Non-singular disclinations of strength S = + 1 in nematics

Cladis, P. E.; Kléman, M.

doi:10.1051/jphys:01972003305-6059100

Cited by 364 publications

(181 citation statements)

References 3 publications

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“…The two degenerate escape directions and the two degenerate senses of handedness (right/left) in the TER configuration lead to three possible types of defects for these systems: radial point defects, hyperbolic point defects, and domain walls of opposite handedness. Singular point defects (hedgehogs) have been observed previously in the common escaped radial configuration without twist, and they are located in regions where the escape direction changes (58)(59)(60)(61)(62)(63). Fig.…”

Section: Significancementioning

confidence: 93%

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Chiral structures from achiral liquid crystals in cylindrical capillaries

Jeong

Kang

Davidson

et al. 2015

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

110

103

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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 ...

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Section: Significancementioning

confidence: 93%

“…POM images of nematic SSY in capillaries with homeotropic boundary conditions exhibit features that are subtly different from those in the POM images of samples in the well-known escaped radial configuration (58)(59)(60). In the bright-field microscopy image in Fig.…”

Section: Significancementioning

confidence: 97%

Chiral structures from achiral liquid crystals in cylindrical capillaries

Jeong

Kang

Davidson

et al. 2015

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

110

103

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“…It is perhaps for this reason that it is commonplace amongst workers in liquid crystal theory to associate a line defect only with a singularity, e.g. the 'escape' solution for a +1 strength line defect [CK72] is often not referred to as a defect solution.…”

Section: Introductionmentioning

confidence: 99%

A fundamental improvement to Ericksen-Leslie kinematics

2015

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We demonstrate theory and computations for finite-energy line defect solutions in an improvement of Ericksen-Leslie liquid crystal theory. Planar director fields are considered in two and three space dimensions, and we demonstrate straight as well as loop disclination solutions. The possibility of static balance of forces in the presence of a disclination and in the absence of flow and body forces is discussed. The work exploits an implicit conceptual connection between the Weingarten-Volterra characterization of possible jumps in certain potential fields and the Stokes-Helmholtz resolution of vector fields. The theoretical basis of our work is compared and contrasted with the theory of Volterra disclinations in elasticity. Physical reasoning precluding a gauge-invariant structure for the model is also presented.

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“…[1][2][3] Cylindrical confinements, a form of symmetric confinement, have been employed to study these various structures and the properties of LCs. [4][5][6][7][8] For example, an escaped-radial configuration [9][10][11][12] and beaded-core defects [13][14][15] are observed in cylinders. In addition, the elastic constants and the anchoring energy of LCs have been determined from observation of confined LCs.…”

mentioning

confidence: 99%

“…2(a), nematic LCs have escaped-radial configurations [9][10][11] in the elliptic cylindrical confinement with homeotropic anchoring. In the POM images with crossed polarizers in a diagonal direction, we identify two broad dark lines that are observed typically in the escaped-radial configuration.…”

mentioning

confidence: 99%