Periodic stripe domains and hybrid-alignment regime in nematic liquid crystals: Threshold analysis

Sparavigna, Amelia Carolina; Lavrentovich, Oleg D.; Strigazzi, Alfredo

doi:10.1103/physreve.49.1344

Cited by 89 publications

(146 citation statements)

References 23 publications

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“…The difference in anchoring conditions Θ = θ p − θ h (Fig. 1A) leads to a continuous 3D distortion of the director n. Such hybrid anchoring nematic films (mainly studied on glycerin) have already been thoroughly examined both experimentally and theoretically (12,13,16,(19)(20)(21). Thick films are expected to show a simple and homogeneous structure in the layer plane (defining a 2D c director sketched in Fig.…”

Section: Significancementioning

confidence: 99%

Capillary-induced giant elastic dipoles in thin nematic films

Jeridi

Gharbi

Othman

et al. 2015

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

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Directed and true self-assembly mechanisms in nematic liquid crystal colloids rely on specific interactions between microparticles and the topological defects of the matrix. Most ordered structures formed in thin nematic cells are thus based on elastic multipoles consisting of a particle and nearby defects. Here, we report, for the first time to our knowledge, the existence of giant elastic dipoles arising from particles dispersed in free nematic liquid crystal films. We discuss the role of capillarity and film thickness on the dimensions of the dipoles and explain their main features with a simple 2D model. Coupling of capillarity with nematic elasticity could offer ways to tune finely the spatial organization of complex colloidal systems.A mong the various systems proposed heretofore for bottomup assemblies of solid particles, nematic liquid crystal (NLC) dispersions have attracted a lot of attention. Such systems indeed promote complex anisotropic 2D patterns that can easily resist thermal fluctuations and external perturbations (1-3). The mechanisms responsible for self-assembly in nematics are now well understood. The nematic phase is a fluid with an orientational order, in which locally the molecules spontaneously align in a common direction, the director n. The imposed orientation of the molecules at the surface of solid particles (the so-called anchoring phenomenon) creates a large-scale distortion of the field nðrÞ. Orientational elasticity, far-field alignment, and topological constraints then yield the formation of topological defects associated to the particles (4, 5). A typical system that has been extensively studied is a microsphere with a perpendicular (homeotropic) anchoring immersed in a thin planar-aligned nematic cell. Topologically equivalent to a hedgehog defect for the director field nðrÞ, the spherical particle necessarily creates other topological defects in the uniform far-field director, such as a hyperbolic hedgehog point defect or a Saturn-ring defect (a closed disclination line). The particle-defect pair forms a neutral unit and is stable contrary to a couple of true topological defects that would annihilate. The self-assembly of particles is then explained by the residual distortion of the matrix far from the pair, which yields long-range elastic interactions between particles (5, 6). Whereas the far-distance distortion can be always treated asymptotically, the local director field around the particle depends on several parameters, such as the size and shape of the inclusion or the finite strength of the anchoring, and is accessible only via numerical approaches (7). In all cases, one observes a defect located at a close distance from the particle (of order of its size). Such a scheme is found with particles of different shapes and sizes (8, 9): When introduced in a NLC, a microparticle generates elastic distortions and topological defects in its close neighborhood, i.e., at a distance comparable to its size, and we call this particle-defect pair a common short dipole.In this paper...

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Section: Significancementioning

confidence: 99%

Capillary-induced giant elastic dipoles in thin nematic films

Jeridi

Gharbi

Othman

et al. 2015

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

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“…These attract attention due to potential applications of variable grating mode (VGM) optical computing devices [2] as well as for convenient measurements of the intrinsic physical properties of liquid crystals [1]. Periodic stripe patterns easily observed by polarizing optical microscopy (POM) are normally caused by the presence of a helical structure [1] or by the application of external fields: magnetic [3], electric [4], or mechanical stress [5,6]. In planar geometry of the cell, the spontaneous deformations of nematic director have also been proposed theoretically [7][8][9][10].…”

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confidence: 99%

Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant

et al. 2010

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“…However, the term multiplied by coefficient K24 is not proper of the bulk energy, because it is a contribution to the surface energy of the material [4]. Consequently, the Frank equation for the density of the elastic energy is given by the following elemental deformations [9] …”

Section: The Elastic Deformation Of a Nematicmentioning

confidence: 99%

“…Let us evaluate its order as made for (4 Tables I-III: These three Tables are giving the contributions to the density of the free energy of a nematic liquid crystal coming from tensors N, D and H, respectively. In the second Table, contributions coming from D marked by * are those shared with N. In the third Table, contributions to the free energy density coming from H, marked by *, are shared with D, whereas those marked by ** are shared with N and D.…”

Section: Second-order Elasticity Close To a Thresholdmentioning

confidence: 99%

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Elasticity Tensors in Nematic Liquid Crystals

Sparavigna¹

2016

ijSciences

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Abstract:The paper is discussing the contributions to the free energy of elastic distortions in a nematic liquid crystal. These contributions are here given by tensors, which are represented by means of the components of the director, the unit vector indicating the local average alignment of molecules, and by Kronecker and Levi-Civita symbols. The paper is also discussing the elasticity of the second order and its contribution in threshold phenomena.

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Periodic stripe domains and hybrid-alignment regime in nematic liquid crystals: Threshold analysis

Cited by 89 publications

References 23 publications

Capillary-induced giant elastic dipoles in thin nematic films

Capillary-induced giant elastic dipoles in thin nematic films

Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant

Elasticity Tensors in Nematic Liquid Crystals

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