Switching and induced flow effects in chiral smectic C liquid crystals

1997 ◽  
Vol 8 (3) ◽  
pp. 263-270 ◽  
Author(s):  
GEORGE I. BLAKE ◽  
FRANK M. LESLIE ◽  
MIKE J. TOWLER
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Field ◽  
Boundary Conditions ◽  
Continuum Theory ◽  
Parallel Plates ◽  
Smectic C ◽  
Induced Flow ◽  
Flow Effects

We consider a chiral smectic C liquid crystal confined between parallel plates in the bookshelf geometry. Using a recently proposed continuum theory for such materials the behaviour of the cell is discussed when an electric field is applied and subsequently removed from the cell. We examine both symmetric and asymmetric boundary conditions for the director.

Numerical Study on Liquid Crystalline Actuators Using Back-Flow Effect

2011 ◽  
Vol 211-212 ◽  
pp. 430-433
Author(s):  
Chun Bo Liu ◽  
Long Wang Yue ◽  
Xiao Xia Liu
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Liquid Crystalline ◽  
Numerical Study ◽  
Twist Angle ◽  
Parallel Plates ◽  
Plane Component ◽  
Out Of Plane ◽  
Induced Flow ◽  
Micro Actuators

As a purpose of developing micro-actuators driven by liquid crystals, transient behaviors of a nematic liquid crystal between two parallel plates under an electric field have investigated numerically by using the Leslie-Ericksen theory. Twist angle has been selected as computational parameters. Imposition of an electric field on a liquid crystal induces backflow whose profile and magnitude depend strongly on the twist angle of the director. When the twist angle is 0 degree, the induced flow is planar, and with increasing of the twist angle, the flow has an out of plane component, and finally the profile becomes unidirectional when the twist angle reaches 180 degrees.

Deformation of nematic liquid crystals in an electric field

2002 ◽  
Vol 13 (1) ◽  
pp. 1-23 ◽  
Author(s):  
R. H. SELF ◽  
C. P. PLEASE ◽  
T. J. SLUCKIN
Keyword(s):  
Electromagnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Field ◽  
Asymptotic Methods ◽  
Continuum Theory ◽  
Elastic Stiffness ◽  
Critical Voltage ◽  
Materials Used ◽  
Electrical Permittivity

The behaviour of liquid crystal materials used in display devices is discussed. The underlying continuum theory developed by Frank, Ericksen and Leslie for describing this behaviour is reviewed. Particular attention is paid to the approximations and extensions relevant to existing device technology areas where mathematical analysis would aid device development. To illustrate some of the special behaviour of liquid crystals and in order to demonstrate the techniques employed, the specific case of a nematic liquid crystal held between two parallel electrical conductors is considered. It has long been known that there is a critical voltage below which the internal elastic strength of the liquid crystal exceeds the electric forces and hence the system remains undeformed from its base state. This bifurcation behaviour is called the Freedericksz transition. Conventional analytic analysis of this problem normally considers a magnetic, rather than electric, field or a near-transition voltage since in these cases the electromagnetic field structure decouples from the rest of the problem. Here we consider more practical situations where the electromagnetic field interacts with the liquid crystal deformation. Assuming strong anchoring at surfaces and a one dimensional deformation, three nondimensional parameters are identified. These relate to the applied voltage, the anisotropy of the electrical permittivity of the liquid crystal, and to the anisotropy of the elastic stiffness of the liquid crystal. The analysis uses asymptotic methods to determine the solution in a numerous of different regimes defined by physically relevant limiting cases of the parameters. In particular, results are presented showing the delicate balance between an anisotropic material trying to push the electric field away from regions of large deformation and the deformation trying to be maximum in regions of high electric field.

