14 DAY TRIAL // Light-controlled membranes represent a concept that is so advanced it hasn't even made its way into science-fiction literature. Nevertheless, they are now a reality, thanks to a study conducted by investigators at the University of Rochester. The group managed to create membranes which allow or prevent gas from passing through based on what kind of light is shone on their surface.
If purple light is dominant, then gas molecules are allowed to pass. Conversely, when ultraviolet (UV) light is shone on the membrane, the gas is prevented from passing through. The investigators behind the accomplishment, based at the university's Laboratory for Laser Energetics (LLE), say that this is the first time such a device has been produced. The membrane itself was invented by graduate student Eric Glowacki, who collaborated closely with advisor Kenneth Marshall, a professor at Rochester.
The membrane itself is basically a hard sheet of plastic. Its surface is riddled with very small holes, each of which contains a special type of liquid crystals, and a particular brand of dye. When purple light is shone on the membrane, the molecules inside the dye straighten out, triggering a motion among the liquid crystals that makes the latter fall into a straight line. Conversely, when UV light touches the dye molecule, they bend until they become semi-circular, and scatter the liquid crystals into random configurations. The membrane then becomes impenetrable for the gas molecules.
Until now, gas membranes were controlled via either heat or electricity, but investigators say that using light is the best approach. One of the main advantages in using photons is the fact that the control source can be located away from the membrane, with no direct contact. When electricity is used, wires have to be attached to the membranes, and this limits their uses at time. Details on the new control method were presented yesterday, August 1, at the annual conference of the International Society for Optics and Photonics (SPIE), which was held in San Diego.