Liquid crystals already provide the basis for successful technologies such as LCD displays, and researchers continue to create specific types of liquid crystals for better optical devices and applications.
Juan de Pablo, the Liu family professor of molecular engineering at the University of Chicago’s Pritzker School of Molecular Engineering (PME), and his team have now found a way to create and stabilize so-called “blue phase liquid crystals” that have properties of both liquids and crystals, and in some cases can better reflect visible light. of ordinary liquid crystals.
The results are published in ACS nanoIt could lead to new optical technologies with better response times.
A new method for stabilizing blue-phase crystals
Thanks to their uniform molecular orientation, liquid crystals are the basis for many display technologies, including those found in digital displays of computers and televisions. In this research, de Pablo and his team were interested in chiral liquid crystals, which have a specific type of asymmetrical “hand” – such as right or left hand – that allows them to show a wider and more interesting range of visual behaviours.
Most importantly, these crystals can form blue-phase crystals, which, due to their unique structure, can reflect blue and green light, and can be turned on and off at an amazing speed. But these crystals exist only in a small range of temperatures and are inherently unstable: heating them to even one degree can destroy their properties. This has limited their use in technologies.
Through simulations and experiments, the team was able to stabilize blue-phase crystals by forming so-called double emulsions. They used a small droplet of an aqueous solution surrounded by an outer drop of a helical oil liquid crystal, creating a “core and shell” structure. This same structure was suspended in another water-based liquid, immiscible with liquid crystal. During the appropriate range of temperatures, they were able to trap the chiral liquid crystal in the shell in a “blue phase” state. Then they formed a polymer network inside the shell, stabilizing the blue crystal without destroying its properties.
Make perfect crystals
The team then showed that they could change the temperature of the blue phase crystal by 30 degrees without destroying it. Not only that, the process formed perfect and uniform blue phase crystals, allowing researchers to better predict and control their behavior.
“Now that we understand these materials and can control them, we can take advantage of their unique optical properties,” de Pablo said. “The next step is to deploy it in devices and sensors to prove its usefulness.”
Potential applications include display technologies that can be turned on and off with very small changes in size, temperature, or exposure to light, or sensors that can detect radiation within a given wavelength.
Liquid crystals create easy-to-read, color-changing sensors
Monirosadat Sadati et al, Control of polymer-stabilized single-band cubic nanocrystals from chiral filaments by confinement, ACS nano (2021). DOI: 10.1021 / acsnano.1c04231
Presented by the University of Chicago
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