scholarly journals Stable and Metastable Patterns in Chromonic Nematic Liquid Crystal Droplets Forced with Static and Dynamic Magnetic Fields

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 138 ◽  
Author(s):  
Jordi Ignés-Mullol ◽  
Marc Mora ◽  
Berta Martínez-Prat ◽  
Ignasi Vélez-Cerón ◽  
R. Santiago Herrera ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Boundary Conditions ◽  
Isotropic Phase ◽  
Director Field ◽  
Line Defects ◽  
The One ◽  
Bulk Structures ◽  
Microscopy Images

Spherical confinement of nematic liquid crystals leads to the formation of equilibrium director field configurations that include point and line defects. Driving these materials with flows or dynamic fields often results in the formation of alternative metastable states. In this article, we study the effect of magnetic field alignment, both under static and dynamic conditions, of nematic gems (nematic droplets in coexistence with the isotropic phase) and emulsified nematic droplets of a lyotropic chromonic liquid crystal. We use a custom polarizing optical microscopy assembly that incorporates a permanent magnet whose strength and orientation can be dynamically changed. By comparing simulated optical patterns with microscopy images, we measure an equilibrium twisted bipolar pattern within nematic gems that is only marginally different from the one reported for emulsified droplets. Both systems evolve to concentric configurations upon application of a static magnetic field, but behave very differently when the field is rotated. While the concentric texture within the emulsified droplets is preserved and only displays asynchronous oscillations for high rotating speeds, the nematic gems transform into a metastable untwisted bipolar configuration that is memorized by the system when the field is removed. Our results demonstrate the importance of boundary conditions in determining the dynamic behavior of confined liquid crystals even for configurations that share similar equilibrium bulk structures.

On the Field-Induced Cholesteric-Nematic Transition in Cholesteric Liquid Crystals with Homeotropic Boundary Conditions

1983 ◽  
Vol 38 (1) ◽  
pp. 1-9 ◽  
Author(s):  
J. Brokx ◽  
G. Vertogen ◽  
E. W. C. van Groesen
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
Boundary Conditions ◽  
Difference Method ◽  
Lagrange Equation ◽  
Helix Axis ◽  
Cholesteric Liquid Crystals ◽  
Director Field ◽  
Fréedericksz Transition ◽  
The Difference

Abstract The influence of homeotropic boundary conditions on the cholesteric-nematic transition is discussed, starting from the assumption that the director field consists of only components perpendicular to the helix axis, which is directed parallel to the boundary planes. Attention is paid to the solution of Cladis and Kléman for the simpler case without magnetic field. Their solution, consisting of regularly spaced line signularities, is derived in another more transparent way. Besides it is shown that even director fields without singularities are possible. The presence of a magnetic field complicates the solution considerably. Now the relevant Euler-Lagrange equation is solved in an approximate way by partly resorting to the difference method. The usefulness of the method is demonstrated by applying this technique to the nematic-cholesteric transition and the Fréedericksz transition in nematics.

Liquid crystal alignment in cylindrical microcapillaries

2012 ◽  
Vol 20 (1) ◽  
Author(s):  
M. Chychłowski ◽  
O. Yaroshchuk ◽  
R. Kravchuk ◽  
T. Woliński
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Photonic Crystal ◽  
Boundary Conditions ◽  
Photonic Crystal Fibers ◽  
Optical Devices ◽  
Liquid Crystal Alignment ◽  
Disclination Line ◽  
Crystal Alignment ◽  
Crystal Fibers

AbstractA variety of alignment configurations of liquid crystals (LCs) inside the glassy cylindrical capillaries is realized by using alignment materials providing different anchoring. The radial configuration with central disclination line is obtained for homeotropic boundary conditions. In turn, the axial, transversal and tilted alignment structures are realized by using materials for planar anchoring. The uniformity and controlling of the latter structures were provided by photoalignment method. This approach can be further used to control LC alignment in the photonic crystal fibers recognized as advanced elements for different optical devices.

Liquid crystal/glass interface effects on the orientation of lyotropic liquid crystals in magnetic fields

1978 ◽  
Vol 56 (16) ◽  
pp. 2178-2183 ◽  
Author(s):  
Fred Y. Fujiwara ◽  
Leonard W. Reeves
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Cylindrical Tube ◽  
Lyotropic Liquid Crystals ◽  
Crystal Glass ◽  
Type I ◽  
Type Ii ◽  
Glass Interface ◽  
Interface Effects

Lyotropic mesophases of both positive (type I) and negative (type II) diamagnetic anisotropy have been prepared. The deuterium magnetic resonance signal from D2O in the sample bas been studied during the process of orientation in a magnetic field. A type II mesophase oriented by a magnetic field in a cylindrical tube perpendicular to the lines of force does not achieve a uniform distribution of directors in a plane perpendicular to the field. The re orientation of a type I mesophase after an initial displacement of the director at an angle to the field has been studied. Previous equations derived for thermotropic liquid crystals are applicable but the velocity of re-orientation was found to be an inverse function of the radius, for nmr tubes of less than 4 mm in diameter, indicating that liquid crystal/glass interface effects are important.

