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.

scholarly journals Electrically turning periodic structures in cholesteric layer with conical–planar boundary conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Oxana Prishchepa ◽  
Mikhail Krakhalev ◽  
Vladimir Rudyak ◽  
Vitaly Sutormin ◽  
Victor Zyryanov
Keyword(s):  
Boundary Conditions ◽  
Periodic Structures ◽  
Cholesteric Liquid Crystal ◽  
Growth Direction ◽  
Smooth Transition ◽  
Defect Structures ◽  
Optical Cell ◽  
Elastic Continuum ◽  
The One ◽  
Experimental Findings

AbstractElectro-optical cell based on the cholesteric liquid crystal is studied with unique combination of the boundary conditions: conical anchoring on the one substrate and planar anchoring on another one. Periodic structures in cholesteric layer and their transformation under applied electric field are considered by polarizing optical microscopy, the experimental findings are supported by the data of the calculations performed using the extended Frank elastic continuum approach. Such structures are the set of alternating over- and under-twisted defect lines whose azimuthal director angles differ by $$180^\circ$$ 180 ∘ . The $$U^+$$ U + and $$U^-$$ U - -defects of periodicity, which are the smooth transition between the defect lines, are observed at the edge of electrode area. The growth direction of defect lines forming a diffraction grating can be controlled by applying a voltage in the range of $$0\le \, V \le 1.3$$ 0 ≤ V ≤ 1.3  V during the process. Resulting orientation and distance between the lines don’t change under voltage. However, at $$V>1.3$$ V > 1.3  V $$U^+$$ U + -defects move along the defect lines away from the electrode edges, and, finally, the grating lines collapse at the cell’s center. These results open a way for the use of such cholesteric material in applications with periodic defect structures where a periodicity, orientation, and configuration of defects should be adjusted.

scholarly journals Tuning the defect configurations in nematic and smectic liquid crystalline shells

2013 ◽  
Vol 371 (1988) ◽  
pp. 20120258 ◽  
Author(s):  
Hsin-Ling Liang ◽  
JungHyun Noh ◽  
Rudolf Zentel ◽  
Per Rudquist ◽  
Jan P.F. Lagerwall
Keyword(s):  
Boundary Conditions ◽  
Self Assembly ◽  
Liquid Crystalline ◽  
Topological Defects ◽  
Microfluidic System ◽  
Director Field ◽  
Smectic Phases ◽  
Anchor Points ◽  
External Forces ◽  
Linker Molecules

Thin liquid crystalline shells surrounding and surrounded by aqueous phases can be conveniently produced using a nested capillary microfluidic system, as was first demonstrated by Fernandez-Nieves et al. in 2007. By choosing particular combinations of stabilizers in the internal and external phases, different types of alignment, uniform or hybrid, can be ensured within the shell. Here, we investigate shells in the nematic and smectic phases under varying boundary conditions, focusing in particular on textural transformations during phase transitions, on the interaction between topological defects in the director field and inclusions in the liquid crystal (LC), and on the possibility to relocate defects within the shell by rotating the shell in the gravitational field. We demonstrate that inclusions in a shell can seed defects that cannot form in a pristine shell, adding a further means of tuning the defect configuration, and that shells in which the internal aqueous phase is not density matched with the LC will gently rearrange the internal structure upon a rotation that changes the influence of gravity. Because the defects can act as anchor points for added linker molecules, allowing self-assembly of adjacent shells, the various arrangements of defects developing in these shells and the possibility of tuning the result by modifying boundary conditions, LC phase, thickness and diameter of the shell or applying external forces make this new LC configuration very attractive.

scholarly journals Shaping nanoparticle fingerprints at the interface of cholesteric droplets

2018 ◽  
Vol 4 (10) ◽  
pp. eaat8597 ◽  
Author(s):  
Lisa Tran ◽  
Hye-Na Kim ◽  
Ningwei Li ◽  
Shu Yang ◽  
Kathleen J. Stebe ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Periodic Structures ◽  
Water Solution ◽  
Cholesteric Liquid Crystal ◽  
Solution Ph ◽  
Surrounding Water ◽  
Particle Assembly ◽  
Interfacial Assembly ◽  
Energy Applications ◽  
Geometric Frustration

