ◽  
Stable Phase ◽  
General Interest ◽  
Structure And Dynamics ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Molecular Length ◽  
Smectic A Phase

The phase diagrams of two mixtures of chemically similar smectogenic mesogens strongly differing in molecular length were investigated. In these mixtures the nematic phase present in the pure short mesogen disappeared rapidly on the addition of the longer mesogen, while the smectic state was preserved. In the smectic state the smectic A phase was the much more stable phase as the smectic C phase disappeared quite rapidly as well. In these compounds the loss of the smectic C phase is accompanied by a decrease in smectic translational order and very small tilt angles. This leads to a concentration induced smectic C to smectic A transition. Thus smectic A seems to be the most stable phase to accommodate mesogenic molecules of substantially different length. These surprising results are of general interest for the understanding of the structure and dynamics of smectic phases, as the structure of these bidisperse smectics is signified by extensive out-of-layer fluctuations.

scholarly journals Ferroelektrische Cholesterin-Derivate

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1205-1210
Author(s):  
V. Vill ◽  
J. Thiem
Keyword(s):  
Liquid Crystalline ◽  
Crystalline Phases ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Liquid Crystalline Phases ◽  
Esterification Reactions

Abstract The feature of liquid crystalline phases of p-alkoxybenzoyloxycholesterins was elucidated. In addition to blue, cholesteric and smectic A phases also monotropic, ferroelectric smectic C phases were detected. p-Alkoxybenzoic anhydrides obtained as side products in esterification reactions show highly ordered smectic phases which resemble those of the isosteric propanediones.

Study of High Frequency Relaxation Processes in Three Substances with the -CN Groups at the Lateral Positions

2000 ◽  
Vol 55 (8) ◽  
pp. 733-740
Author(s):  
Stanisław Urban ◽  
Bo Gestbloma ◽  
Roman Dąbrowskib ◽  
Jerzy Dziaduszekb
Keyword(s):  
Relaxation Process ◽  
High Frequency ◽  
Liquid Crystalline ◽  
Activation Barrier ◽  
Relaxation Processes ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Frequency Relaxation ◽  
Cyano Groups

Abstract Three liquid crystalline (LC) substances with the cyano-groups attached at the lateral positions to the molecular cores were studied with the aid of dielectric spectroscopy methods. The high frequency relaxation process connected with the molecular reorientations around the long molecular axes was studied in the isotropic, nematic and several smectic phases. The dielectric spectra are rather complex, indicating a contribution from several molecular processes to the main relaxation process. The dielectric time changes smoothly at the phase transitions between "liquid-like" phases (isotropic -nematic -smectic A -smectic C), and becomes shorter at the transition to the "solid-like" smectic G phase with a low-ering of the activation barrier. This indicates that the molecules perform broad angle librational motions rather than overall rotational motions in this phase. In case of a substance having two cyano groups at-tached to the benzene ring, a pronounced jump-wise change of the relaxation time was observed at the isotropic -smectic A transition.

Freeze-fracture TEM of the helical smectic A* phase

1992 ◽  
Vol 50 (1) ◽  
pp. 278-279
Author(s):  
K.J. Ihn ◽  
R. Pindak ◽  
J. A. N. Zasadzinski
Keyword(s):  
Liquid Crystal ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Freeze Fracture ◽  
Smectic Phase ◽  
Layer Spacing ◽  
Screw Dislocations ◽  
Smectic A ◽  
Smectic Phases ◽  
Discrete Amount

A new liquid crystal (called the smectic-A* phase) that combines cholesteric twist and smectic layering was a surprise as smectic phases preclude twist distortions. However, the twist grain boundary (TGB) model of Renn and Lubensky predicted a defect-mediated smectic phase that incorporates cholesteric twist by a lattice of screw dislocations. The TGB model for the liquid crystal analog of the Abrikosov phase of superconductors consists of regularly spaced grain boundaries of screw dislocations, parallel to each other within the grain boundary, but rotated by a fixed angle with respect to adjacent grain boundaries. The dislocations divide the layers into blocks which rotate by a discrete amount, Δθ, given by the ratio of the layer spacing, d, to the distance between grain boundaries, lb; Δθ ≈ d/lb (Fig. 1).

scholarly journals Hexakis(terthiophenylthio)benzene as a Mew Class Liquid Crystalline Molecule

