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  • Novel Mixes Expand Operating Temperature Range for LCDs

Photonics.com
Apr 2016
ORLANDO, Fla., April 8, 2016 — An experimental liquid crystal (LC) mixture has been shown to function properly in temperature range of −40 to about 100 °C, an improvement over current technologies used in automobile displays, smartphones and televisions, for example, which grow blurry and sluggish in extreme temperatures.

A team of researchers led by professor Shin-Tson Wu at the University of Central Florida formulated three new liquid crystal mixtures with a wide nematic range, small visco-elastic coefficient and low activation energy.

Professor Shin-Tson Wu and doctoral students work on liquid crystal mixtures in his lab at the University of Central Florida's College of Optics & Photonics.
Professor Shin-Tson Wu and doctoral students work on liquid crystal mixtures in his lab at the University of Central Florida's College of Optics & Photonics. From left, Fenglin Peng, Yuge "Esther" Huang, Wu and Fangwang "Grace" Gou. Courtesy of the University of Central Florida.

In addition, the LC pixels are able to change their brightness level about 20 times faster than required by European automotive standards, the researchers said.

The LC mixes used four major ingredients, described in a study published in open access format in Optical Materials Express (doi: 10.1364/ome.6.000717). The homologues of Compound 1 showed high birefringence and large dielectric anisotropy; however, their viscoelastic coefficient and activation energy were relatively large.

To reduce viscosity, the researchers doped about 50 percent nonpolar diluters (i.e. Compound 2 [18, 19]). Compounds 3 and 4 (about 30 percent) were added to obtain high clearing point and wide nematic range. Phase transition temperatures were measured by differential scanning calorimetry.

The team said these LCs could greatly improve the performance of different display devices in a car, such as a head-up projection using liquid-crystal-on-silicon with an average gray-to-gray (GTG) response time less than 1 ms at an elevated temperature. The average GTG response time was maintained at about 10 ms for fringing field switching LCD at 0 °C, and also about 10 ms for twisted nematic LCD at −20 °C.

Wu previously contributed to the development of LCDs for smartphones and other devices that are readable in sunlight, and is currently working on a smart brightness control film that has applications for automobiles, planes, eyewear, windows and more.


GLOSSARY
liquid crystal
A type of material that possesses less geometrical regularity or order than normal solid crystals, and whose order varies in response to alterations in temperature and other quantities. Liquid crystals are characterized by phase varieties, including cholesteric, nematic and smectic. The optical properties of liquid crystals are familiar from their use in displays, known as LCDs.
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