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The Dye Is Re-Cast

Two researchers in a lab, one looking into a microscope lens with a picture projected onto a computer screen nearby

Georgia Tech students Jinxin Fu and Rui Chang view liquid crystals created from a common food dye.

By Josh Brown

A material used for decades to color food items could potentially have a new use.

In a study published in the journal Proceedings of the National Academy of Sciences, researchers described how a class of water soluble materials, called lyotropic chromonic liquid crystals, exhibited unexpected characteristics that could be harnessed for use in sensors and other applications.

“We were seeking to understand the aggregation and phase behavior of these plank-like molecules as a function of temperature and concentration,” said Karthik Nayani, a former Georgia Tech student who worked on the study. “When observed under crossed polarizers in an optical microscope, liquid crystals can exhibit beautiful textures that hint toward how the molecules themselves are arranged.”

To answer some fundamental questions pertaining to the material’s phase behavior, the researchers used the microscopes to observe the molecules’ textures when they were confined to droplets known as tactoids.

“Surprisingly, we found a configuration that hasn’t been seen before in the 70 years that people have been studying liquid crystals,” said Mohan Srinivasarao, a professor in Georgia Tech’s School of Materials Science and Engineering. “Historically, liquid crystals in tactoids conform to what is known as a bipolar and a bipolar configuration with a twist. At lower concentrations, we found that these liquid crystals arrange in a concentric fashion, but one that appears to be free of a singular defect.”

These new findings add to the growing understanding of how chromonic liquid crystals could be used in sensing applications, Srinivasarao said. The crystals are water soluble and respond dramatically to being confined to certain patterns — such as tactoidal droplets — concentrations, and temperatures.

Related: Surprising twist in confined liquid crystals: A simple route to developing new sensors, March 24, 2017

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