scholarly journals Topological defects, orientational order, and depinning of the electron solid in a random potential

1994 ◽  
Vol 50 (19) ◽  
pp. 14368-14380 ◽  
Author(s):  
Min-Chul Cha ◽  
H. A. Fertig
Keyword(s):  
Random Potential ◽  
Orientational Order ◽  
Topological Defects

scholarly journals Topology control of human fibroblast cells monolayer by liquid crystal elastomer

2020 ◽  
Vol 6 (20) ◽  
pp. eaaz6485 ◽  
Author(s):  
Taras Turiv ◽  
Jess Krieger ◽  
Greta Babakhanova ◽  
Hao Yu ◽  
Sergij V. Shiyanovskii ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Orientational Order ◽  
Topological Defects ◽  
Density Fluctuations ◽  
Dermal Fibroblasts ◽  
Produce Cell ◽  
Surface Anchoring ◽  
Liquid Crystal Elastomer ◽  
Anisotropic Surface ◽  
Living Tissues

Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium. The patterns inscribed into the LCE are replicated by the tissue monolayer and cause a strong spatial variation of cells phenotype, their surface density, and number density fluctuations. Unbinding dynamics of defect pairs intrinsic to active matter is suppressed by anisotropic surface anchoring allowing the estimation of the elastic characteristics of the tissues. The demonstrated patterned LCE approach has potential to control the collective behavior of cells in living tissues, cell differentiation, and tissue morphogenesis.

scholarly journals A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Calderón-Alcaraz ◽  
J. Munguía-Valadez ◽  
S. I. Hernández ◽  
A. Ramírez-Hernández ◽  
E. J. Sambriski ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Topological Defects ◽  
Md Simulations ◽  
Structural Behavior ◽  
Nematic Order ◽  
Lower Temperature ◽  
Geometry Characteristic ◽  
Strong Confinement

A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.

scholarly journals Prolate and oblate chiral liquid crystal spheroids

2020 ◽  
Vol 6 (28) ◽  
pp. eaba6728
Author(s):  
Monirosadat Sadati ◽  
Jose A. Martinez-Gonzalez ◽  
Ye Zhou ◽  
Nader Taheri Qazvini ◽  
Khia Kurtenbach ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystalline ◽  
Wearable Sensors ◽  
Mechanical Strain ◽  
Orientational Order ◽  
Topological Defects ◽  
Smart Fabrics ◽  
Chiral Liquid Crystal ◽  
Smart Coatings ◽  
Optical Appearance

Liquid crystals are known to exhibit intriguing textures and color patterns, with applications in display and optical technologies. This work focuses on chiral materials and examines the palette of morphologies that arises when microdroplets are deformed into nonspherical shapes in a controllable manner. Specifically, geometrical confinement and mechanical strain are used to manipulate orientational order, phase transitions, and topological defects that arise in chiral liquid crystal droplets. Inspired by processes encountered in nature, where insects and animals often rely on strain and temperature to alter the optical appearance of dispersed liquid crystalline elements, chiral droplets are dispersed in polymer films and deformation induced by uniaxial or biaxial stretching. Our measurements are interpreted by resorting to simulations of the corresponding systems, thereby providing an in-depth understanding of the morphologies that arise in these materials. The reported structures and assemblies offer potential for applications in smart coatings, smart fabrics, and wearable sensors.

scholarly journals Reconfigurable flows and defect landscape of confined active nematics

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Jérôme Hardoüin ◽  
Rian Hughes ◽  
Amin Doostmohammadi ◽  
Justine Laurent ◽  
Teresa Lopez-Leon ◽  
...  
Keyword(s):  
Average Distance ◽  
Orientational Order ◽  
Topological Defects ◽  
Length Scale ◽  
Chaotic Flows ◽  
Narrow Channels ◽  
Active Length ◽  
Vortex Lattices ◽  
Active Liquid ◽  
Active Flow

