Scientists at the Pritzker School of Molecular Engineering (PME) at the University of Chicago (UChicago) (Chicago, Illinois, USA) have developed a polymer film filled with liquid crystals that generates different colors when they are stretched or strained. This material was inspired by the color-changing abilities of chameleons, who have nanocrystals on their skins that expand or contract depending on body temperature or mood.
The team of scientists at UChicago believe that this color-changing sensing system could have applications for smart coatings, sensors, and wearable electronics. Led by Juan de Pablo, Liew Family Professor of Molecular Engineering, the UChicago team has published the results of their research in the July 10 edition of Science Advances.
The de Pablo-led team focused on chiral liquid crystals, which differ from conventional liquid crystals in that they have twists and turns and a certain asymmetrical “handedness”—similar to left- or right-handedness in humans—that imbues them with additional optical behaviors. In addition, chiral liquid crystals can also form “blue phase crystals” that have the properties of both liquids and crystals, along with the added ability of transmitting and reflecting light better than liquid crystals.
The team knew they could manipulate chiral liquid crystals to produce a wide range of optical effects—but rather than doing so directly, they placed tiny liquid crystal drops into a polymer film. “That way we could encapsulate chiral liquid crystals and deform them in very specific, highly controlled ways,” de Pablo says. “That allows you to understand the properties they can have and what behaviors they exhibit.”
In doing so, the team discovered different molecular configurations, or phases, of the crystals and found that they produced different colors based on how they were stretched or strained, or when they underwent temperature changes. “Now the possibilities are really open to the imagination,” says de Pablo. “Imagine using these crystals in a textile that changes color based on your temperature, or changes color where you bend your elbow.”
“You could just look at the color of your device and know how much strain that material or device is under and take corrective action as needed,” he adds. “For example, if a structure is under too much stress, you could see the color change right away and close it down to repair it. Or if a patient or an athlete placed too much strain on a particular body part as they move, they could wear a fabric to measure it and then try to correct it.”
In addition to strain and temperature, the material also the potential to be affected by voltage, magnetic field, and acoustic fields, which could lead to further applications of these crystals. “Now that we have the fundamental science to understand how these materials behave, we can start applying them to different technologies,” says de Pablo.
Source: University of Chicago, https://news.uchicago.edu/