scholarly journals Orientational order of motile defects in active nematics

2015 ◽  
Vol 14 (11) ◽  
pp. 1110-1115 ◽  
Author(s):  
Stephen J. DeCamp ◽  
Gabriel S. Redner ◽  
Aparna Baskaran ◽  
Michael F. Hagan ◽  
Zvonimir Dogic
Keyword(s):  
Orientational Order

Bond-orientational order in liquid aluminium80-transition metal20 alloys

1993 ◽  
Vol 3 (8) ◽  
pp. 1873-1888 ◽  
Author(s):  
M. Maret ◽  
F. Lançon ◽  
L. Billard
Keyword(s):  
Orientational Order ◽  
Bond Orientational Order

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.

Fatty acyl chain structure, orientational order, and the lipid phase transition in Acholeplasma laidlawii B membranes. A review of recent 19F nuclear magnetic resonance studies

1984 ◽  
Vol 62 (11) ◽  
pp. 1134-1150 ◽  
Author(s):  
P. M. Macdonald ◽  
B. D. Sykes ◽  
R. N. McElhaney
Keyword(s):  
Phase Transition ◽  
Fatty Acids ◽  
Nuclear Magnetic Resonance ◽  
Acyl Chain ◽  
Orientational Order ◽  
Membrane Lipid ◽  
Fatty Acyl ◽  
Fatty Acyl Chain ◽  
Lipid Phase ◽  
Lipid Phase Transition

The orientational order parameters of monofluoropalmitic acids biosynthetically incorporated into membranes of Acholeplasma laidlawii B in the presence of a large excess of a variety of structurally diverse fatty acids have been determined via 19F nuclear magnetic resonance (19F NMR) spectroscopy. It is demonstrated that these monofluoropalmitic acids are relatively nonperturbing membrane probes based upon physical (differential scanning calorimetry), biochemical (membrane lipid analysis), and biological (growth studies) criteria. 19F NMR is shown to convey the same qualitative and quantitative picture of membrane lipid order provided by 2H-NMR techniques and to be sensitive to the structural characteristics of the membrane fatty acyl chains, as well as to the lipid phase transition. Representatives of each naturally occurring class of fatty acyl chain structures, including straight-chain saturated, methyl-branched, monounsaturated, and alicyclic-ring-substituted fatty acids, were studied and the 19F-NMR order parameters were correlated with the lipid phase transitions (determined calorimetrically). The lipid phase transition was the prime determinant of overall orientational order regardless of fatty acid structure. Effects upon orientational order attributable to specific structural substituents were discernible, but were secondary to the effects of the lipid phase transition. In the gel state, relative overall order was directly proportional to the temperature of the particular lipid phase transition. Not only the overall order, but also the order profile across the membrane was sensitive to the presence of particular structural substituents. In particular, in the gel state specific fatty acyl structures demonstrated a characteristic disordering effect in the membrane order profile. These various observations can be merged to provide a unified picture of the manner in which fatty acyl chain chemistry modulates the physical state of membrane lipids.

A chiral–racemic lyotropic chromonic liquid crystal system

Soft Matter ◽  
2021 ◽  
Author(s):  
Jordan K. Ando ◽  
Peter J. Collings
Keyword(s):  
Liquid Crystal ◽  
Optical Microscopy ◽  
Orientational Order ◽  
Molecular Assemblies ◽  
Polarized Optical Microscopy ◽  
Crystal System ◽  
System P ◽  
Liquid Crystal System

A lyotropic chromonic liquid crystal consists of oriented molecular assemblies in solution. If the molecules are chiral, the helical pattern of orientational order is revealed by the stripes seen with polarized optical microscopy.

scholarly journals The interplay between spatial and heliconical orientational order in twist-bend nematic materials

2021 ◽  
Vol 23 (7) ◽  
pp. 4055-4063
Author(s):  
R. Saha ◽  
C. Feng ◽  
C. Welch ◽  
G. H. Mehl ◽  
J. Feng ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Correlation Length ◽  
Orientational Order ◽  
Smectic Phase ◽  
Sulfur Containing

In sulfur containing liquid crystal dimers we find that at the transition to the NTB phase the positional correlation length drops. The nanoscale periodicity was also observed in the upper range of a smectic phase that forms below the NTB state.

scholarly journals Liquid Crystal Ordering in the Hexagonal Phase of Rod-Coil Diblock Copolymers

Polymers ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1262
Author(s):  
Mikhail A. Osipov ◽  
Maxim V. Gorkunov ◽  
Alexander A. Antonov
Keyword(s):  
Liquid Crystal ◽  
Order Parameter ◽  
Density Functional ◽  
Diblock Copolymers ◽  
Microphase Separation ◽  
Hexagonal Phase ◽  
Orientational Order ◽  
Order Parameters ◽  
Copolymer Composition ◽  
Rigid Rod

Density functional theory of rod-coil diblock copolymers, developed recently by the authors, has been generalised and used to study the liquid crystal ordering and microphase separation effects in the hexagonal, lamellar and nematic phases. The translational order parameters of rod and coil monomers and the orientational order parameters of rod-like fragments of the copolymer chains have been determined numerically by direct minimization of the free energy. The phase diagram has been derived containing the isotropic, the lamellar and the hexagonal phases which is consistent with typical experimental data. The order parameter profiles as functions of temperature and the copolymer composition have also been determined in different anisotropic phases. Finally, the spatial distributions of the density of rigid rod fragments and of the corresponding orientational order parameter in the hexagonal phase have been calculated.

Line broadening in the electron resonance spectra of spin probes dissolved in anisotropic media: the effect of nuclear spin quantization

1977 ◽  
Vol 353 (1672) ◽  
pp. 87-102 ◽  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nuclear Spin ◽  
Dynamic Properties ◽  
Orientational Order ◽  
Anisotropic Media ◽  
Approximate Theory ◽  
Spin Probes ◽  
Line Broadening ◽  
Electron Resonance

The line broadening in the electron resonance spectra of monoradicals dissolved in anisotropic media, such as liquid crystals, provides a valuable probe of both the orientational order and the molecular dynamics. However, the fast-motion relaxation theory employed to extract this information from the linewidths assumes that the nuclear spin is quantized along the direction of the magnetic field. This approximation is only correct when the symmetry axis of a uniaxial liquid crystal is either parallel or perpendicular to the field. We have therefore removed this assumption and have developed a general theory of line broadening valid for all orientations of the liquid crystal. The theory is then used to evaluate the angular dependence of the linewidths and this is compared with the dependence predicted by the approximate theory, for two classes of nitroxide spin probes. These comparisons reveal that for steroidal spin probes the error, introduced by assuming the nuclear spin to be quantized along the field, is confined to the dynamic properties derived from the linewidths. In contrast, significant errors appear in both the dynamic and static properties obtained from an analysis of the linewidth variations for fatty acid spin probes based on the approximate theory. It would seem that the exact theory must be employed to obtain precise information from linewidth investigations of liquid crystals, except when the orientational order is extremely small.

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