Speeding up Dynamics by Tuning the Noncommensurate Size of Rodlike Particles in a Smectic Phase

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).

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

Scientific Reports ◽

10.1038/s41598-021-85021-y ◽

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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Model of the dynamics of an interface between a smectic phase and an isotropic phase of different density

Physical Review Fluids ◽

10.1103/physrevfluids.5.073302 ◽

2020 ◽

Vol 5 (7) ◽

Cited By ~ 1

Author(s):

Eduardo Vitral ◽

Perry H. Leo ◽

Jorge Viñals

Keyword(s):

Smectic Phase ◽

Isotropic Phase

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

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06633h ◽

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.

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