The Effects of Film Thickness, Light Polarization, and Light Intensity on the Light Transmission Characteristics of Thermochromic Liquid Crystals

2006 ◽  
Vol 129 (3) ◽  
pp. 372-378 ◽  
Author(s):  
Timothy B. Roth ◽  
Ann M. Anderson
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Light Intensity ◽  
Temperature Measurement ◽  
Light Transmission ◽  
Transmission Spectra ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Thermochromic Liquid Crystal ◽  
Thermochromic Liquid Crystals

Thermochromic liquid crystal materials change their crystalline structure and optical properties with temperature, making them useful in temperature measurement applications. This paper presents the results of a study to develop a temperature measurement system that uses light transmission through thermochromic liquid crystals instead of light reflection. We painted Hallcrest R25C10W sprayable liquid crystals on a clear surface and placed it in a spectrophotometer. The amount of light transmitted at monochromatic wavelengths from 400nm to 700nm was measured for temperatures from 25°C to 55°C under conditions of nonpolarized, linearly polarized, and cross-polarized light, for three light intensity levels, and three liquid crystal layer thicknesses. As the temperature was increased the amount of light transmitted through the liquid crystal layer increased. When the liquid crystals are in their active range the transmission spectra exhibit an s-curve shape and the percent of light transmitted through the liquid crystals at a fixed temperature increases with increasing wavelength. We detected significant changes in the transmission spectra for temperatures from 27°C to 48°C, whereas when used with reflected light the thermochromic liquid crystals are useful over a significantly smaller range. As the thickness of the thermochromic liquid crystal layer increases or as the incoming light intensity decreases, the amount of light transmitted through the liquid crystals decreases. We also investigated the effects of temperature overheat on the transmission spectra and found that heating the thermochromic liquid crystals above their active range increases the amount of light transmission. However, when the liquid crystals are cooled below their active range they return to their original state. We have analyzed the spectrophotometer data in a number of ways including: (a) total amount of light transmitted, (b) amount of red, green, and blue light transmitted; and (c) spectral curve shape characteristics (peak transmission, inflection wavelength and wavelength for peak transmission) all as a function of temperature. A linear relationship exists between temperature and all of these variables which we believe can be exploited for the development of a charge coupled light camera based light transmission system for temperature measurement.

scholarly journals Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 908
Author(s):  
Fabrizio Ciciulla ◽  
Annamaria Zaltron ◽  
Riccardo Zamboni ◽  
Cinzia Sada ◽  
Francesco Simoni ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Light Intensity ◽  
Lithium Niobate ◽  
Photovoltaic Effect ◽  
Optical Control ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Threshold Behaviour ◽  
All Optical

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 107 W/m2.

A Light Transmission Based Liquid Crystal Thermography System

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Timothy B. Roth ◽  
Ann M. Anderson
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Light Intensity ◽  
Light Transmission ◽  
Intensity Variation ◽  
Ccd Camera ◽  
Light Reflection ◽  
Transmission Characteristics ◽  
Lighting Conditions ◽  
Thermochromic Liquid Crystals