1999 ◽  
Vol 23 (10) ◽  
pp. 596-597
Author(s):  
Shinobu Inoue ◽  
Shoji Nishiguchi ◽  
Satoshi Murakami ◽  
Yoshio Aso ◽  
Tetsuo Otsubo ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Smectic A ◽  
Smectic C ◽  
Nematic Phases

A disk-like molecule, in which six α-linked terthiophenes are connected to a central benzene core via a thioether linkage, shows a sequence of calamitic liquid crystalline mesomorphism involving smectic C, smectic A and nematic phases.

scholarly journals Molecular dynamics simulation of α-unsubstituted oligo-thiophenes: dependence of their high-temperature liquid-crystalline phase behaviour on molecular length

2019 ◽  
Vol 7 (32) ◽  
pp. 9984-9995 ◽  
Author(s):  
Flora D. Tsourtou ◽  
Stavros D. Peroukidis ◽  
Vlasis G. Mavrantzas
Keyword(s):  
Molecular Dynamics ◽  
Phase Diagram ◽  
High Temperature ◽  
Molecular Dynamics Simulation ◽  
Liquid Crystalline ◽  
Md Simulations ◽  
Phase Behaviour ◽  
Dynamics Simulation ◽  
Molecular Length ◽  
Temperature Liquid

Phase diagram of α-nT oligomers with n = 5–8 from the MD simulations.

Thermal and photo optical properties of azoxybenzene/alkyloxy-azobenzene–cholesterol dimesogens with alkyl diacetylene linker

2005 ◽  
Vol 20 (12) ◽  
pp. 3431-3438 ◽  
Author(s):  
Subramanian Kumaresan ◽  
V. Ajay Mallia ◽  
Yoshishige Kida ◽  
Nobuyuki Tamaoki
Keyword(s):  
Optical Properties ◽  
Liquid Crystalline ◽  
Visible Region ◽  
Blue Shift ◽  
Isotropic Phase ◽  
Benzene Derivatives ◽  
Smectic A ◽  
Smectic Phases ◽  
Reflected Light ◽  
Liquid Crystalline Material

Thermal and photo-optical properties of azoxybenzene/alkyloxy-azobenzene containing chiral dimesogens are presented. Alkyloxyazobenzene containing dimesogenic materials exhibited two kinds of smectic A phases. Photoirradiation at temperatures exhibiting smectic phases of pure materials in azobenzene linked dimesogens resulted in formation of the isotropic phase, and this was systematically studied at different liquid crystalline temperatures. The efficacy of these compounds as a dopant in the glassy liquid crystalline material was also explored. Increasing concentration to 4 wt%/5 wt% in azobenzene/azoxy-benzene derivatives caused a dramatic red-shift in the wavelength of reflected light by the host cholesteric glassy liquid crystal. Photo-isomerization of these dopants led to a blue-shift of the reflected light, and this effect could be used to tune the light reflectivity of these mixtures over the visible region.

Phase diagram exhibiting a smectic-A–smectic-C–smectic-Fmeeting point

1992 ◽  
Vol 46 (2) ◽  
pp. R726-R728 ◽  
Author(s):  
V. N. Raja ◽  
D. S. Shankar Rao ◽  
S. Krishna Prasad
Keyword(s):  
Phase Diagram ◽  
Smectic A ◽  
Smectic C

Structural studies of nematic and smectic phases

1983 ◽  
Vol 309 (1507) ◽  
pp. 145-153 ◽  
Keyword(s):  
Liquid Crystal ◽  
Mean Field ◽  
Structural Studies ◽  
X Ray ◽  
Smectic A ◽  
Smectic C ◽  
X Ray Scattering ◽  
Smectic Phases ◽  
Crystal Phases ◽  
Field Behaviour

The information about liquid crystal phases that can be obtained by light scattering and by high-resolution X-ray scattering is reviewed. Results for the nematic-smectic A transition suggest the de Gennes-McMillan model is correct, but adequate theoretical solutions to the model remain elusive. Recent results on the smectic A to smectic C transition are presented that show unambiguously that it exhibits classic mean-field behaviour and this is explained by a Ginzburg criterion argument. Some preliminary results of a study of a nematic-smectic A transition in a lyotropic material are given and indicate similarity to thermotropic materials.

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