The ordering of nanoparticles into predetermined configurations is of importance to the design of advanced technologies. Here, we balance the interfacial energy of nanoparticles against the elastic energy of cholesteric liquid crystals to dynamically shape nanoparticle assemblies at a fluid interface. By adjusting the concentration of surfactant that plays the dual role of tuning the degree of nanoparticle hydrophobicity and altering the molecular anchoring of liquid crystals, we pattern nanoparticles at the interface of cholesteric liquid crystal emulsions. In this system, interfacial assembly is tempered by elastic patterns that arise from the geometric frustration of confined cholesterics. Patterns are tunable by varying both surfactant and chiral dopant concentrations. Adjusting the particle hydrophobicity more finely by regulating the surfactant concentration and solution pH further modifies the rigidity of assemblies, giving rise to surprising assembly dynamics dictated by the underlying elasticity of the cholesteric. Because particle assembly occurs at the interface with the desired structures exposed to the surrounding water solution, we demonstrate that particles can be readily cross-linked and manipulated, forming structures that retain their shape under external perturbations. This study serves as a foundation for better understanding inter-nanoparticle interactions at interfaces by tempering their assembly with elasticity and for creating materials with chemical heterogeneity and linear, periodic structures, essential for optical and energy applications.

scholarly journals Особенности релаксации тензора напряжения в микроскопическом объеме нематической фазы под действием сильного электрического поля

2018 ◽  
Vol 60 (2) ◽  
pp. 405
Author(s):  
А.В. Захаров
Keyword(s):  
Dissipation Rate ◽  
Periodic Structures ◽  
Numerical Study ◽  
Strong Electric Field ◽  
Rectangular Channel ◽  
Energy Dissipation Rate ◽  
Director Field ◽  
Rotational Displacement ◽  
Nonlinear Generalization ◽  
Angle Alpha

AbstractA numerical study of new regimes of reorientation of director field n̂ , velocity v , and components of stress tensor σ_ ij ( ij = x , y , z ) of nematic liquid crystal (LC) encapsulated in a rectangular channel under the action of a strong electric field E directed at angle $$\alpha \left( {\sim\frac{\pi } {2}} \right)$$ α ( ∼ π 2 ) to the horizontal surfaces bounding the LC channel is proposed. The numerical calculations performed in the framework of nonlinear generalization of the classical Eriksen-Leslie theory have shown that at certain relations between the torques and momenta affecting the unit LC volume and E ≫ E _th, transition periodic structures can emerge during reorientation of n̂ , if the corresponding distortion mode has the fastest response, and, thus, suppress all other modes. Rotating domains originating within this process decrease the energy dissipation rate and create more favorable regimes of the director field reorientation, as compared with the uniform rotational displacement.

Topological defects in nematic films between planar degenerate surfaces. A Monte Carlo study

2021 ◽  
pp. 2250016
Author(s):  
Cesare Chiccoli ◽  
Paolo Pasini ◽  
Luiz Roberto Evangelista ◽  
Rodolfo Teixeira de Souza ◽  
Claudio Zannoni
Keyword(s):  
Monte Carlo ◽  
Boundary Conditions ◽  
Monte Carlo Simulations ◽  
Defect Structure ◽  
Topological Defects ◽  
Monte Carlo Study ◽  
Geometric Parameters ◽  
Molecular Organization ◽  
The One

The molecular organization of a nematic film sandwiched between two planar randomly aligned surfaces is studied by means of detailed Monte Carlo simulations. The formation as well as the evolution of topological defects induced by these particular boundary conditions are investigated. The resulting defect structure is compared with the one induced by hybrid aligned surfaces. The observation of such defects and some features of their structures can be associated with geometric parameters of the film and with properties of the confining surfaces.

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...

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