Defects in Degenerate Hybrid Aligned Nematic Liquid Crystals

Lavrentovich, Oleg D.; Nastishin, Yu. A.

doi:10.1209/0295-5075/12/2/008

Cited by 56 publications

(27 citation statements)

References 6 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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“…The network consists of domains formed by protrusions and troughs where the nematic director configuration is determined by the competing effects of elastic, surface, and gravity forces [7]. The similar network arose at the NI interface [8] and in hybrid ordered thin (~1 μm) nematic films with a liquid (glycerol or polyethylene glycol) surface [9]. …”

Section: Introductionmentioning

confidence: 99%

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

Parshin

Gunyakov

Zyryanov

et al. 2013

IJMS

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Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

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“…Two types of schlieren defects, simple disclination and complex disclination, in nematic have been reported. Generally, there is a simple relation between the strength S of the defects and the number N of dark brushes as lSl ¼ N=4: While the relation between the strength S and the number of the dark brushes N of complex defects is complex [17,18]. By using a quartz wedge in the polarizing microscope, it is indicated that the observed defects in our samples are simple disclinations.…”

Section: Resultsmentioning

confidence: 82%

High strength disclinations in liquid crystalline polymers with X-shaped two-dimensional mesogenic units

Zhang

2004

Polymer

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Defects in Degenerate Hybrid Aligned Nematic Liquid Crystals

Cited by 56 publications

References 6 publications

Capillary-induced giant elastic dipoles in thin nematic films

Capillary-induced giant elastic dipoles in thin nematic films

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

High strength disclinations in liquid crystalline polymers with X-shaped two-dimensional mesogenic units

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