Nontrivial topological defects of micro-rods immersed in nematics and their phototuning

2022 ◽  
Author(s):  
Satoshi Aya ◽  
Junichi Kogo ◽  
Fumito Araoka ◽  
Osamu Haba ◽  
Koichiro Yonetake
Keyword(s):  
Topological Defects ◽  
Single System ◽  
Surface Anchoring ◽  
Topological Structures ◽  
Colloid Systems

Combinations of different geometry and the surface anchoring conditions give rise to the diversity of topological structures in nematic colloid systems. Tuning these parameters in a single system offers possibilities...

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.

Liquid Crystals

2015 ◽  
Author(s):  
Oleg D. Lavrentovich
Keyword(s):  
Molecular Weight ◽  
Thermal Expansion ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Soft Matter ◽  
Topological Defects ◽  
Low Molecular Weight ◽  
Surface Anchoring ◽  
Director Dynamics ◽  
Anisotropic Viscosity

This article discusses modern directions of research in liquid crystals (LCs). LCs represent one of the best studied classes of soft matter, along with colloids, polymer solutions and melts, gels, and foams. Phenomena observed in LCs and approaches developed for their description become of heuristic value in other branches of science. This article considers the basic properties of low-molecular weight thermotropic LCs, with an additional emphasis on the developments of the last decade, such as LC colloids. It begins with an overview of thermotropic and lyotropic systems, followed by a review of the concept of order parameter, elasticity, surface anchoring, and topological defects. It also evaluates hybrid systems combining LCs with polymers or colloids, along with new ways of creating mesomorphic systems and the dynamics of LCs, including anisotropic viscosity, director dynamics and the Frederiks transition, and flow induced by thermal expansion. Finally, it describes various applications of LCs.

scholarly journals Novel optofluidic concepts enabled by topological microfluidics-INVITED

2021 ◽  
Vol 255 ◽  
pp. 10002
Author(s):  
Anupam Sengupta
Keyword(s):  
Material Properties ◽  
Topological Defects ◽  
Optical Fields ◽  
Surface Anchoring ◽  
Micro Scale ◽  
Mechanical Responses ◽  
Non Invasive ◽  
The Rich ◽  
Director Orientation

The coupling between flow and director orientation of liquid crystals (LCs) has been long utilized to devise wide-ranging applications spanning modern displays, medical and environmental solutions, and bio-inspired designs and applications. LC-based optofluidic platforms offer a non-invasive handle to modulate light and material fields, both locally and dynamically. The flow-driven reorientation of the LC molecules can tailor distinct optical and mechanical responses in microfluidic confinements, and harness the coupling therein. Yet the synergy between traditional optofluidics with isotropic fluids and LC microfluidics remains at its infancy. Here, we discuss emerging optofluidic concepts based on Topological Microfluidics, leveraging microfluidic control of topological defects and defect landscapes. With a specific focus on the role of surface anchoring and microfluidic geometry, we present recent and ongoing works that harness flow-controlled director and defect configurations to modulate optical fields. The flow-induced optical attributes, and the corresponding feedback, is enhanced in the vicinity of the topological defects which geenerate distinct isotropic opto-material properties within an anisotropic matrix. By harnessing the rich interplay of confining geometry, anchoring and micro-scale nematodynamics, topological microfluidics offers a promising platform to ideate the next generation of optofluidic and optomechnical concepts.

scholarly journals Surface anchoring controls orientation of a microswimmer in nematic liquid crystal

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Hai Chi ◽  
Mykhailo Potomkin ◽  
Lei Zhang ◽  
Leonid Berlyand ◽  
Igor S. Aranson
Keyword(s):  
Liquid Crystal ◽  
Critical Case ◽  
Topological Defects ◽  
Water Soluble ◽  
Critical Surface ◽  
Bacteria Transport ◽  
Surface Anchoring ◽  
Swimming Direction ◽  
Anchoring Strength ◽  
Surface Anchoring Strength

Abstract Microscopic swimmers, both living and synthetic, often dwell in anisotropic viscoelastic environments. The most representative realization of such an environment is water-soluble liquid crystals. Here, we study how the local orientation order of liquid crystal affects the motion of a prototypical elliptical microswimmer. In the framework of well-validated Beris-Edwards model, we show that the microswimmer’s shape and its surface anchoring strength affect the swimming direction and can lead to reorientation transition. Furthermore, there exists a critical surface anchoring strength for non-spherical bacteria-like microswimmers, such that swimming occurs perpendicular in a sub-critical case and parallel in super-critical case. Finally, we demonstrate that for large propulsion speeds active microswimmers generate topological defects in the bulk of the liquid crystal. We show that the location of these defects elucidates how a microswimmer chooses its swimming direction. Our results can guide experimental works on control of bacteria transport in complex anisotropic environments.

scholarly journals Annihilation of Highly-Charged Topological Defects

Crystals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 673
Author(s):  
Eva Klemenčič ◽  
Pavlo Kurioz ◽  
Milan Ambrožič ◽  
Charles Rosenblatt ◽  
Samo Kralj
Keyword(s):  
Topological Defects ◽  
Phenomenological Approach ◽  
Experimental Sample ◽  
Surface Anchoring ◽  
Nematic Order ◽  
Atomic Force ◽  
Sharp Edges ◽  
Additional Defect ◽  
Cartesian Coordinate ◽  
External Stimuli

