Electrohydrodynamic Effects in Cholesteric Liquid Crystals under ac Electric Fields

1972 ◽  
Vol 28 (12) ◽  
pp. 735-737 ◽  
Author(s):  
F. Rondelez ◽  
H. Arnould ◽  
C. J. Gerritsma
Keyword(s):  
Liquid Crystals ◽  
Electric Fields ◽  
Cholesteric Liquid Crystals ◽  
Ac Electric Fields

ELECTRO-OPTICAL PHENOMENA DUE TO INFLUENCE OF LIGHT BEAMS ON MATERIAL PARAMETERS OF LIQUID CRYSTALS

1999 ◽  
Vol 08 (03) ◽  
pp. 389-401 ◽  
Author(s):  
NELSON V. TABIRYAN ◽  
CESARE UMETON
Keyword(s):  
Liquid Crystals ◽  
Electric Fields ◽  
Diffusion Processes ◽  
Material Parameters ◽  
Ac Electric Fields ◽  
Absorption Of Light ◽  
Optical Phenomena ◽  
Light Beams

Modulation of material parameters of liquid crystals (LC) due to absorption of light beams allows to control the reorientation of the LC under the influence of ac electric fields. Particularly, it makes possible recording of photorefractive-like orientation gratings. Such gratings are phase shifted with respect to the pattern of interfering light beams. The material and external parameters determine the magnitude of the shift. These photorefractive-like phase shifted gratings are stationary, and no diffusion processes are involved in their build-up.

Cholesteric liquid crystals with an electrically controllable reflection bandwidth based on ionic polymer networks and chiral ions

2015 ◽  
Vol 3 (21) ◽  
pp. 5406-5411 ◽  
Author(s):  
Hongbo Lu ◽  
Jinliang Hu ◽  
Yutian Chu ◽  
Wei Xu ◽  
Longzhen Qiu ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Electric Fields ◽  
Polymer Networks ◽  
Cholesteric Liquid Crystals ◽  
Ionic Polymer ◽  
Visible Wavelength

The reflection bandwidth can be tuned dynamically by electric fields in the visible wavelength regime.

scholarly journals Dynamic FT-IR spectroscopy of liquid crystals and polymer films

1993 ◽  
Author(s):  
Βασίλειος Γρηγορίου
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Electric Fields ◽  
Polymer Films ◽  
Spectroscopic Techniques ◽  
Ac Electric Fields ◽  
Pulsed Dc ◽  
Ft Ir ◽  
Reorientation Dynamics ◽  
Director Reorientation

This dissertation describes the use of continuous-scan and step-scan Fourier transform infrared (FT-IR) spectroscopic techniques to study the dynamics of the response of polymer films and liquid crystals to external perturbations. The investigation of liquid crystals includes both nematic and chiral smectic C examples. In these studies the dynamic infrared absorbance is used to explore the submolecular (functional group) contributions to the reorientation dynamics of the liquid crystal director in response to both pulsed (DC) and modulated (AC) electric fields. Continuous-scan stroboscopic FT-IR and step-scan impulse-response FT-IR were used to analyze the rise dynamics of reorientation resulting from pulsed DC perturbations; whereas step-scan FT-IR was used to monitor both rise and decay processes in response to synchronously modulated (AC) electric fields. In the step-scan measurements this sub-molecular view of the dynamics of liquid crystal director reorientation was enhanced by frequency correlation analysis, to yield 2D FT-IR spectra. For the nematic liquid crystal 4-pentyl-4$\sp\prime$-cyanobiphenyl (5CB) the data suggest a different rate of response of the rigid and floppy parts of the LC molecules. The second application of dynamic step-scan FT-IR reported is the study of the response of various polymer films to sinusoidally modulated tensile strain. The main advantage of the technique is that it can provide valuable information at the molecular level that can be used to interpret the macroscopic properties of the polymeric material under investigation. Examples of application to different types of polymer films are presented. Results for several heterogeneous polymers including semicrystalline high density/low density polyethylene blends, the micro-phase separated copolymer Kraton$\sp\circler$ and a homogeneous polymer blend of polystyrene/polydimethylphenylene oxide are presented. Finally, the modification of a research-grade FT-IR spectrometer (Nicolet Instruments, System 800) for step-scan operation is described. Some applications of the instrument to photoacoustic spectroscopy (PAS) are presented.

Dynamics of selective reflections of cholesteric liquid crystals subject to electric fields

1995 ◽  
Vol 77 (2) ◽  
pp. 572-576 ◽  
Author(s):  
N. Scaramuzza ◽  
C. Ferrero ◽  
V. Carbone ◽  
C. Versace
Keyword(s):  
Liquid Crystals ◽  
Electric Fields ◽  
Cholesteric Liquid Crystals

Mechanism of electrically induced photonic band gap broadening in polymer stabilized cholesteric liquid crystals with negative dielectric anisotropies

Soft Matter ◽  
2015 ◽  
Vol 11 (6) ◽  
pp. 1208-1213 ◽  
Author(s):  
Hossein Nemati ◽  
Shiyi Liu ◽  
Rafael S. Zola ◽  
Vincent P. Tondiglia ◽  
Kyung Min Lee ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Band Gap ◽  
Electric Fields ◽  
Photonic Band Gap ◽  
Cholesteric Liquid Crystals ◽  
Reflection Band ◽  
Polymer Stabilized ◽  
Photonic Band ◽  
Dc Electric Fields

We experimentally observed that the photonic band gap (reflection band) of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropies can be greatly broadened under DC electric fields.

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