Campus researchers make 1st direct measurements of liquid crystals’ molecular structure

Mikaela Raphael/Staff

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Using an avant-garde X-ray technique, Lawrence Berkeley National Laboratory researchers recently made the first direct measurements of liquid crystals’ molecular structure — marking possible performance improvements to liquid-crystal displays in smartphone and computer screens.

While researchers knew that liquid crystals come in various structures such as a naturally spiraling “twist-bend” molecular arrangement, campus researchers have recorded measurements that confirm the arrangements’ existence.

The X-ray technique, which was developed at the Advanced Light Source at Berkeley Lab over the last few years, uses low-energy X-rays to examine carbon atoms in the liquid crystal molecules to show the orientation of their chemical bonds and a strongly coiled structure is very rare.

“We have developed a measurement capability, using soft x-rays that reveals (the) shape and functionality of materials, that was perfect for this experiment,” said ALS Director Roger Falcone in an email.

Liquid crystals have a variety of uses, but they are most known for their applications in smartphone and computers screens, called liquid-crystal displays, or LCDs. The market of LCDs tops over one-third of the revenue in the overall electronic screen market.

“A few other places are trying to develop (the technique),” said Chenhui Zhu, lead author of the research paper published April 7 in the Physical Review Letters, but he added the campus team is the first to use it to study this liquid-crystal phase.

The findings could lead to improved LCD performance, such as expediting how fast light switches on and off in a tiny range or helping explain chiral structures molecules with asymmetric properties that aid researchers in chemistry, biology and materials science fields.

In addition, the measurements will advance scientists’ understanding of liquid crystals’ properties, such as how the material responds to variations in UV light and stress, Zhu said. The next step, he added, is using the X-ray technology in related industries.

“On one hand, it gives insight,” Zhu said. “On the other hand, it can be very easily expanded to studying other materials.”

Because the reason behind why the material naturally forms in a tight spiral arrangement remains unclear, Zhu said further research is needed to better understand the liquid crystal structure.

Using this new X-ray technique, Zhu intends to look into other spiraling structures such as the helical nanofilament, which is a liquid crystal phase that could lead to advancements in solar energy developments.

“This is an elegant experiment demonstrating that the twist in these liquid crystal systems occurs over a remarkably short distance,” said former UC Berkeley chancellor and current physics, materials science and engineering professor Robert Birgeneau, in an email. “This work opens up a new distance regime. It will be interesting to see if novel applications emerge.”

Contact Danwei Ma at [email protected].