This paper presents results from a study aimed at developing a novel thermochromic liquid crystal (TLC) temperature measurement system that uses light transmission instead of light reflection to measure surface temperature fields. In previous work, we reported on the effect of temperature on light transmission through TLCs as measured with a spectrophotometer [Roth, T. B., and Anderson, A. M., 2005, “Light Transmission Characteristics of Thermochromic Liquid Crystals,” Proceedings of IMECE2005, Orlando, FL, Paper No. IMECE2005-81812;Roth, T. B., and Anderson, A. M., 2007, “The Effects of Film Thickness, Light Polarization and Light Intensity on the Light Transmission Characteristics of Thermochromic Liquid Crystals,” ASME J. Heat Transfer, 129(3), pp. 372–378]. Here we report on results obtained using a charge coupled device (CCD) camera and polychromatic light setup that is similar to the type of equipment used in TLC reflection thermography. We tested three different light sources, a white electroluminescent light, a green electroluminescent light, and a halogen fiber optic light, using both direct and remote lighting techniques. We found that the green signal (as detected by the CCD camera) of the green electroluminescent light makes the best temperature sensor, because under remote lighting conditions it showed a 500% linear signal increase as the temperature of the R25C10W TLCs was raised from 30°to48°C. We further found that the angle of the CCD camera relative to the light did not significantly affect the results for angles up to 10deg for remote lighting and 15deg for direct lighting. The effect of light intensity variation was not significant for intensities up to 40% of the original level when normalized on the intensity at 19°C (a temperature outside the active range of the TLCs). The use of light transmission results in a larger range of temperature over which the TLCs can be calibrated and offers opportunities for more uniform lighting conditions, which may help overcome some of the problems associated with light reflection.

Beobachtung von Inversionswänden in einer nematischen Flüssigkeit / Observation of inversion walls in nematic liquid, crystals

1973 ◽  
Vol 28 (6) ◽  
pp. 1044-1045 ◽  
Author(s):  
G. Heppke ◽  
F. Schneider
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Time Dependence ◽  
Nematic Liquid Crystal ◽  
Magnetic Field Direction ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Nematic Liquid Crystal Layer ◽  
The Magnetic Field

The magnetic field induced deformations of a homeotropic nematic liquid crystal layer are studied by means of the electric conductance. Its time dependence observed after rotating the magnetic field direction by 180° is explained by the formation of alignment inversion walls.

Dependence of transmission spectra on director orientation in the photonic crystal with a liquid crystal layer

2012 ◽  
Vol 8 (4) ◽  
pp. 277-279 ◽  
Author(s):  
Li-tao Song ◽  
Jie He ◽  
Hua-lei Wang ◽  
Yi-ang Han ◽  
Tao Li
Keyword(s):  
Liquid Crystal ◽  
Photonic Crystal ◽  
Transmission Spectra ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Director Orientation

scholarly journals Dissipative structures induced by photoisomerization in a dye-doped nematic liquid crystal layer

2018 ◽  
Vol 376 (2135) ◽  
pp. 20170382 ◽  
Author(s):  
I. Andrade-Silva ◽  
U. Bortolozzo ◽  
C. Castillo-Pinto ◽  
M. G. Clerc ◽  
G. González-Cortés ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Dissipative Structures ◽  
Input Power ◽  
Isotropic Phase ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Nematic Liquid Crystal Layer ◽  
Interface Propagation

Order–disorder phase transitions driven by temperature or light in soft matter materials exhibit complex dissipative structures. Here, we investigate the spatio-temporal phenomena induced by light in a dye-doped nematic liquid crystal layer. Experimentally, for planar anchoring of the nematic layer and high enough input power, photoisomerization processes induce a nematic–isotropic phase transition mediated by interface propagation between the two phases. In the case of a twisted nematic layer and for intermediate input power, the light induces a spatially modulated phase, which exhibits stripe patterns. The pattern originates as an instability mediated by interface propagation between the modulated and the homogeneous nematic states. Theoretically, the phase transition, emergence of stripe patterns and front dynamics are described on the basis of a proposed model for the dopant concentration coupled with the nematic order parameter. Numerical simulations show quite a fair agreement with the experimental observations. This article is part of the theme issue ‘Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 2)’.

Anchoring Induced by Porous Substrate on a Liquid Crystal Layer

1994 ◽  
Vol 239 (1) ◽  
pp. 257-261 ◽  
Author(s):  
Francesco Simoni ◽  
Ferdinando Basile ◽  
Francesco Bloisi ◽  
Luciano Vicari ◽  
Fouad Aliev
Keyword(s):  
Liquid Crystal ◽  
Crystal Layer ◽  
Porous Substrate ◽  
Liquid Crystal Layer
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