Abstract The physics of active liquid crystals is mostly governed by the interplay between elastic forces that align their constituents, and active stresses that destabilize the order with constant nucleation of topological defects and chaotic flows. The average distance between defects, also called active length scale, depends on the competition between these forces. Here, in experiments with the microtubule/kinesin active nematic system, we show that the intrinsic active length scale loses its relevance under strong lateral confinement. Transitions are observed from chaotic to vortex lattices and defect-free unidirectional flows. Defects, which determine the active flow behaviour, are created and annihilated on the channel walls rather than in the bulk, and acquire a strong orientational order in narrow channels. Their nucleation is governed by an instability whose wavelength is effectively screened by the channel width. These results are recovered in simulations, and the comparison highlights the role of boundary conditions.

scholarly journals Curvature Potential Unveiled Topological Defect Attractors

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 539
Author(s):  
Luka Mesarec ◽  
Aleš Iglič ◽  
Veronika Kralj-Iglič ◽  
Wojciech Góźdź ◽  
Epifanio G. Virga ◽  
...  
Keyword(s):  
Parallel Transport ◽  
Orientational Order ◽  
Total Curvature ◽  
Topological Defects ◽  
Axially Symmetric ◽  
Liquid Crystal Films ◽  
Tensor Order ◽  
Crystal Films ◽  
Parameter Field ◽  
Spherical Topology

We consider the theoretical and positional assembling of topological defects (TDs) in effectively two-dimensional nematic liquid crystal films. We use a phenomenological Helfrich–Landau–de Gennes-type mesoscopic model in which geometric shapes and nematic orientational order are expressed in terms of a curvature tensor field and a nematic tensor order parameter field. Extrinsic, intrinsic, and total curvature potentials are introduced using the parallel transport concept. These potentials reveal curvature seeded TD attractors. To test ground configurations, we used axially symmetric nematic films exhibiting spherical topology.

scholarly journals Social wasps repair emergent topological defects

2021 ◽  
Author(s):  
Shivani Krishna ◽  
Apoorva Gopinath ◽  
Somendra M. Bhattacharjee
Keyword(s):  
Short Range ◽  
Amorphous Materials ◽  
Social Insect ◽  
Pair Correlation ◽  
Orientational Order ◽  
Topological Defects ◽  
Social Wasps ◽  
Paper Wasp ◽  
Wasp Species

Social insects have evolved a variety of architectural formations. Bees and wasps are well known for their ability to achieve compact structures by building hexagonal cells. Polistes wattii, an open nesting paper wasp species, builds planar hexagonal structures. Here, using the pair correlation function approach, we show that their nests exhibit short-range hexagonal order but no long-range order akin to amorphous materials. Hexagonal orientational order was well preserved globally. We also show the presence of emergent topological defects such as disclination pairs (pentagon-heptagon dipoles), Stone-Wales quadrupoles, and other higher-order defects and discuss how these defects were fixed in the nest, thereby restoring order. Furthermore, we suggest the possible role of such defects in shaping nesting architectures of other social insect species.

scholarly journals Mosaics of topological defects in micropatterned liquid crystal textures

2018 ◽  
Vol 4 (11) ◽  
pp. eaau8064 ◽  
Author(s):  
Dae Seok Kim ◽  
Simon Čopar ◽  
Uroš Tkalec ◽  
Dong Ki Yoon
Keyword(s):  
Liquid Crystal ◽  
Orientational Order ◽  
Topological Defects ◽  
Smectic Phase ◽  
Dimensional System ◽  
Two Dimensional ◽  
Layer Spacing ◽  
Smectic A ◽  
Lattice Symmetry ◽  
Two Dimensional System

Topological defects in the orientational order that appear in thin slabs of a nematic liquid crystal, as seen in the standard schlieren texture, behave as a random quasi–two-dimensional system with strong optical birefringence. We present an approach to creating and controlling the defects using air pillars, trapped by micropatterned holes in the silicon substrate. The defects are stabilized and positioned by the arrayed air pillars into regular two-dimensional lattices. We explore the effects of hole shape, lattice symmetry, and surface treatment on the resulting lattices of defects and explain their arrangements by application of topological rules. Last, we show the formation of detailed kaleidoscopic textures after the system is cooled down across the nematic–smectic A phase transition, frustrating the defects and surrounding structures with the equal-layer spacing condition of the smectic phase.

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