scholarly journals Multifrequency Driven Nematics

Crystals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 275 ◽  
Author(s):  
Noureddine Bennis ◽  
Jakub Herman ◽  
Aleksandra Kalbarczyk ◽  
Przemysław Kula ◽  
Leszek R. Jaroszewicz
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Fields ◽  
Dielectric Anisotropy ◽  
Dielectric Measurements ◽  
Frequency Tunability ◽  
Frequency Tunable ◽  
Electrooptical Properties ◽  
Crystal Characterization

Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we present electrooptical properties of novel liquid crystal (LC) mixture with frequency tunable capabilities from 100Hz to 10 KHz at constant applied voltage. The frequency tunability of presented mixtures shown here came from composition of three different families of rodlike liquid crystals. Dielectric measurements are reported for the compounds constituting frequency-controlled birefringence liquid crystal. Characterization protocols allowing the optimum classification of different components of this mixture, paying attention to all relevant parameters such as anisotropic polarizability, dielectric anisotropy, and dipole moment are presented.

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 Photoluminescence of CdSe/ZnS quantum dots in nematic liquid crystals in electric fields

2018 ◽  
Vol 9 ◽  
pp. 1544-1549 ◽  
Author(s):  
Margarita A Kurochkina ◽  
Elena A Konshina ◽  
Daria Khmelevskaia
Keyword(s):  
Quantum Dots ◽  
Liquid Crystals ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Electric Fields ◽  
Dielectric Anisotropy ◽  
Vertical Position ◽  
Decay Times ◽  
Pl Intensity

We have experimentally investigated the effect of the reorientation of a nematic liquid crystal (LC) in an electric field on the photoluminescence (PL) of CdSe/ZnS semiconductor quantum dots (QDs). To the LC with positive dielectric anisotropy, 1 wt % QDs with a core diameter of 5 nm was added. We compared the change of PL intensity and decay times of QDs in LC cells with initially planar or vertically orientated molecules, i.e., in active or passive LC matrices. The PL intensity of the QDs increases four-fold in the active LC matrix and only 1.6-fold in the passive LC matrix without reorientation of the LC molecules. With increasing electric field strength, the quenching of QDs luminescence occurred in the active LC matrix, while the PL intensity did not change in the passive LC matrix. The change in the decay time with increasing electric field strength was similar to the behavior of the PL intensity. The observed buildup in the QDs luminescence can be associated with the transfer of energy from LC molecules to QDs. In a confocal microscope, we observed the increase of particle size and the redistribution of particles in the active LC matrix with the change of the electric field strength. At the same time, no significant changes occurred in the passive LC matrix. With the reorientation of LC molecules from the planar in vertical position in the LC active matrix, quenching of QD luminescence and an increase of the ion current took place simultaneously. The obtained results are interesting for controlling the PL intensity of semiconductor QDs in liquid crystals by the application of electric fields.

scholarly journals Installation for measuring the dielectric anisotropy of liquid crystals at low frequencies by the bridge method with constant displacement

2021 ◽  
Vol 1198 (1) ◽  
pp. 012006
Author(s):  
S V Kalashnikov ◽  
N A Romanov ◽  
A V Nomoev
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Internal Resistance ◽  
Dielectric Anisotropy ◽  
Dielectric Parameters ◽  
Low Frequencies ◽  
Offset Voltage ◽  
Wide Range ◽  
Ac Current ◽  
Constant Displacement

Abstract Installation designed to measure the dielectric anisotropy in laboratory studies of liquid crystal polymer films is described. The installation operates on the principle of a balanced alternating current (AC) bridge, allowing the application of a direct external current (bias) to the liquid crystal cell. The internal resistance of the direct current (DC) source, which affects the equilibrium condition of the bridge, is compensated. The frequency of the AC current feeding the bridge and the offset voltage of the cell is regulated within a wide range, which makes it possible to study various functional dependences of the dielectric parameters of liquid crystals and their modifiers.Introduction

scholarly journals Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

2020 ◽  
Vol 16 ◽  
pp. 674-680 ◽  
Author(s):  
Zeguo Fang ◽  
Nawaf Al-Maharik ◽  
Peer Kirsch ◽  
Matthias Bremer ◽  
Alexandra M Z Slawin ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Thermodynamic Properties ◽  
Organic Liquid ◽  
Dielectric Anisotropy ◽  
Structure Property ◽  
Structure Property Relationships

This paper describes the synthesis of a series of organic liquid crystals (LCs) containing selectively fluorinated cyclopropanes at their termini. The syntheses used difluorocarbene additions to olefin precursors, an approach which proved straightforward such that these liquid crystal candidates could be efficiently prepared. Their physical and thermodynamic properties were evaluated and depending on individual structures, they either displayed positive or negative dielectric anisotropy. The study gives some guidance into effective structure–property relationships for the design of LCs containing selectively fluorinated cyclopropane motifs.

