Researchers at the University’s Department of Engineering have discovered a class of blue-phase liquid crystals that remain stable over a wide range: from 16 to 60 degrees.

Liquid-crystal 'blue phases' can be just about any colour in the rainbow. This makes them potentially useful for all sorts of applications, from electrically switchable colour displays to light filters and lasers. However, blue phases have a significant limitation as they exist over a very small range in temperature, typically no more than two degrees Celsius at most.

In this week’s scientific journal Nature, Professor Harry Coles and Dr Mikhail Pivnenko from the Photonics Group of the Engineering Department report a solution to this instability.

The researchers show that their ultrastable blue phases could find some useful applications in optical technology. Typically, liquid crystals are made from rod-like molecules that line up in at least one direction while remaining mobile and disorderly in the others. In blue phases, this alignment of molecules takes a complicated form: the molecules assemble into cylindrically shaped arrays in which the direction of alignment twists in a helix, while the helices themselves criss-cross in three dimensions. The structure repeats regularly every several 100 nanometres, which means that it reflects visible light of a particular colour. The new blue phases are made from molecules in which two stiff, rod-like segments are linked by a flexible chain.

“It is this unusual structure that makes the blue phase so stable,” said Professor Coles.

“We have shown that the colour of the reflected light can be switched by applying an electric field to the material, and that this could be used to produce three-colour (red-green-blue) pixels for full-colour displays.”

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.