Research at CMMPEMaterials — Blue phase liquid crystals

 

Liquid crystal blue phases are self assembled 3D cubic defect structures with the lattice periods of the order of the wavelength of visible light, which means that it reflects visible light of a particular colour. This makes them potentially useful for a variety of applications, from electrically switchable colour displays to light filters and lasers. But blue phases have a significant limitation: they exist over a very small range in temperature, typically no more than one degree Celsius at most.

The colour of the reflected light can be switched by applying an electric field to the material, and this could be used to produce three-colour (red-green-blue) pixels for full-colour displays. The materials may also be used in tuneable optical filters. Furthermore, because of the photonic band gap nature of the Blue Phase materials they may also readily be incorporated into 3D organic lasers. The electric field induced lattice distortion adds a new generation of continuously tuneable laser sources and opens up new perspectives for liquid crystal based photonics.

We have discovered a new class of blue-phase liquid crystals that remain stable over a very much wider range: from 16 to 60 degrees Celsius and possibly wider. 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 hundred nanometres, which give rise to vivid specular reflections controllable in external fields.

Further reading:

Liquid Crystal 'Blue Phases' with a Wide Temperature Range
Coles H.J. and Pivnenko M.N.
Nature 436, 997-1000, (2005)

Thermodynamically stable blue phases
F. Castles, S. M. Morris, E. M. Terentjev, H. J. Coles
Physical Review Letters, 104, 157801, (2010)
[PDF: copyright (2010) American Physical Society]

Want to know more about blue phases? Why not read:
CMMPE's introduction to liquid crystals

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