Surface Forces of the Electric Field Induced Flowin Nematic Liquid Crystals

1984 ◽  
Vol 39 (4) ◽  
pp. 309-319
Author(s):  
J. Grupp
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Field ◽  
Elastic Constant ◽  
Surface Forces ◽  
Time Constants ◽  
Liquid Crystal Films ◽  
Viscosity Term ◽  
Crystal Films ◽  
Induced Flow

In thin nematic liquid crystal films with homeotropic boundaries, surface forces are measured that are produced by an electric field induced flow. The sample is placed between two horizontal circular glass disks in a torsion viscosimeter, where a torque is exerted on the upper disk by these surface forces. The evolution of the induced flow is registered via this torque. The time constants of this evolution, the viscosity term γ1 - α22/ηc and the elastic constant K3 are determined.

Electric-Field-Dependent Tilt (Cone) Angle in a Chiral Smectic C Liquid Crystal Showing Electroclinic Effect in the Smectic A Phase

1991 ◽  
Vol 30 (Part 2, No. 4A) ◽  
pp. L612-L615 ◽  
Author(s):  
Ying-Bao Yang ◽  
Akihiro Mochizuki ◽  
Naoto Nakamura ◽  
Shunsuke Kobayashi
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Cone Angle ◽  
Smectic A ◽  
Smectic C ◽  
Field Dependent ◽  
Smectic A Phase

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.

Nano-Sized Fine Droplets of Liquid Crystals for Optical Application

1996 ◽  
Vol 457 ◽  
Author(s):  
Shiro Matsumoto ◽  
Marthe Houlbert ◽  
Takayoshi Hayashi ◽  
Ken-ichi Kubodera
Keyword(s):  
Liquid Crystal ◽  
Phase Separation ◽  
Liquid Crystals ◽  
Electric Field ◽  
Applied Voltage ◽  
Applied Electric Field ◽  
Uv Curing ◽  
Infrared Region ◽  
High Transparency ◽  
Power Change

ABSTRACTNano-sized fine droplets of liquid crystal (LC) were obtained by phase separation of nematic LC in UV curing polymer. The polymer composite had a high transparency in the infrared region. The fine droplets responded to an electric field causing a change in birefringence. Output power change was brought about by the generated retardation between two polarizations, parallel and perpendicular to the applied electric field. This differs from the composite containing much larger droplets, where output depends on the degree of scattering. The birefringence changed by 0.001 at the applied voltage of 7.5 V/μm.

Bistable nematic liquid crystal device with flexoelectric switching

2006 ◽  
Vol 17 (4) ◽  
pp. 435-463 ◽  
Author(s):  
L. J. CUMMINGS ◽  
G. RICHARDSON
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Nematic Liquid Crystal ◽  
Liquid Crystal Display ◽  
Parallel Plates ◽  
Stable States ◽  
Numerical Work ◽  
Potential Applications ◽  
Simplifying Assumptions ◽  
Bistable Device

Motivated generally by potential applications in the liquid crystal display industry [8,35], and specifically by recent experimental, theoretical and numerical work [6,7,13,14,21,25,30,31], we consider a thin film of nematic liquid crystal (NLC), sandwiched between two parallel plates. Under certain simplifying assumptions, laid out in £2, we find that for monostable surfaces (i.e. only a single preferred director anchoring angle at each surface), two optically-distinct, steady, stable (equal energy) configurations of the director are achievable, that is, a bistable device. Moreover, it is found that the stability of both of these steady states may be destroyed by the application of a sufficiently large electric field, and that switching between the two states is possible, via the flexoelectric effect. Such a phenomenon could be used in NLC display devices, to reduce power consumption drastically. Previous theoretical demonstrations of such (switchable) bistable devices have either relied on having bistable bounding surfaces, that is, surfaces at which there are two preferred director orientations at the surface [7,14]; on having special (nonplanar) surface morphology within the cell that allows for two stable states (the zenithal bistable device (ZBD) [4,21], or, in the case of the Nemoptic BiNem technology [11,19], on flow effects and a very carefully applied electric field to effect the switching.

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.

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