An in-plane switching liquid crystal cell with weakly anchored liquid crystals on the electrode substrate

2017 ◽  
Vol 5 (18) ◽  
pp. 4384-4387 ◽  
Author(s):  
O. Sato ◽  
N. Iwata ◽  
J. Kawamura ◽  
T. Maeda ◽  
Y. Tsujii ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Liquid Crystal Displays ◽  
Polyimide Film ◽  
Liquid Crystal Cell ◽  
Crystal Cell ◽  
Hexyl Methacrylate ◽  
The One

We present the “one-side zero-anchoring in-plane switching” (OZ-IPS) mode in liquid crystal displays (LCDs) comprising an electrode substrate onto which poly(hexyl methacrylate) chains are grafted and a counter substrate coated with a rubbed polyimide film.

scholarly journals Dynamic behavior of a nematic liquid crystal mixed with CoFe2O4 ferromagnetic nanoparticles in a magnetic field

2017 ◽  
Vol 8 ◽  
pp. 2467-2473 ◽  
Author(s):  
Emil Petrescu ◽  
Cristina Cirtoaje ◽  
Cristina Stan
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Dynamic Behavior ◽  
Small Deviation ◽  
Large Size ◽  
Polarized Microscopy ◽  
Nematic Director ◽  
Small Distortion ◽  
The Magnetic Field ◽  
Microscopy Images

The dynamic behavior of a mixture of 4-cyano-4′-pentylbiphenyl (5CB) with 1% CoFe2O4 nanoparticles was analyzed. Experimental data indicate a high stability of the nematic director in the mixture compared to a reference 5CB sample in the magnetic field. The ferrite nanoparticles agglomerate forming long chains as observed in polarized microscopy images. These chains have a very high influence on the magneto-optic effect of the cell. When the magnetic field is applied on the mixture, the chains tend to align with the field direction but, due to their large size, they remain oriented obliquely between the support plates. Thus, the nematic molecules anchored on their surface can not reorient with the field and only a small distortion angle of the liquid crystal molecular director is observed. A comparison with a previously developed theoretical model confirms this small deviation.

scholarly journals Bifurcation analysis of the twist-Fréedericksz transition in a nematic liquid-crystal cell with pre-twist boundary conditions

2009 ◽  
Vol 20 (3) ◽  
pp. 269-287 ◽  
Author(s):  
FERNANDO P. DA COSTA ◽  
EUGENE C. GARTLAND ◽  
MICHAEL GRINFELD ◽  
JOÃO T. PINTO
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Boundary Conditions ◽  
Nematic Liquid Crystal ◽  
Pitchfork Bifurcation ◽  
Critical Magnetic Field ◽  
Twist Boundary ◽  
Freedericksz Transition ◽  
Diamagnetic Anisotropy ◽  
Fréedericksz Transition

Motivated by a recent investigation of Millar and McKay [Director orientation of a twisted nematic under the influence of an in-plane magnetic field. Mol. Cryst. Liq. Cryst435, 277/[937]–286/[946] (2005)], we study the magnetic field twist-Fréedericksz transition for a nematic liquid crystal of positive diamagnetic anisotropy with strong anchoring and pre-twist boundary conditions. Despite the pre-twist, the system still possesses ℤ2 symmetry and a symmetry-breaking pitchfork bifurcation, which occurs at a critical magnetic-field strength that, as we prove, is above the threshold for the classical twist-Fréedericksz transition (which has no pre-twist). It was observed numerically by Millar and McKay that this instability occurs precisely at the point at which the ground-state solution loses its monotonicity (with respect to the position coordinate across the cell gap). We explain this surprising observation using a rigorous phase-space analysis.

scholarly journals Interactions on the Interface between Two Liquid Crystal Materials

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 393 ◽  
Author(s):  
Rok Geršak ◽  
Simon Čopar
Keyword(s):  
Numerical Simulation ◽  
Liquid Crystal ◽  
Boundary Conditions ◽  
Chemical Treatment ◽  
Molecular Orientation ◽  
Glass Plate ◽  
External Fields ◽  
Intrinsic Properties ◽  
Director Field ◽  
Surface Alignment

In liquid crystal applications, boundary conditions are essential to ensuring suitable bulk molecular orientation and a deterministic response to external fields. Be it confinement to a droplet or a shell, a glass plate, or an interface with air or another liquid, proper surface alignment must be ensured—mechanically by rubbing, by chemical treatment that adds a layer of aligning molecules, by using photoalignment or even by leaving the surface untreated, using the intrinsic properties of the substrate itself. The anchoring can be classified as unidirectional (perpendicular homeotropic, or at oblique angles), or degenerate (planar or pre-tilted). However, if both substances at the interface are anisotropic, more diverse behaviour is expected. Here, we present a numerical simulation of a nematic droplet in a nematic host, and investigate behaviour of the director field and defects at the interface for different interfacial couplings. Finally, we compare the simulations to experimental images of discotic droplets in a calamitic nematic host.

Investigation of the Finite Size Properties of the Ising Model Under Various Boundary Conditions

2020 ◽  
Vol 75 (2) ◽  
pp. 175-182
Author(s):  
Magdy E. Amin ◽  
Mohamed Moubark ◽  
Yasmin Amin
Keyword(s):  
Magnetic Field ◽  
Ising Model ◽  
Boundary Conditions ◽  
Finite Size ◽  
Scaling Functions ◽  
Finite Size Scaling ◽  
One Dimensional ◽  
Various Boundary Conditions ◽  
The One ◽  
Bulk Case

AbstractThe one-dimensional Ising model with various boundary conditions is considered. Exact expressions for the thermodynamic and magnetic properties of the model using different kinds of boundary conditions [Dirichlet (D), Neumann (N), and a combination of Neumann–Dirichlet (ND)] are presented in the absence (presence) of a magnetic field. The finite-size scaling functions for internal energy, heat capacity, entropy, magnetisation, and magnetic susceptibility are derived and analysed as function of the temperature and the field. We show that the properties of the one-dimensional Ising model is affected by the finite size of the system and the imposed boundary conditions. The thermodynamic limit in which the finite-size functions approach the bulk case is also discussed.

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