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Liquid Crystal Shells Could Enable a New Type of Sensor

Photonics.com
May 2018
LUXEMBOURG, May 31, 2018 — Future uses for liquid crystals (LCs) could range far beyond flat screen TVs to include applications for autonomous driving, anticounterfeiting technology, and a new class of sensors.

Researchers from the University of Luxembourg, in collaboration with the New Jersey Institute of Technology, explored the properties of LC shells, looking for future application opportunities from an interdisciplinary standpoint.

‘Smart’ material could enable novel applications in autonomous driving, robotics, and sensor technology. Courtesy of University of Luxembourg.
‘Smart’ material could enable applications in autonomous driving, robotics, and sensor technology. Courtesy of University of Luxembourg.

Spherical shells of cholesteric liquid crystals (CLCs) reflect light omnidirectionally with specific polarization and wavelength, tunable from the UV to the IR range, and with complex patterns arising when many CLC shells are brought together. At only fractions of a millimeter in size, CLC shells can easily be applied to surfaces. Because they reflect light highly selectively, they can be arranged into patterns that can be read by machines. They can even be read by moving objects, since the shell pattern appears the same regardless of viewing angle.

“These patterns could be used to guide autonomous vehicles or to instruct robots when handling workpieces in a factory," said professor Jan Lagerwall. "This could become important especially in indoors applications where GPS devices don’t work.”

The micropatterns that emerge when the shells are combined are impossible to copy. Researchers believe these unique patterns could be used to create nonrepeatable identifiers that could be attached to valuable objects, such as art works or expensive pharmaceuticals. In combination with cryptographic tools, the patterns could be used to create a system that ensures that a buyer or user has an original product and not a counterfeit.

Along with analytical software, CLCs could be used as sensors — for example, as pressure sensors placed in the fingertips of robots, enabling tactile feeling, which is currently hard to achieve in robotic engineering. Another application could be fire exit signs that only become visible when the temperature exceeds a certain threshold. One advantage of these sensors, say the researchers, is the ability to passively react to external conditions without the need for electricity or batteries.

Advances in microfluidic techniques make it possible to produce CLC shells quickly and consistently. The shells can be rendered long-term stable by polymerization or polymer stabilization, or by templating into an inorganic replica. Additionally, the shells can be manufactured in a way that will allow them to change their structure when they are exposed to pressure, heat, some chemicals, and other external phenomena. 

Researchers believe that the most interesting options for CLC shells could arise when the conventional paradigm of applying the shells in flat geometries is set aside. Lagerwall said that further research into the ideas outlined in the article is required.

“Our hope is that the article can stimulate future research on liquid crystalline materials into new directions that are in line with the current societal developments,” he said.

The research was published in Advanced Materials (doi:10.1002/adma.201707382).

Research & TechnologyEuropeeducationDisplayslight sourcesmaterialsSensors & DetectorsindustrialConsumersecurityliquid crystalscholesteric liquid crystals

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