Measurement of elastic constants of nematic liquid crystals with use of hybrid in-plane-switched cell

2012 ◽  
Vol 20 (3) ◽  
Author(s):  
E. Nowinowski-Kruszelnicki ◽  
J. Kędzierski ◽  
Z. Raszewski ◽  
L. Jaroszewicz ◽  
M. Kojdecki ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Magnetic Fields ◽  
Electric Field ◽  
Elastic Constants ◽  
Nematic Liquid Crystals ◽  
Experimental Tests ◽  
New Method ◽  
Dielectric Anisotropy ◽  
Main Concept

AbstractA new method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is experimentally verified. The main concept relies on exploiting only the electric field and determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in only one hybrid in-plane-switched cell. In such cell the deformations of an investigated liquid crystal are controlled by three separated pairs of electrodes confining measurement domains. In two of them inter-digital electrodes are mounted on one cell cover. Splay, twist and bend elastic constants can be measured by a proper choice of electrodes’ configuration together with orienting cover coatings (without applying magnetic fields). In this paper, we describe layout of our cells and results of experimental tests by using different liquid crystals: 5CB and 6CHBT (with positive dielectric anisotropy), Demus’ esters (with negative dielectric anisotropy) and new liquid crystals mixtures produced in our university.

scholarly journals Electrically Controlled Diffraction Grating in Azo Dye-Doped Liquid Crystals

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 1051 ◽  
Author(s):  
Chuen-Lin Tien ◽  
Rong-Ji Lin ◽  
Chi-Chung Kang ◽  
Bing-Yau Huang ◽  
Chie-Tong Kuo ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Fields ◽  
Azo Dye ◽  
Nematic Liquid Crystals ◽  
Polarized Light ◽  
Dielectric Anisotropy ◽  
Linear Effect ◽  
Periodic Distribution ◽  
The Difference

This research applies the non-linear effect of azo dye-doped liquid crystal materials to develop a small, simple, and adjustable beam-splitting component with grating-like electrodes. Due to the dielectric anisotropy and optical birefringence of nematic liquid crystals, the director of the liquid crystal molecules can be reoriented by applying external electric fields, causing a periodic distribution of refractive indices and resulting in a diffraction phenomenon when a linearly polarized light is introduced. The study also discusses the difference in the refractive index (Δn), the concentration of azo dye, and the rising constant depending on the diffraction signals. The experimental results show that first-order diffraction efficiency can reach ~18% with 0.5 wt % azo dye (DR-1) doped in the nematic liquid crystals.

scholarly journals Holographic Characteristics of Photopolymers Containing Different Mixtures of Nematic Liquid Crystals

Polymers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 325 ◽  
Author(s):  
Sandra Fenoll ◽  
Francisco Brocal ◽  
José David Segura ◽  
Manuel Ortuño ◽  
Augusto Beléndez ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Light Intensity ◽  
Electric Field ◽  
Diffraction Efficiency ◽  
Applied Voltage ◽  
Nematic Liquid Crystals ◽  
Variable Electric Field ◽  
Polymer Dispersed Liquid Crystal ◽  
Polymer Dispersed

A holographic polymer dispersed liquid crystal (HPDLC) is used to record holographic diffraction gratings. Several mixtures of nematic liquid crystals (LC) are used as components of the HPDLC to evaluate their influence in static and dynamic basic properties. The diffraction efficiency obtained in the reconstruction of the holograms is evaluated to compare the influence of the different LC. Additionally, the samples are exposed to a variable electric field and the diffracted light intensity as a function of the applied voltage is measured to evaluate the influence of the LC. The results obtained show significant differences depending on the LC incorporated to the photopolymer.

scholarly journals Field-driven pattern formation in nematic liquid crystals: mesoscopic simulations of electroconvection

RSC Advances ◽  
2017 ◽  
Vol 7 (67) ◽  
pp. 42218-42224 ◽  
Author(s):  
Kuang-Wu Lee ◽  
Thorsten Pöschel
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Pattern Formation ◽  
Electric Field ◽  
External Electric Field ◽  
Nematic Liquid Crystals ◽  
Directional Flow ◽  
Mesoscopic Simulations

