Liquid crystals already form the basis of successful technologies such as LCD monitors, and scientists continue to create specific kinds of liquid crystals for even better optical devices and applications.
Juan de Pablo, Liew family professor of molecular engineering at the Pritzker School of Molecular Engineering (PME) at the University of Chicago, and his team have now found a way to create and stabilize so-called “blue phase liquid crystals”, which have the properties of both liquids and crystals, and in some cases may reflect visible light better than ordinary liquid crystals.
The results, published in ACS Nano, could lead to new optical technologies with better response times.
A new method of stabilizing blue phase crystals
Thanks to their uniform molecular orientation, liquid crystals are already the basis of many display technologies, including those in digital screens for computers and televisions. In this research, de Pablo and his team were interested in chiral liquid crystals, which have a certain asymmetric “hand” – such as right-handed or left-handed – that allows them to exhibit a wider and more interesting range of optical behaviors.
It is important that these crystals can form blue phase crystals, which due to their unique structure can reflect blue and green light, and they can be turned on and off incredibly quickly. However, these crystals exist only in a small temperature range and are inherently unstable: Heating themselves to a degree can destroy their properties. It has limited their use in technologies.
Through simulation and experiments, the team was able to stabilize the blue phase crystals through the formation of so-called double emulsions. They used a small droplet of a water-based solution surrounded by an outer droplet of an oily chiral liquid crystal, thereby creating a “core and shell” structure. This structure was itself suspended in another water-based liquid that could not be mixed with the liquid crystal. Above the appropriate temperature range, they were able to capture the chiral liquid crystal in the shell in a “blue phase” state. They then formed a polymer network in the shell, which stabilized the blue crystal without destroying its properties.
Creates 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, uniform blue-phase crystals, which enabled 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 implement them in devices and sensors to demonstrate their applicability.”
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 certain wavelength.
Liquid crystals create easy-to-read, color-changing sensors
Monirosadate Sadati et al, Control of monodomain polymer-stabilized cubic nanocrystals of chiral nematode by entrapment, ACS Nano (2021). DOI: 10.1021 / acsnano.1c04231
Provided by the University of Chicago
Citation: Stabilized Blue Phase Crystals Can Lead to New Optical Technologies (2021, November 2) Retrieved November 3, 2021 from https://phys.org/news/2021-11-stabilized-blue-phase-crystals-optical.html
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