Surface Anchoring and Growth Pattern of the Field-Driven First-Order Transition in a Smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi></mml:math>Liquid Crystal

Li, Zili; Lavrentovich, Oleg D.

doi:10.1103/physrevlett.73.280

Cited by 61 publications

(31 citation statements)

References 14 publications

(18 reference statements)

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“…(C ) If the center of hemicylinder is placed under the substrate, the scheme can be described differently, and the surface energy of an off-centered hemicylinder to the air is decreased compared with that of a perfect hemicylinder. (D) If there exist walls between cylinders, the surface area of the cylinder to the air is decreased at ðπ − 2θÞR 2 and there exists a wall energy between cylinders much larger than the elastic energy of smectic cylinders.…”

Section: Discussionmentioning

confidence: 99%

“…sublime | direct visualization T he study of the structure of layered soft materials began in the early 1900s with the legendary inference of Grandjean and Friedel of the fluid layer structure of smectic liquid crystals (LCs) based on their observation of the elliptical core lines of focal conic defects and their interpretation of these as the singularities that appear when space is filled with equally spaced curved surfaces generated from the cyclides of Dupin (1)(2)(3)(4). Since that time, the techniques of X-ray diffraction, and visualization, using optical transmission and fluorescence confocal polarizing microscopy; atomic force microscopy (AFM); and SEM and transmission electron microscopy (TEM), including freeze fracture TEM (FFTEM), have been widely applied to characterize soft layering and defects (5)(6)(7)(8)(9)(10), but the ability to visualize layering directly throughout a 3D sample (e.g., in particular confinement conditions) has been limited.…”

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confidence: 99%

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Three-dimensional textures and defects of soft material layering revealed by thermal sublimation

Yoon

Kim

et al. 2013

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

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Layering is found and exploited in a variety of soft material systems, ranging from complex macromolecular self-assemblies to block copolymer and small-molecule liquid crystals. Because the control of layer structure is required for applications and characterization, and because defects reveal key features of the symmetries of layered phases, a variety of techniques have been developed for the study of soft-layer structure and defects, including X-ray diffraction and visualization using optical transmission and fluorescence confocal polarizing microscopy, atomic force microscopy, and SEM and transmission electron microscopy, including freezefracture transmission electron microscopy. Here, it is shown that thermal sublimation can be usefully combined with such techniques to enable visualization of the 3D structure of soft materials. Sequential sublimation removes material in a stepwise fashion, leaving a remnant layer structure largely unchanged and viewable using SEM, as demonstrated here using a lamellar smectic liquid crystal.sublime | direct visualization T he study of the structure of layered soft materials began in the early 1900s with the legendary inference of Grandjean and Friedel of the fluid layer structure of smectic liquid crystals (LCs) based on their observation of the elliptical core lines of focal conic defects and their interpretation of these as the singularities that appear when space is filled with equally spaced curved surfaces generated from the cyclides of Dupin (1-4). Since that time, the techniques of X-ray diffraction, and visualization, using optical transmission and fluorescence confocal polarizing microscopy; atomic force microscopy (AFM); and SEM and transmission electron microscopy (TEM), including freeze fracture TEM (FFTEM), have been widely applied to characterize soft layering and defects (5-10), but the ability to visualize layering directly throughout a 3D sample (e.g., in particular confinement conditions) has been limited. Here, we apply thermal sublimation, a technique that is widely applicable due to the relatively low vapor pressure of many soft material components, as a method for removing material from a 3D sample that maintains its internal structure (i.e., moves the material surface into the bulk, creating a deeper interface that exhibits a topography that reflects the local structure).We demonstrate this method using the thermal sublimation of a fluid smectic LC phase, wherein the LC material was removed layer by layer. We show that even in small-molecule, hightemperature fluid smectic A (SmA) phases, the underlying layer structure successfully resists surface tension (which tends to smooth out the advancing interface) to yield a surface topography that exhibits features of the underlying layer structure. Local features, such as defects, can advance or retard sublimation, leading to distinct visualization and control effects. The full 3D structure of a layered sample was exposed by successive sublimation steps and maintained during visualization by cooling. The remn...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Three-dimensional textures and defects of soft material layering revealed by thermal sublimation

Yoon

Kim

et al. 2013

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

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“…In the N TB region, the reorientation occurs at a higher voltage [7 V @ 10 KHz, Fig. 3(c)], and in the form of propagating focal-conic domains (FCDs), such as is usually observed in smectic liquid crystals with negative dielectric anisotropy [24,25]. The "pseudolayered" nature of the heliconical structure [15] is reflected in the gradual relaxation of the FCDs to homeotropic alignment after removal of the field.…”

Section: Methodsmentioning

confidence: 99%

“…(15) in the nematic phase and Eqs. (23) and (24) in the N TB phase. For the equilibrium cone angle β and pitch wave number q 0 , we use the leading terms in Eqs.…”

Section: B Twist-bend Phasementioning

confidence: 99%

Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal

et al. 2016

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We report a dynamic light-scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (N TB ) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic modes and one hydrodynamic mode in the N TB phase, and a single nonhydrodynamic mode plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-de Gennes expansion of the free-energy density in terms of heliconical director and helical polarization fields that characterize the N TB structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.

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“…Recent atomic force examination of FCDs in cholesteric oligomers by Meister et al [87] reveals smooth matching between layers tilted at the free surface of the sample (inside the FCDs) and¯at layers in the bulk that are parallel to the interface (outside the FCDs). Focal conic textures and their transformations under applied electric ®eld, studied for smectic layered systems [88], [89], are used in bistable cholesteric re¯ective displays [90].…”

Section: Focal Conic Domainsmentioning

confidence: 99%

Cholesteric Liquid Crystals: Defects and Topology

Lavrentovich¹,

Kléman²

Partially Ordered Systems

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This chapter reviews the basic static properties of defects in cholesteric liquid crystals. The elastic features of the cholesteric phase with deformations at short-range and long-range (as compared to the cholesteric pitch) scales are discussed. Spatial con®nement, together with the relative smallness of the twist elastic constant, often leads to twisted and thus optically active structures even when the liquid crystal is composed of nonchiral molecules. The application of topological methods is illustrated using the models of twisted strips, closed DNA molecules, and defect linesÐdisclinations and dislocations. The homotopy classi®cation of defects in cholesterics is similar to that in biaxial nematics, and predicts phenomena such as the topological entanglement of disclinations and the formation of nonsingular soliton con®gurations. The spatial con®nement of ordered structures (represented, for example, by cholesteric droplets suspended in an isotropic matrix) imposes certain restrictions on the con®gurations of the order parameter and requires the appearance of topological defects in the ground state. The layered structure of cholesterics leads to the formation of large-scale defects such as focal conic domains and oily streaks.

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Surface Anchoring and Growth Pattern of the Field-Driven First-Order Transition in a Smectic-ALiquid Crystal

Cited by 61 publications

References 14 publications

Three-dimensional textures and defects of soft material layering revealed by thermal sublimation

Three-dimensional textures and defects of soft material layering revealed by thermal sublimation

Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal

Cholesteric Liquid Crystals: Defects and Topology

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