Optical determination of the saddle-splay elastic constant<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="italic">K</mml:mi></mml:mrow><mml:mrow><mml:mn>24</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>in nematic liquid crystals

Polak, Robert D.; Crawford, G. P.; Kostival, B. C.; Doane, J. William; Žumer, S.

doi:10.1103/physreve.49.r978

Cited by 101 publications

(91 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Additional study of LCLCs in a cylindrical geometry will enable us to investigate unexplored properties of LCLCs, such as the saddlesplay modulus (65,66), and also, develop applications using chiral structures. For example, we should be able to study chiral amplification by splitting the chiral degeneracy or imprinting a certain handedness (67,68).…”

Section: Resultsmentioning

confidence: 99%

Chiral structures from achiral liquid crystals in cylindrical capillaries

Jeong

Kang

Davidson

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

109

103

View full text Add to dashboard Cite

We study chiral symmetry-broken configurations of nematic liquid crystals (LCs) confined to cylindrical capillaries with homeotropic anchoring on the cylinder walls (i.e., perpendicular surface alignment). Interestingly, achiral nematic LCs with comparatively small twist elastic moduli relieve bend and splay deformations by introducing twist deformations. In the resulting twisted and escaped radial (TER) configuration, LC directors are parallel to the cylindrical axis near the center, but to attain radial orientation near the capillary wall, they escape along the radius through bend and twist distortions. Chiral symmetry-breaking experiments in polymercoated capillaries are carried out using Sunset Yellow FCF, a lyotropic chromonic LC with a small twist elastic constant. Its director configurations are investigated by polarized optical microscopy and explained theoretically with numerical calculations. A rich phenomenology of defects also arises from the degenerate bend/twist deformations of the TER configuration, including a nonsingular domain wall separating domains of opposite twist handedness but the same escape direction and singular point defects (hedgehogs) separating domains of opposite escape direction. We show the energetic preference for singular defects separating domains of opposite twist handedness compared with those of the same handedness, and we report remarkable chiral configurations with a double helix of disclination lines along the cylindrical axis. These findings show archetypally how simple boundary conditions and elastic anisotropy of confined materials lead to multiple symmetry breaking and how these broken symmetries combine to create a variety of defects.mirror symmetry | parity symmetry | topological defects | chiral defects T he emergence of chirality from achiral systems poses fundamental questions about which we have limited mechanistic understanding (1-11). When the chiral symmetry of an achiral system is broken, a handedness is established, and materials with different handedness commonly exhibit distinct and useful properties (10-14) relevant for applications ranging from chemical sensors (15, 16) to photonics (17-19). To date, considerable effort has been expended to control handedness in materials (for example, by chiral separation of racemic mixtures or chiral amplification of small enantiomeric imbalances) (1,8,(20)(21)(22). Recently and in a different vein, identification and elucidation of pathways by which achiral building blocks spontaneously organize to create chiral structures have become an area of active study. Examples of these pathways include packing with multiple competing length scales (8-10, 23, 24), reconfiguration through mechanical instabilities of periodic structures (20,25,26), and helix formation of flexible cylinders through inter-and intracylinder interactions (27,28). In addition, the system of a broken chiral symmetry often consists of domains of opposite handedness with defects separating the domains.Liquid crystals (LCs) are soft materials composed ...

show abstract

Section: Resultsmentioning

confidence: 99%

Chiral structures from achiral liquid crystals in cylindrical capillaries

Jeong

Kang

Davidson

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

109

103

View full text Add to dashboard Cite

show abstract

“…A study of the nature of the elastic constants in the nematic phase of our material has shown that this mesogen possesses relatively low splay, twist and bend elastic constants (K 11 = 8 pN, K 22 = 1 pN, K 33 = 3 pN close to N-DC phase transition) [33,34]. The standard elastic approach predicts that the saddle-splay elastic constant K 24 ≤ 2K 11 + K 22 or K 24 < K 22 whichever is smaller [39][40][41]. Also, the experiments carried out on the Kerr constant, K of this material in the DC phase indicate a low value for K (<10 -11 m/V 2 ) [42] in the phase.…”

Section: Discussionmentioning

confidence: 99%

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

et al. 2014

View full text Add to dashboard Cite

Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarizing optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system: On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 µm to 15 µm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/µm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.

show abstract

“…A study of the nature of the elastic constants in the nematic phase of our material has shown that this mesogen possesses relatively low splay, twist and bend elastic constants (K11 = 8 pN, K22 = 1 pN, K33 = 3 pN close to N-DC phase transition) [35,36]. The standard theoretical elastic approach predicts that the saddle-splay elastic constant K24 ≤ 2K11 + K22 or K24 < K22 whichever is smaller [48][49][50]. Therefore, the absence of a field-induced complete deformation of the sponge-like structure of the DC phase of our material could be because of the possibility of more highly negative K24 elastic constant in this material.…”

Section: E-field Induced Changes and Molecular Reorientation Mechanismsmentioning

confidence: 99%

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

et al. 2015

View full text Add to dashboard Cite

The dark conglomerate phase exhibited by a bent-core liquid crystal material shows remarkable properties including an electric-field tuneable chiral domain structure and a large (0.045) reduction of refractive index, while maintaining an optically dark texture when observed under crossed polarisers. A detailed investigation of the system is presented, leading to a model that is fully consistent with the experimental observations. It reports the observation of two distinct regimes in the DC phase: a higher temperature regime in which the periodicity measured by small angle X-ray scattering decreases slightly (0.5%) and a lower temperature regime where it increases considerably (16%). Also, the paper discusses the unusual electric field-induced transformations observed in both the regimes. These changes have threshold fields that are both temperature and frequency dependent, though the phenomena are observed irrespective of device thickness, geometry and the alignment layer. The electro-optic behaviour in the DC phase correspond to a number of structural changes leading to unusual changes in physical properties including small (1%) increase in periodicity and a doubling of the average dielectric permittivity. We propose a model of the DC phase where in the ground state the nanostructure of phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.2

show abstract

Optical determination of the saddle-splay elastic constantK24in nematic liquid crystals

Cited by 101 publications

References 25 publications

Chiral structures from achiral liquid crystals in cylindrical capillaries

Chiral structures from achiral liquid crystals in cylindrical capillaries

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Understanding the unusual reorganization of the nanostructure of a dark conglomerate phase

Contact Info

Product

Resources

About