“Now that we understand these materials and can control them, we can take advantage of their unique optical properties. The next step is deploying them in devices and sensors to demonstrate their usefulness.”Juan de Pablo, University of Chicago
Liquid crystals already provide the basis for successful technologies like liquid crystal displays (LCDs), and researchers continue to create specific kinds of liquid crystals for even better optical devices and applications.
Now, a team of researchers led by Juan de Pablo, professor of molecular engineering in the Pritzker School of Molecular Engineering (PME) at the University of Chicago, has found a way to create and stabilize so-called 'blue phase liquid crystals'. These possess the properties of both liquids and crystals, and can in some cases reflect visible light better than ordinary liquid crystals, potentially leading to new optical technologies with better response times. The researchers report their work in a paper in ACS Nano.
Thanks to their uniform molecular orientation, liquid crystals are already the basis for many display technologies, including those in digital displays for computers and televisions. In this study, de Pablo and his team were interested in chiral liquid crystals, which have a certain asymmetrical 'handedness' – like right-handedness or left-handedness – that allows them to exhibit a wider and more interesting range of optical behaviors.
Importantly, these crystals can form blue phase crystals, which, because of their unique structure, can reflect blue and green light, and can be switched on and off incredibly quickly. But these crystals only exist over a small range of temperatures and are inherently unstable – heating them up by even 1°C can destroy their properties – which has limited their use in technologies.
Through simulation and experiments, the researchers were able to stabilize the blue phase crystals through the formation of so-called double emulsions. They used a small core droplet of a water-based solution surrounded by an outer droplet of an oily chiral liquid crystal, thereby creating a 'core and shell' structure.
That structure was itself suspended in another water-based liquid that was unmixable with the liquid crystal. Over the appropriate range of temperatures, they were able to trap the chiral liquid crystal in the shell in a 'blue phase' state. They then formed a polymer network within the shell, which stabilized the blue crystal without destroying its properties.
The researchers showed that they could change the temperature of this blue phase crystal by 30°C without destroying it. What is more, the process formed perfect, uniform blue phase crystals, which allowed the 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 deploying them in devices and sensors to demonstrate their usefulness.”
Potential applications of these blue phase liquid crystals include display technologies that could be turned on and off with very small changes in size and temperature or exposure to light, and sensors that can detect radiation within a certain wavelength.
This story is adapted from material from the University of Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.