Artificial Chameleons. Color-changing gas sensors. Kindles that display images in color.
These futuristic technologies could be possible with blue phase liquid crystals, materials in which millions of molecules self-assemble into lattices so large (~ 100 nm) that they reflect visible light.
For years, two research groups at the University of Chicago’s Pritzker School of Molecular Engineering (PME) — led by Juan de Pablo, Liew Family Professor of Molecular Engineering, and Paul Nealey, Brady W. Dougan Professor of Molecular Engineering — have made key advances in studying blue phases on computers and then using those computational insights to assemble them perfectly in the lab.
In a Science Advances review paper, scientists and engineers from both groups survey the landscape and present the latest chemical, material, and theoretical developments in the field, with the hopes of spurring further interest in these next-generation materials.
“Through advances in computation, self-assembly, and chemistry researchers around the world have overcome significant obstacles that have been limiting the applicability of blue phases,” said Kushal Bagchi, a postdoctoral researcher and author on the paper. “We wanted to put those developments all in one place, to show people who work in technology and know nothing about blue phase liquid crystals that these materials hold promise for real-world applications.”
Creating materials from blue phase liquid crystals
To turn blue phase liquid crystals into materials, researchers have had to find ways to make them both thermally stable (since heating them up even one degree can destroy their properties) and macroscopically homogenous.
Last year, the de Pablo and Nealey groups turned blue phase liquid crystals into a single crystalline gel, taking a further step towards using them in novel applications. The final materials combined the interesting optical properties of the initial liquid and the mechanical robustness of the polymers we see all around us. This advance was only possible due to simultaneous developments in computation, chemistry, and self-assembly technology. In the review article, the authors take a deep dive into each of these developments separately and comment on exciting possibilities that emerge from combining advances in these different fields.
The ultimate goal, the researchers say, is to better understand and manipulate blue phase liquid crystals to create new kinds of technologies. While most color we see with our eyes is the result of light absorption, some structures — like butterfly wings or blue phases — produce color by reflecting light. These materials are called photonic crystals.
What makes blue phase-bases unique among photonic crystals is that they not only reflect light, but the wavelength at which they reflect can be tuned through applying stimuli. Blue-phase reflections can also be turned on and off. This single property is at the heart of the diverse range of technologies that blue phases could enable. Think of your kindle for instance, which is a reflective display. It produces images in black and white. If you used blue-phases whose color could be switched on and off, you could have colored kindles.
“You can also imagine wearable sensors for detecting humidity or a poisonous gas,” said Tadej Emeršič, a postdoctoral researcher and author on the paper. “It’s important to be able to improve properties of blue phases to use them for these technological applications, and our paper shows what is known and what is left to be done.”
Other authors on the paper include de Pablo, Nealey, and postdoctoral researcher José A. Martínez-González.
Citation: “Functional soft materials from blue phase liquid crystals,” Bagchi et al, Science Advances, July 26, 2023. DOI: 10.1126/sciadv.adh939.
Funding: Department of Energy