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 Mosaics of topological defects in micropatterned liquid crystal textures

2018 ◽  
Vol 4 (11) ◽  
pp. eaau8064 ◽  
Author(s):  
Dae Seok Kim ◽  
Simon Čopar ◽  
Uroš Tkalec ◽  
Dong Ki Yoon
Keyword(s):  
Liquid Crystal ◽  
Orientational Order ◽  
Topological Defects ◽  
Smectic Phase ◽  
Dimensional System ◽  
Two Dimensional ◽  
Layer Spacing ◽  
Smectic A ◽  
Lattice Symmetry ◽  
Two Dimensional System

Topological defects in the orientational order that appear in thin slabs of a nematic liquid crystal, as seen in the standard schlieren texture, behave as a random quasi–two-dimensional system with strong optical birefringence. We present an approach to creating and controlling the defects using air pillars, trapped by micropatterned holes in the silicon substrate. The defects are stabilized and positioned by the arrayed air pillars into regular two-dimensional lattices. We explore the effects of hole shape, lattice symmetry, and surface treatment on the resulting lattices of defects and explain their arrangements by application of topological rules. Last, we show the formation of detailed kaleidoscopic textures after the system is cooled down across the nematic–smectic A phase transition, frustrating the defects and surrounding structures with the equal-layer spacing condition of the smectic phase.

Interaction Between Lattice Dislocations and Grain Boundaries In Ordered Compounds

1990 ◽  
Vol 213 ◽  
Author(s):  
B.J. Pestman ◽  
J. Th. M. De Hosson ◽  
V. Vitek ◽  
F.W. Schapink
Keyword(s):  
Shear Stress ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Partial Dislocation ◽  
Atomistic Simulations ◽  
Many Body ◽  
Shockley Partial Dislocation ◽  
Screw Dislocations ◽  
Applied Shear Stress ◽  
Tilt Boundaries

ABSTRACTThe interaction of 1/2<1 1 0> screw dislocations with symmetric [1 1 0] tilt boundaries was investigated by atomistic simulations using many-body potentials representing ordered compounds. The calculations were performed with and without an applied shear stress. The observations were: absorption into the grain boundary, attraction of a lattice Shockley partial dislocation towards the grain boundary and transmission through the grain boundary under the influence of a shear stress. It was found that the interaction in ordered compounds shows similarities to the interaction in fcc.

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.

TEM study on freeze-fracture structure of smectic A* phase

1991 ◽  
Vol 49 ◽  
pp. 1124-1125
Author(s):  
K J. Ihn ◽  
J. Zasadzinski ◽  
R. Pindak ◽  
J. Patel ◽  
J. Goodby
Keyword(s):  
Freeze Fracture ◽  
Helical Structure ◽  
Racemic Mixture ◽  
Helical Axis ◽  
Chiral Molecules ◽  
Helical Structures ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Axis Parallel

Liquid crystals (LCs) with chiral molecules show helical structure. The most well known LC phase having helical structure is cholesteric, in which average direction of molecular axes rotates around a helical axis, as shown in Fig. 1. Two kinds of helical structures were found in smectic phases. The smectic A* phase contains the helical axis parallel to the smectic layers, and in the smectic C* phase, it is perpendicular. The Smectic A* phase was recently discovered in 1-methylheptyl 4'-[[(tetradecyloxyphenyl)propionyl]oxy]biphenyl-4-carboxylate, (+14P1M7). +14P1M7 changes its phase from isotropic melt to A* phase at 93°C and C* phase at 89.5°C, while a racemic mixture shows the untwisted A and C phase. The structure of smectic A* phase was predicted by Renn and Lubensky by hypothesizing a Twist grain boundary (TGB) phase in analogy with the Abrikosov phase in superconductors.

Thermoreversible Contraction and Extension of Layer Spacing in Smectic Phase of Side Chain Liquid Crystal Poly(fumarate)s

2008 ◽  
Vol 29 (19) ◽  
pp. 1593-1597 ◽  
Author(s):  
Tsuyoshi Michinobu ◽  
Nozomu Fujii ◽  
Masatoshi Tokita ◽  
Junji Watanabe ◽  
Kiyotaka Shigehara
Keyword(s):  
Liquid Crystal ◽  
Smectic Phase ◽  
Side Chain ◽  
Layer Spacing

Pattern formation at the traveling liquid-crystal twist grain boundary-smectic a interface

1994 ◽  
Vol 16 (7) ◽  
pp. 765-770 ◽  
Author(s):  
P. E. Cladis ◽  
A. J. Slaney ◽  
J. W. Goodby ◽  
H. R. Brand
Keyword(s):  
Liquid Crystal ◽  
Pattern Formation ◽  
Grain Boundary ◽  
Smectic A

Structure of Grain Boundaries in Metals and Alloys: Direct Observations in the TEM

1973 ◽  
Vol 31 ◽  
pp. 106-107
Author(s):  
L. E. Murr
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Small Angle ◽  
Structural Features ◽  
Metals And Alloys ◽  
Boundary Structure ◽  
Screw Dislocations ◽  
Direct Observations ◽  
Grain Boundary Structure

Many models of grain boundaries in metals and alloys have been developed in attempts to interpret their properties and observed structures. Because of the complexity of grain boundary structure, it is generally possible to apply any of the proposed models in any material, and to describe grain boundaries as possessing dislocation structures, ledges, protrusions, island structures, facets, coincidence regions which exhibit good atomic fit and establish a kind of superlattice array, and combinations of these structural features.The dislocation nature of small angle grain boundaries is well known, consisting of tilt or twist arrays or combinations of edge or screw dislocations.

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.

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