A close-up image of a millimeter-sized blue-phase liquid crystal during its formation stage. Image: Khoo Lab, Penn State.
A close-up image of a millimeter-sized blue-phase liquid crystal during its formation stage. Image: Khoo Lab, Penn State.

A new technique for changing the structure of liquid crystals could lead to the development of fast-responding liquid crystals suitable for next generation displays – 3D, augmented and virtual reality – and for advanced photonic applications such as mirrorless lasers, biosensors and fast/slow light generation. So says an international team of researchers from Penn State, the US Air Force Research Laboratory and the National Sun Yat-sen University in Taiwan.

"The liquid crystals we are working with are called blue-phase liquid crystals," said Iam Choon Khoo, professor of electrical engineering at Penn State and corresponding author of a paper on this work in Nature Materials. "The most important thing about this research is the fundamental understanding of what happens when you apply a field, which has led to the development of Repetitively-Applied Field technique. We believe that this method is almost a universal template that can be used for reconfiguring many similar types of liquid crystals and soft matter."

Blue-phase liquid crystals typically self-assemble into a cubic photonic-crystal structure, but the researchers believed that if they could get the liquid crystals to adopt other structures then these might possess novel properties. After nearly two years of experimentation, the researchers found that by applying an intermittent electrical field while allowing the system to relax between applications and dissipate accumulated heat, they could slowly coax the crystals into stable and field-free orthorhombic and tetragonal structures.

The resulting liquid crystals show a photonic band gap that can be tailored to anywhere within the visible spectrum, and also possess fast responses necessary for a variety of next-generation displays and advanced photonic applications. The addition of a polymer to the crystals stabilizes them over a wide temperature range, from freezing to nearly boiling point, whereas their pristine counterparts are stable over only a 5°C range. The polymer scaffold also speeds up the switching response.

The team is now applying the lessons learned in this study to create new crystal structures and orientations using the electric field from a laser source.

This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.