Liquid crystals already offer the foundation for effective technologies such as LCD displays, and scientists continue to develop specific types of liquid crystals for much better optical applications and devices.
Prof. Juan de Pablo. Image Credit: University of Chicago
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 recently discovered a way to produce and stabilize so-called “blue phase liquid crystals,” which have the properties of both crystals and liquids, and can, in certain cases, reflect visible light better than regular liquid crystals.
The findings, reported in ACS Nano, could pave the way to new optical technologies with improved response times.
A New Method for Stabilizing Blue Phase Crystals
Owing to their even molecular orientation, liquid crystals are already the foundation for numerous display technologies, including those in digital displays for televisions and computers. In this study, de Pablo and his team were keen to work with chiral liquid crystals, which possess a specific asymmetrical “handedness” — like right-handedness or left-handedness — that enables them to display a broader and more stimulating range of optical behaviors.
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, Liew Family Professor of Molecular Engineering, Pritzker School of Molecular Engineering, University of Chicago
Significantly, these crystals can develop blue phase crystals, which, due to their unique structure, can reflect blue and green light, and can be turned on and off extremely fast. Nevertheless, these crystals are only present in a small range of temperatures and are fundamentally unstable: heating them up by even 1 degree can ruin their properties. That has restricted their application in technologies.
Through simulation and trials, the researchers could stabilize the blue phase crystals through the creation of so-called double emulsions. They used a tiny core droplet of a water-based solution surrounded by an outer droplet of an oily chiral liquid crystal, thus forming a “core and shell” structure. This structure was then suspended in another water-based liquid, unmixable with the liquid crystal.
Over a suitable range of temperatures, they were able to capture the chiral liquid crystal in the shell in a “blue phase” state. They then created a polymer network within the shell, which stabilized the blue crystal without ruining its properties.
Creating Perfect Crystals
The team then demonstrated that they could modify the temperature of the blue phase crystal by 30 degrees without ruining it. In addition to that, the process created perfectly formed blue phase crystals, which enabled the team to better predict and regulate their behavior.
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, Liew Family Professor of Molecular Engineering, Pritzker School of Molecular Engineering, University of Chicago
Potential future applications include display technologies that can be switched on and off with very small variations in temperature, size or exposure to light, or sensors that can sense radiation within a specific wavelength.
Other authors on the paper are Jose A. Martinez-Gonzalez, Monirosadat Sadati, Sepideh Norouzi, Alexander Cohen, and Orlando Guzmán.
Journal Reference
Sadati, M., et al. (2021) Control of Monodomain Polymer-Stabilized Cuboidal Nanocrystals of Chiral Nematics by Confinement. ACS Nano. doi.org/10.1021/acsnano.1c04231.