Electric Field Induced Biaxial Order and Differential Quenching of Uniaxial Fluctuations in a Nematic with Negative Dielectric Anisotropy

2012 ◽  
Vol 559 (1) ◽  
pp. 97-105 ◽  
Author(s):  
Volodymyr Borshch ◽  
Sergij V. Shiyanovskii ◽  
Oleg D. Lavrentovich
Keyword(s):  
Electric Field ◽  
Dielectric Anisotropy ◽  
Differential Quenching

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.

Voltage-Induced Cholesteric Structure-Transformation in Thin Layers

1981 ◽  
Vol 36 (7) ◽  
pp. 718-726 ◽  
Author(s):  
Paul R. Gerber
Keyword(s):  
Liquid Crystals ◽  
Electric Field ◽  
Thin Layers ◽  
Dielectric Anisotropy ◽  
Structure Transformation ◽  
Cholesteric Liquid Crystals ◽  
Threshold Voltages

Abstract o lta g e -In d u c e d C h o le s te r ic S tr u c tu r e -T r a n s f o r m a tio n in T h i n L a y e rs Measurements of various threshold voltages which occur in thin layers of cholesteric liquid crystals with positive dielectric anisotropy under homeotropic wall-alignment conditions are presented. Characteristic times are determined for some of the structure-changing processes which take place under application of electric-field changes. The measurements have been performed for various pitch-to-thickness ratios, and are expressed in empirical formulae.

Surface-Induced Flexoelectric Domains in Asymmetrically Strong-Weak Anchored MBBA Films

1982 ◽  
Vol 37 (4) ◽  
pp. 334-341
Author(s):  
H. P. Hinov
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Dielectric Anisotropy ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Surface Anchoring ◽  
Threshold Voltages ◽  
Domain Period ◽  
Cell Thickness

Abstract The longitudinal surface-induced flexoelectric domains, previously obtained in symmetrically weak-anchored nematic layers have been further investigated in asymmetrically strong-weak anchored MBBA layers. The threshold voltages indicating the onset of the flexoelectric instabilities are high for thin cells (d = 9 μm, Uth = 10 V) and small for thick cells (d = 150 μm, Uth =1.5 V). Pronounced minima in the curves p vs. d and Uth vs. d, where p is the domain period and d is the cell thickness, were obtained. The flexoelectric domains were replaced by electrohydrodynamic instabilities only in the case of strong azimuthal anchoring of the liquid crystal layer.The role of the sign and the value of the dielectric anisotropy, the homogeneity of the electric field as well as the asymmetry in the surface anchoring are discussed in detail.

scholarly journals Dielectric and Electro-Optic Effects in a Nematic Liquid Crystal Doped with h-BN Flakes

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 123 ◽  
Author(s):  
Rajratan Basu ◽  
Lukas J. Atwood ◽  
George W. Sterling
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Nematic Liquid Crystal ◽  
Hexagonal Boron Nitride ◽  
Honeycomb Structure ◽  
Dielectric Anisotropy ◽  
Isotropic Phase ◽  
Electro Optic ◽  
Anchoring Strength ◽  
Director Reorientation

A small quantity of hexagonal boron nitride (h-BN) flakes is doped into a nematic liquid crystal (LC). The epitaxial interaction between the LC molecules and the h-BN flakes rising from the π−π electron stacking between the LC’s benzene rings and the h-BN’s honeycomb structure stabilizes pseudo-nematic domains surrounding the h-BN flakes. Electric field-dependent dielectric studies reveal that the LC-jacketed h-BN flakes follow the nematic director reorientation upon increasing the applied electric field. These anisotropic pseudo-nematic domains exist in the isotropic phase of the LC+h-BN system as well, and interact with the external electric field, giving rise to a nonzero dielectric anisotropy in the isotropic phase. Further investigations reveal that the presence of the h-BN flakes at a low concentration in the nematic LC enhances the elastic constants, reduces the rotation viscosity, and lowers the pre-tilt angle of the LC. However, the Fréedericksz threshold voltage stays mostly unaffected in the presence of the h-BN flakes. Additional studies show that the presence of the h-BN flakes enhances the effective polar anchoring strength in the cell. The enhanced polar anchoring strength and the reduced rotational viscosity result in faster electro-optic switching in the h-BN-doped LC cell.

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.

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