We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.

scholarly journals Topological structures, spontaneous symmetry breaking and energy spectra in dipole hexagonal lattices

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Josep Batle
Keyword(s):  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Minimum Energy ◽  
Three Dimensional ◽  
Topological Defects ◽  
Dipole Interaction ◽  
Honeycomb Lattice ◽  
Two Dimensional ◽  
Topological Structures ◽  
Dipole Force

AbstractThe interplay between the special triangular/hexagonal two dimensional lattice and the long range dipole–dipole interaction gives rise to topological defects, specifically the vortex, formed by a particular arrangement of the interacting classic dipoles. The nature of such vortices has been traditionally explained on the basis of numerical evidence. Here we propose the emerging formation of vortices as the natural minimum energy configuration of interacting (in-plane) two-dimensional dipoles based on the mechanism of spontaneous symmetry breaking. As opposed to the quantal case, where spin textures such as skyrmions or bimerons occur due to non-linearities in their Hamiltonian, it is still possible to witness classic topological structures due only to the nature of the dipole–dipole force. We shall present other (new) topological structures for the in-plane honeycomb lattice, as well as for two-dimensional out-of-plane dipoles. These structures will prove to be essential in the minimum energy configurations for three-dimensional simple hexagonal and hexagonal-closed-packed structures, whose energies in the bulk are obtained for the first time.

scholarly journals The rise of Newtonian drops in a nematic liquid crystal

2007 ◽  
Vol 593 ◽  
pp. 385-404 ◽  
Author(s):  
CHUNFENG ZHOU ◽  
PENGTAO YUE ◽  
JAMES J. FENG
Keyword(s):  
Liquid Crystal ◽  
Flow Field ◽  
Point Defect ◽  
Nematic Liquid Crystal ◽  
Topological Defects ◽  
Diffuse Interface ◽  
Initial Surface ◽  
Surface Anchoring ◽  
Moving Interface ◽  
The Stability

We simulate the rise of Newtonian drops in a nematic liquid crystal parallel to the far-field molecular orientation. The moving interface is computed in a diffuse-interface framework, and the anisotropic rheology of the liquid crystal is represented by the Leslie–Ericksen theory, regularized to permit topological defects. Results reveal interesting coupling between the flow field and the orientational field surrounding the drop, especially the defect configuration. The flow generally sweeps the point and ring defects downstream, and may transform a ring defect into a point defect. The stability of these defects and their transformation are depicted in a phase diagram in terms of the Ericksen number and the ratio between surface anchoring and bulk elastic energies. The nematic orientation affects the flow field in return. Drops with planar anchoring on the surface rise faster than those with homeotropic anchoring, and the former features a vortex ring in the wake. These are attributed to the viscous anisotropy of the nematic. With homeotropic anchoring, the drop rising velocity experiences an overshoot, owing to the transformation of the initial surface ring defect to a satellite point defect. With both types of anchoring, the drag coefficient of the drop decreases with increasing Ericksen number as the flow-alignment of the nematic orientation reduces the effective viscosity of the liquid crystal.

scholarly journals Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 249 ◽  
Author(s):  
Mikhail N. Krakhalev ◽  
Rashid G. Bikbaev ◽  
Vitaly S. Sutormin ◽  
Ivan V. Timofeev ◽  
Victor Ya. Zyryanov
Keyword(s):  
Boundary Conditions ◽  
Energy Minimization ◽  
Periodic Structures ◽  
Cholesteric Liquid Crystal ◽  
Topological Defects ◽  
Director Field ◽  
Surface Anchoring ◽  
Minimization Procedure ◽  
Optical Textures ◽  
Difference Time

Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch.

Langerhans-Zell-Histiozytose (LCH)

2014 ◽  
Vol 14 (04) ◽  
pp. 253-259
Author(s):  
C. Hutter ◽  
L. Ronceray ◽  
K. Lakatos ◽  
M. Minkov ◽  
W. Holter ◽  
...  
Keyword(s):  
Single System

ZusammenfassungDie Langerhans-Zell-Histiozytose (LCH) ist eine seltene histiozytäre Erkrankung (Inzidenz: 0,2–2,0/100 000 Kinder unter 15 Jahren) mit einem sehr heterogenen klinischen Verlauf. Spontane Regressionen werden ebenso beobachtet wie chronische Reaktivierungen. Das klinische Spektrum reicht von einem isolierten Befall des Skeletts oder der Haut, bis hin zur ausgedehnten Multiorganerkrankung mit einem progredienten und lebensbedrohli-chen Verlauf. Das diagnostische und therapeutische Vorgehen konnte durch prospektive internationale Studien der Histiocyte Society standardisiert werden. Dies resultiert in einer Verbesserung von Heilungsrate und Prognose. Je nach Krankheitsausdehnung reicht die Behandlungsstrategie von einer abwartenden Haltung oder dem Einsatz einer lokalen/topischen Therapie bei monosystemischer LCH (single system LCH; SS-LCH) bis hin zur systemischen Chemotherapie bei multi-systemischer LCH (MS-LCH). Auch auf dem Gebiet der Grundlagenforschung konnten in den letzten Jahren große Fortschritte im Hinblick auf ein besseres Verständnis der Biologie und Pathogenese der Erkrankung erzielt werden. Die dabei gewonnenen Informationen werden als Grundlage für neue Therapieansätze dienen.

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