Effect of chirality on liquid crystals in capillary tubes with parallel and perpendicular anchoring

Kitzerow, Heinz‐S.; Liu, B.; Xu, F.; Crooker, P. P.

doi:10.1103/physreve.54.568

Cited by 49 publications

(44 citation statements)

References 17 publications

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“…This general class of configuration has been investigated in cylinders (47)(48)(49)(50)(51)(52). However, this system differs significantly from earlier work.…”

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confidence: 58%

Chiral structures from achiral liquid crystals in cylindrical capillaries

Jeong

Kang

Davidson

et al. 2015

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

109

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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“…This general class of configuration has been investigated in cylinders (47)(48)(49)(50)(51)(52). However, this system differs significantly from earlier work.…”

mentioning

confidence: 58%

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

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“…2) This has been demonstrated originally by Adams and Haas 61 quite some time ago and later by Cladis 25 and by Kitzerow et al 30 These authors argue that for fixed T, p −1 ∝ c where c is the concentration of chiral dopant in the binary mixture. Thus, by varying c, one gets a handle on p. As pointed out later by Wilson and Earl, 62 the concentration of chiral dopant is proportional to a change in free energy which in turn may be interpreted as a change in the effective strength of interaction between molecules of the chiral mixture component.…”

Section: B Bulk Systemmentioning

confidence: 78%

“…19 This has been shown experimentally quite some time ago 30 but a comprehensive theoretical understanding of the interplay between chirality and confinement is still in its infancy. For example, focusing on blue phase I confined to a slit-pore, Fukuda and Žumer use Landau-de Gennes theory to investigate novel defect structures under severe confinement.…”

Section: Introductionmentioning

confidence: 99%

Defect topologies in chiral liquid crystals confined to mesoscopic channels

Schlotthauer

Skutnik

Stieger

et al. 2015

The Journal of Chemical Physics

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We present Monte Carlo simulations in the grand canonical and canonical ensembles of a chiral liquid crystal confined to mesochannels of variable sizes and geometries. The mesochannels are taken to be quasi-infinite in one dimension but finite in the two other directions. Under thermodynamic conditions chosen and for a selected value of the chirality coupling constant, the bulk liquid crystal exhibits structural characteristics of a blue phase II. This is established through the tetrahedral symmetry of disclination lines and the characteristic simple-cubic arrangement of double-twist helices formed by the liquid-crystal molecules along all three axes of a Cartesian coordinate system. If the blue phase II is then exposed to confinement, the interplay between its helical structure, various anchoring conditions at the walls of the mesochannels, and the shape of the mesochannels gives rise to a broad variety of novel, qualitative disclination-line structures that are reported here for the first time.

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“…To this end, a linear photopolymerization technique was used to ensure a uniaxial orientation of the LC. This technique was initially applied to liquid crystal cells [27] and has proven to be applicable to capillaries as well [28]. The fiber (LMA8: d 2.27 μm, Λ 5.35 μm, made from silica, n 1.4584 at 589 nm, NKT Photonics) was cut to a length of 10-20 cm.…”

mentioning

confidence: 99%

Measurement of group velocity dispersion in a solid-core photonic crystal fiber filled with a nematic liquid crystal

Wahle

Kitzerow

2014

Opt. Lett.

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Liquid crystal-filled photonic crystal fibers (PCFs) are promising candidates for electrically tunable integrated photonic devices. In this Letter, we present group velocity measurements on such fibers. A large mode area PCF, LMA8, was infiltrated with the liquid crystal mixture, E7. The measurements were performed with an interferometric setup. The fiber exhibits several spectral transmission windows in the visible wavelength regime that originate from the bandgap guiding mechanism. The dispersion of these windows is very unusual compared to typical fibers. Our measurements show that it can change from -2500 ps km(-1) nm(-1) to +2500 ps km(-1) nm(-1) within a spectral range of only 15 nm. This leads to multiple zero dispersion wavelengths in the visible wavelength range.

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Effect of chirality on liquid crystals in capillary tubes with parallel and perpendicular anchoring

Cited by 49 publications

References 17 publications

Chiral structures from achiral liquid crystals in cylindrical capillaries

Chiral structures from achiral liquid crystals in cylindrical capillaries

Defect topologies in chiral liquid crystals confined to mesoscopic channels

Measurement of group velocity dispersion in a solid-core photonic crystal fiber filled with a nematic liquid crystal

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