Liquid crystal switching reaches new speeds

Science : Liquid crystals are freely moving rod-like molecules that are oriented in the same direction along their long axis. Their shared alignment causes polarized light to travel through the material at different rates depending on its angle with respect to the crystal alignment. Controlling the alignment of individual liquid crystals—by turning an electric field on and off—is how images are created on LCD screens. Currently, turning the liquid crystals “on” takes just nanoseconds because of the force applied by the electric field, but turning them off takes longer—milliseconds—because, without the electric field, thermal energy pushes the crystals out of alignment, but doesn’t apply nearly as much force. A new technique, developed by Oleg Lavrentovich of Kent State University in Ohio and his colleagues, reduces the turn-off time to nanoseconds as well. They used a normal LCD screen with a liquid crystal called CCN-47, which has plank-shaped molecules instead of cylindrical ones. Because of their shape, the electric field caused the molecules to align on a secondary axis such that the wider sides all faced the same direction. This axis of rotation is more sensitive to thermal energy than is the longer axis, so turning off the electric field meant that the alignment of the molecules was lost more quickly than is the case for traditional liquid crystals. The resulting on–off process is much faster than is needed for current LCDs, however, so applications aren’t immediately apparent.