Liquid crystals to create colour changing coatings

Chameleons are famous for their colour-changing abilities. Inspired by this, scientists at the Pritzker School of Molecular Engineering (PME) at the University of Chicago have developed a way to stretch and strain liquid crystals to generate different colors. By creating a thin film of polymer filled with liquid crystal droplets and then manipulating it, they have determined the fundamentals for a colour-changing sensing system that could be used for smart coatings, sensors, and even wearable electronics. The research, led by Juan de Pablo, Liew Family Professor of Molecular Engineering.

Liquid crystals, which exhibit distinct molecular orientations, are already the basis for many display technologies. But de Pablo and his team were interested in chiral liquid crystals, which have twists and turns and a certain asymmetrical “handedness”—like right-handedness or left-handedness—that allows them to have more interesting optical behaviors.

“Possibilities are really open to the imagination”

These crystals can also form so-called “blue phase crystals,” which have the properties of both liquids and crystals and can in some cases transmit or reflect visible light better than liquid crystals themselves. The researchers knew that these crystals could potentially be manipulated to produce a wide range of optical effects if stretched or strained, but they also knew that it’s not possible to stretch or strain a liquid directly. Instead, they placed tiny liquid crystal droplets into a polymer film.
“That way we could encapsulate chiral liquid crystals and deform them in very specific, highly controlled ways,” de Pablo said. “That allows you to understand the properties they can have and what behaviors they exhibit.” By doing this, the researchers found many more different phases—molecular configurations of the crystals—than had been known before. These phases produce different colors based on how they are stretched or strained, or even when they undergo temperature changes.

“Now the possibilities are really open to the imagination,” de Pablo said. “Imagine using these crystals in a textile that changes color based on your temperature, or changes color where you bend your elbow.”

More information can be found on the website of the University of Chicago. The study has been published in Science Advances, Vol. 6, July 2020.

Image source: Pixabay.