scholarly journals Elementary Edge and Screw Dislocations Visualized at the Lattice Periodicity Level in the Smectic Phase of Colloidal Rods

2018 ◽  
Vol 121 (9) ◽  
Author(s):  
Andrii Repula ◽  
Eric Grelet
Keyword(s):  
Smectic Phase ◽  
Screw Dislocations ◽  
Lattice Periodicity ◽  
Colloidal Rods

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).

Deviations from Ideal Decagonal Symmetry in Electron Diffraction Patterns of the “Decagonal” Phase in the Al-Co-Cu Alloy System

1991 ◽  
Vol 49 ◽  
pp. 914-915
Author(s):  
Atul S. Ramani ◽  
Earle R. Ryba ◽  
Paul R. Howell
Keyword(s):  
Electron Microscope ◽  
Alloy System ◽  
Nominal Composition ◽  
Dimensional Lattice ◽  
3 Dimensional ◽  
Decagonal Phase ◽  
Cu Alloy ◽  
Transmission Electron ◽  
Lattice Periodicity ◽  
Diffraction Patterns

The “decagonal” phase in the Al-Co-Cu system of nominal composition Al65CO15Cu20 first discovered by He et al. is especially suitable as a topic of investigation since it has been claimed that it is thermodynamically stable and is reported to be periodic in the dimension perpendicular to the plane of quasiperiodic 10-fold symmetry. It can thus be expected that it is an important link between fully periodic and fully quasiperiodic phases. In the present paper, we report important findings of our transmission electron microscope (TEM) study that concern deviations from ideal decagonal symmetry of selected area diffraction patterns (SADPs) obtained from several “decagonal” phase crystals and also observation of a lattice of main reflections on the 10-fold and 2-fold SADPs that implies complete 3-dimensional lattice periodicity and the fundamentally incommensurate nature of the “decagonal” phase. We also present diffraction evidence for a new transition phase that can be classified as being one-dimensionally quasiperiodic if the lattice of main reflections is ignored.

In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

1975 ◽  
Vol 33 ◽  
pp. 58-59
Author(s):  
F. H. Louchet ◽  
L. P. Kubin
Keyword(s):  
Electron Microscope ◽  
Transition Temperature ◽  
Low Temperature ◽  
Slip System ◽  
Low Temperatures ◽  
Tensile Axis ◽  
Image Intensifier ◽  
Screw Dislocations ◽  
Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

Screw dislocations on $\left\{1\bar{2}12\right\}$ pyramidal planes induced by Vickers indentation in HVPE GaN

2020 ◽  
Vol 59 (9) ◽  
pp. 091005
Author(s):  
Yukari Ishikawa ◽  
Yoshihiro Sugawara ◽  
Daisaku Yokoe ◽  
Yongzhao Yao
Keyword(s):  
Vickers Indentation ◽  
Screw Dislocations

scholarly journals Strain-induced variant selection in heterogeneous nucleation of α -Ti at screw dislocations in β -Ti

2018 ◽  
Vol 2 (8) ◽  
Author(s):  
Max Poschmann ◽  
Joseph Lin ◽  
Henry Geerlings ◽  
Ian S. Winter ◽  
D. C. Chrzan
Keyword(s):  
Heterogeneous Nucleation ◽  
Variant Selection ◽  
Screw Dislocations

scholarly journals Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Debashis Majhi ◽  
Sergey V. Dvinskikh
Keyword(s):  
Ionic Liquid ◽  
Ionic Liquids ◽  
Liquid Crystals ◽  
Bond Order ◽  
Van Der Waals ◽  
Orientational Order ◽  
Smectic Phase ◽  
Side Chains ◽  
Dicationic Ionic Liquid ◽  
Ionic Liquid Crystals

AbstractIonic liquids crystals belong to a special class of ionic liquids that exhibit thermotropic liquid-crystalline behavior. Recently, dicationic ionic liquid crystals have been reported with a cation containing two single-charged ions covalently linked by a spacer. In ionic liquid crystals, electrostatic and hydrogen bonding interactions in ionic sublayer and van der Waals interaction in hydrophobic domains are the main forces contributing to the mesophase stabilization and determining the molecular orientational order and conformation. How these properties in dicationic materials are compared to those in conventional monocationic analogs? We address this question using a combination of advanced NMR methods and DFT analysis. Dicationic salt 3,3′-(1,6-hexanediyl)bis(1-dodecylimidazolium)dibromide was studied. Local bond order parameters of flexible alkyl side chains, linker chain, and alignment of rigid polar groups were analyzed. The dynamic spacer effectively “decouples” the motion of two ionic moieties. Hence, local order and alignment in dicationic mesophase were similar to those in analogous single-chain monocationic salts. Bond order parameters in the side chains in the dicationic smectic phase were found consistently lower compared to double-chain monocationic analogs, suggesting decreasing contribution of van der Waals forces. Overall dication reorientation in the smectic phase was characterized by low values of orientational order parameter S. With increased interaction energy in the polar domain the layered structure is stabilized despite less ordered dications. The results emphasized the trends in the orientational order in ionic liquid crystals and contributed to a better understanding of interparticle interactions driving smectic assembly in this and analogous ionic mesogens.

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