Electrifying boon for storage devices
doi:10.1038/nindia.2008.147 Published online 19 March 2008
Researchers have devised a new method to transform the shape of a liquid crystal, a finding that will have applications in optical data storage devices such as CDs and DVDs. The researchers have used electric field as a tool to accelerate the shape transformation of the crystal, which in turn could help devices work faster.
Photonics, in which light can be controlled by light as a stimulus, is a field of growing interest. Liquid crystals show birefringence (double refraction) when light passes through them. This property has applications in optical data storage.
The researchers took a form (E) of azobenzene and irradiated it with ultraviolet rays. The rod-like molecular form E gave rise to a bent form Z. E and Z are structurally different forms of the same molecule and called isomers. In visible light and even in darkness, Z can change into E. The Z to E transformation in darkness is called thermal back relaxation (TBR). But, both processes are slow. The time taken for such transformation has significance in device applications.
So, the researchers applied a low-frequency electric field, which significantly accelerated the transformation of Z to E. The transition from Z to E, which required 2000 seconds, occurs in less than 100 seconds when DC voltage (20V) was applied.
TBR is time-taking and could range from tens of minutes to days limiting the speed of the device and its optical response. "The newness in this work is that electric field speeds up the transformation of Z to E at least two orders of magnitude faster," says lead researcher S. Krishna Prasad from the Center for Liquid Crystal Research, Bangalore, India.
- Prasad, K. S. et al. Electric-Field-Assisted Acceleration of the Photostimulated Nematic-Isotropic Transition. Adv. Mater. doi: 10.1002/adma.200701393 (2008)