Directional flow, which has the potential for precise colloidal transportation, is found in liquid crystal microfluidics under an external electric field.

scholarly journals Variable pitch hydrodynamic electro-optic gratings utilising bent liquid crystal dimers

Soft Matter ◽  
2020 ◽  
Vol 16 (46) ◽  
pp. 10439-10453
Author(s):  
R. Morris ◽  
J. C. Jones ◽  
M. Nagaraj
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Elastic Constants ◽  
Nematic Liquid Crystals ◽  
Diffraction Gratings ◽  
Variable Pitch ◽  
Electro Optic

Electrohydrodynamic Instabilities in nematic liquid crystals cause uniform and continuously variable pitch diffraction gratings. Liquid crystal dimers allow greater range of elastic constants, allowing wider angle diffraction to be achieved.

High Precision Method for Determining Twist Elastic Constants of Nematic Liquid Crystals I. Theory

1974 ◽  
Vol 29 (1) ◽  
pp. 125-130 ◽  
Author(s):  
R. Dreher
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Elastic Constant ◽  
Nematic Liquid Crystal ◽  
High Precision ◽  
Elastic Constants ◽  
Nematic Liquid Crystals ◽  
Precision Method ◽  
Transmission Measurements

In a magnetic field a nematic liquid crystal may sustain a variety of twist modes. Their influence upon light propagating trough the liquid crystal can be used to evaluate the twist elastic constant from simple reflection or transmission measurements.

Pattern Formation in Electrohydrodynamic Convection

MRS Bulletin ◽  
1991 ◽  
Vol 16 (1) ◽  
pp. 46-56 ◽  
Author(s):  
Walter Zimmermann
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Pattern Formation ◽  
Electric Field ◽  
Organic Molecules ◽  
Nematic Liquid Crystals ◽  
Liquid Crystal Displays ◽  
Director Field ◽  
Axis Orientation ◽  
Fundamental Research

One hundred years after their discovery, we meet liquid crystals everywhere in our daily life. Their most widely known application is the liquid crystal displays (LCDs) in watches, pocket calculators, or gasoline pumps. Applications aside, liquid crystals show many exciting properties, making them highly interesting for fundamental research. For example, electrohydrodynamic convection (EHC) in nematic liquid crystals, which is studied in cells of a configuration similar to liquid crystal displays, serves with its characteristic properties as a model System for investigating central questions of pattern formation and chaos.Today's liquid crystal displays work on the principle described in 1971 by Martin Schadt and Wolfgang Helfrich (Figure 1). In nematic liquid crystals, organic molecules orient on average along a macroscopic direction, described by the director field n(r), that has neither head nor tail (n = −n). Nematics are therefore anisotropic and for energetic reasons, n(r) orients parallel (perpendicular) to an electric field when the dielectric permittivity (ε∥) along n is larger (smaller) than the perpendicular (ε⊦ one. For positive εa = ε∥ − ε⊦, when an electric field is applied perpendicular to the direction of n, a reorientation of n takes place together with a corresponding change in the optical property of the cell. The controlled change by an electric field in the optic axis (orientation) in well-defined areas of the display then allows the representation of numbers, etc.

Chemically induced twist-bend nematic liquid crystals, liquid crystal dimers, and negative elastic constants

2013 ◽  
Vol 88 (2) ◽  
Author(s):  
K. Adlem ◽  
M. Čopič ◽  
G. R. Luckhurst ◽  
A. Mertelj ◽  
O. Parri ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Elastic Constants ◽  
Nematic Liquid Crystals ◽  
Chemically Induced

scholarly journals In situ laser-imprinted surface realignment of a nematic liquid crystal

Soft Matter ◽  
2015 ◽  
Vol 11 (17) ◽  
pp. 3347-3353 ◽  
Author(s):  
Giorgio Mirri ◽  
Miha Škarabot ◽  
Igor Muševič
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystal ◽  
Nematic Liquid Crystals ◽  
New Method

We present a new method for the in-plane realignment of nematic liquid crystals in already fully assembled cells with uni-directionally rubbed polyimide as an aligning layer. This method can be applied to obtain twisted and planar μm-sized domains.

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