Effect of cell thickness on the electro-optic response of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy

2020 ◽  
Author(s):  
Kyung Min Lee ◽  
Ecklin P. Crenshaw ◽  
Mariacristina Rumi ◽  
Timothy J. White ◽  
Timothy J. Bunning ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Dielectric Anisotropy ◽  
Cholesteric Liquid Crystals ◽  
Electro Optic ◽  
Polymer Stabilized ◽  
Cell Thickness

scholarly journals Effect of Cell Thickness on the Electro-optic Response of Polymer Stabilized Cholesteric Liquid Crystals with Negative Dielectric Anisotropy

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 746 ◽  
Author(s):  
Kyung Min Lee ◽  
Ecklin P. Crenshaw ◽  
Mariacristina Rumi ◽  
Timothy J. White ◽  
Timothy J. Bunning ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Field Strength ◽  
Polymer Network ◽  
Dielectric Anisotropy ◽  
Cholesteric Liquid Crystals ◽  
Colored State ◽  
Electro Optic ◽  
Dc Electric Field ◽  
Polymer Stabilized ◽  
Cell Thickness

It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC) electric field. The field-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin films (≤5 μm). Increasing the DC field strength redshifts the reflection notch to longer wavelength until the reflection disappears at high DC fields. The extent of the tuning range is dependent on the cell thickness. The transition from the reflective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the field-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC field strength, various reflection wavelengths can be addressed from either a different reflective (colored) state at 0 V or a transparent state at a high DC field. Relatively fast responses (~50 ms rise times and ~200 ms fall times) are observed for these thin PSCLCs.

Enhanced reflection band broadening in polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy

2018 ◽  
Vol 267 ◽  
pp. 120-126 ◽  
Author(s):  
Hossein Nemati ◽  
Shiyi Liu ◽  
Alireza Moheghi ◽  
Vincent P. Tondiglia ◽  
Kyung Min Lee ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Dielectric Anisotropy ◽  
Band Broadening ◽  
Cholesteric Liquid Crystals ◽  
Reflection Band ◽  
Polymer Stabilized

Blue-shifting tuning of the selective reflection of polymer stabilized cholesteric liquid crystals

Soft Matter ◽  
2017 ◽  
Vol 13 (35) ◽  
pp. 5842-5848 ◽  
Author(s):  
Kyung Min Lee ◽  
Vincent P. Tondiglia ◽  
Nicholas P. Godman ◽  
Claire M. Middleton ◽  
Timothy J. White
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystal ◽  
Dielectric Anisotropy ◽  
Cholesteric Liquid Crystals ◽  
Large Magnitude ◽  
Selective Reflection ◽  
Polymer Stabilized

We report on electrically-induced, large magnitude (>300 nm), and reversible tuning of the selective reflection in polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy nematic liquid crystal hosts.

scholarly journals Effect of Ion Concentration on the Electro-Optic Response in Polymer-Stabilized Cholesteric Liquid Crystals

Crystals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 7
Author(s):  
Kyung M. Lee ◽  
Timothy J. Bunning ◽  
Timothy J. White ◽  
Michael E. McConney ◽  
Nicholas P. Godman
Keyword(s):  
Liquid Crystals ◽  
Polymer Network ◽  
Ion Concentration ◽  
Cholesteric Liquid Crystals ◽  
Reflection Band ◽  
Ion Density ◽  
Electro Optic ◽  
Order Of Magnitude ◽  
Polymer Stabilized ◽  
Bandwidth Broadening

We have previously reported that the application of a DC field can adjust the position and/or bandwidth of the selective reflection notch in polymer-stabilized cholesteric liquid crystals (PSCLCs). The proposed mechanism of these electro-optic (EO) response is ion-facilitated electromechanical deformation of the polymer stabilizing network. Accordingly, the concentration of ions trapped within the polymer network should considerably influence the EO response of PSCLC. Our prior studies have indicated that photoinitiators can increase ion density in PSCLC by an order of magnitude. Here, we isolate the contribution of ionic impurities associated with liquid crystal monomers (LCMs) by utilizing initiator-less polymerization. PSCLCs prepared with LCM with low ion concentration show bandwidth broadening of the reflection band whereas PSCLCs prepared with LCM with high ion concentration exhibit a red shifting tuning of the reflection band. The extent of the tuning or bandwidth broadening of the CLC reflection band depends on the concentration of LCMs and the chirality of the LCM.

Large range electrically-induced reflection notch tuning in polymer stabilized cholesteric liquid crystals

2015 ◽  
Vol 3 (34) ◽  
pp. 8788-8793 ◽  
Author(s):  
Kyung Min Lee ◽  
Vincent P. Tondiglia ◽  
Taewoo Lee ◽  
Ivan I. Smalyukh ◽  
Timothy J. White
Keyword(s):  
Liquid Crystals ◽  
Direct Current ◽  
Large Range ◽  
Dielectric Anisotropy ◽  
Cholesteric Liquid Crystals ◽  
Large Magnitude ◽  
Polymer Stabilized

This communication reports large magnitude (exceeding 1500 nm) and reversible reflection notch tuning in polymer stabilized cholesteric liquid crystals (PSCLCs) formulated with negative dielectric anisotropy (−Δε) hosts upon application of a direct current (DC) field.

Electro-optic response in holographic polymer stabilized cholesteric liquid crystals

2020 ◽  
Author(s):  
Kyung Min Lee ◽  
Vincent P. Tondiglia ◽  
Timothy J. White ◽  
Timothy J. Bunning ◽  
Michael E. McConney
Keyword(s):  
Liquid Crystals ◽  
Cholesteric Liquid Crystals ◽  
Electro Optic ◽  
Polymer Stabilized

Electro-optic response in polymer stabilized cholesteric liquid crystals

2021 ◽  
Author(s):  
Kyung Min Lee ◽  
Timothy J. White ◽  
Timothy J. Bunning ◽  
Michael E. McConney ◽  
Nicholas Godman
Keyword(s):  
Liquid Crystals ◽  
Cholesteric Liquid Crystals ◽  
Electro Optic ◽  
Polymer Stabilized

Cell thickness dependence of electrically tunable infrared reflectors based on polymer stabilized cholesteric liquid crystals

2017 ◽  
Vol 61 (5) ◽  
pp. 745-751 ◽  
Author(s):  
Xiaowen Hu ◽  
Laurens T. de Haan ◽  
Hitesh Khandelwal ◽  
Albertus P. H. J. Schenning ◽  
Li Nian ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Thickness Dependence ◽  
Cholesteric Liquid Crystals ◽  
Polymer Stabilized ◽  
Cell Thickness

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.

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