Surprising twist in confined liquid crystals: A simple route to developing new sensors

March 24, 2017
A magnified image of liquid crystals confined to spherical tactoids. Credit: Georgia Tech

Researchers at Georgia Institute of Technology have found a material used for decades to color food items ranging from corn chips to ice creams could potentially have uses far beyond food dyes.

In a study published March 23 in the journal Proceedings of the National Academy of Sciences, the researchers described how a class of water soluble liquid crystals, called lyotropic chromonic liquid crystals, exhibited unexpected characteristics that could be harnessed for use in sensors and other potential 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 problem. "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 the Georgia Tech 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."

Georgia Tech students Jinxin Fu and Rui Chang view the liquid crystals created from a common food dye. Credit: Rob Felt

The researchers then used a simple model of the aggregation behavior of these molecules to explain these surprising results. Further, spectroscopic experiments using polarized Raman microscopy were performed to confirm their findings.

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. The material's responsiveness to altering its environment could potentially be used to sense the chirality—or "handedness"—of molecules, Srinivasarao said.

"These materials don't have a chiral center but they exhibit a chiral structure," Srinivasarao said. "That in itself is very interesting."

Georgia Tech students Jinxin Fu and Rui Chang with Mohan Srinivasarao, a professor in the Georgia Tech School of Materials Science and Engineering, Credit: Rob Felt

That finding could be useful in answering those kinds of questions, he said.

"There are lots of people studying why on planet Earth all amino acids have a handedness, one and not the other," Srinivasarao said. "Where does this handedness come from?"

Explore further: Research reveals inner workings of liquid crystals

More information: Karthik Nayani et al, Using chiral tactoids as optical probes to study the aggregation behavior of chromonics, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1614620114

Related Stories

Research reveals inner workings of liquid crystals

March 20, 2017

Liquid crystals are used in everything from tiny digital watches to huge television screens, from optical devices to biomedical detectors. Yet little is known of their precise molecular structure when portions of such crystals ...

Research team discovers new liquid crystal configurations

April 1, 2015

Oil-based liquid crystals are ubiquitous; a deep understanding of their properties is behind the displays found in most computer monitors, televisions and smartphones. Water-based liquid crystals are less well understood, ...

New theory on liquid crystals with high symmetry

November 8, 2016

LCD screens use liquid crystals, which have a high degree of order, even though they form a fluid. A new theory detailed in Physical Review X maps out the interplay between order, temperature and symmetry.

Superior crystals grown from levitating droplets

December 6, 2016

Crystals that don't experience mechanical stress during growth have superior quality. Levitating liquid metal is the idea behind the project 'Perfecting metal crystals' led by the University of Twente in the Netherlands.

Recommended for you

A curious quirk brings organic diode lasers one step closer

November 20, 2017

Since their invention in 1962, semiconductor diode lasers have revolutionized communications and made possible information storage and retrieval in CDs, DVDs and Blu-ray devices. These diode lasers use inorganic semiconductors ...

Carefully crafted light pulses control neuron activity

November 17, 2017

Specially tailored, ultrafast pulses of light can trigger neurons to fire and could one day help patients with light-sensitive circadian or mood problems, according to a new study in mice at the University of Illinois.

Strain-free epitaxy of germanium film on mica

November 17, 2017

Germanium, an elemental semiconductor, was the material of choice in the early history of electronic devices, before it was largely replaced by silicon. But due to its high charge carrier mobility—higher than silicon by ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.