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 Ion-Generating and Ion-Capturing Nanomaterials in Liquid Crystals

Proceedings ◽  
2018 ◽  
Vol 2 (14) ◽  
pp. 1122
Author(s):  
Yuriy Garbovskiy
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Fields ◽  
Future Research ◽  
Research Directions ◽  
Liquid Crystal Devices ◽  
Proposed Model ◽  
Future Research Directions ◽  
Practical Implications ◽  
Good Agreement

The majority of tunable liquid crystal devices are driven by electric fields. The performance of such devices can be altered by the presence of small amounts of ions in liquid crystals. Therefore, the understanding of possible sources of ions in liquid crystal materials is very critical to a broad range of existing and future applications employing liquid crystals. Recently, nanomaterials in liquid crystals have emerged as a hot research topic, promising for its implementation in the design of wearable and tunable liquid crystal devices. An analysis of published results revealed that nanodopants in liquid crystals can act as either ion-capturing agents or ion-generating objects. In this presentation, a recently developed model of contaminated nanomaterials is analyzed. Nanoparticle-enabled ion capturing and ion generation regimes in liquid crystals are discussed within the framework of the proposed model. This model is in very good agreement with existing experimental results. Practical implications and future research directions are also discussed.

A Novel Method for Measuring the Difference in Flexoelectric Coefficients of Nematic Liquid Crystals

2011 ◽  
Vol 181-182 ◽  
pp. 26-32
Author(s):  
Benjamin I. Outram ◽  
Steve J. Elston
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystal ◽  
Electric Fields ◽  
Nematic Liquid Crystals ◽  
Angle Of Incidence ◽  
Rotation Method ◽  
Twisted Nematic ◽  
Novel Method ◽  
The Difference

The difference between e1 and e3 parameters for flexoelectric polarization, as originally defined byMeyer, is measured for nematic liquid crystal materials E7 and BL087 in Twisted Nematic (TN) cells with In-Plane Switching (IPS) electric fields using the crystal rotation method, which measures transmission as a function of angle of incidence. Values of e1 − e3 for E7 and BL087 are found to be 7.2±1.0 pCm−1 and 9.4±1.0 pCm−1 respectively.

scholarly journals Evaluating the Concentration of Ions in Liquid Crystal Cells: Hidden Factors and Useful Techniques

Proceedings ◽  
2021 ◽  
Vol 62 (1) ◽  
pp. 10
Author(s):  
Yuriy Garbovskiy
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Fields ◽  
Measurement Techniques ◽  
Ion Concentration ◽  
Ion Generation ◽  
Concentration Of Ions ◽  
Generation Mechanisms ◽  
Crystal Cells ◽  
Liquid Crystal Materials

Many liquid crystal devices are driven by electric fields. Ions, typically present in molecular liquid crystal materials in minute quantities, can compromise the performance of mesogenic materials (in the simplest case, through a well-known screening effect). Even highly purified liquid crystals can be contaminated with ions during their production and handling. Therefore, measurements of the concentration of ions have become an important part of the material characterization of liquid crystals. Interestingly, even a brief analysis of existing publications can reveal a quite broad variability of the values of the concentration of ions measured by different research groups for the same liquid crystals. This reflects the complexity of ion generation mechanisms in liquid crystal materials and their dependence on numerous factors. In this paper, an overview of ion generation mechanisms in liquid crystals and modern ion measurement techniques is followed by the discussion of frequently overlooked factors affecting the measured values of the ion concentration. Ion-generating and ion-capturing properties of the alignment layers (or substrates) of liquid crystal cells are considered and used to evaluate a true concentration of ions in liquid crystals. In addition, practical recommendations aimed at improving the measurements of the ion density in liquid crystals are also discussed.

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