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September 15, 2010

In Research

Purple light means go, ultraviolet light means stop

student holding membrane
Graduate student Eric Glowacki holds the membrane that he and Kenneth Marshall developed at the Laboratory for Laser Energetics. The membrane changes permeability with different colors of light.

A new membrane developed at the Laboratory for Laser Energetics blocks gas from flowing through it when one color of light is shined on its surface and permits gas to flow through when another color of light is used. It is the first time that scientists have developed a membrane that can be controlled in this way by light.

Eric Glowacki, a graduate student at the University’s Laboratory for Laser Energetics, and Kenneth Marshall, his advisor, invented the membrane. Marshall presented their findings last month at the annual conference of the International Society for Optics and Photonics in San Diego.

The membrane is a piece of hard plastic riddled with tiny holes that are filled with liquid crystals and a dye. When purple light illuminates the surface of the membrane, the dye molecules straighten out, and the liquid crystals fall into line, which allows gas to easily flow through the holes. But when ultraviolet light illuminates the surface, the dye molecules bend into a banana shape and the liquid crystals scatter into random orientations, clogging the tunnel and blocking gas from penetrating.

Controlling a membrane’s permeability with light is preferable to controlling it with heat or electricity for several reasons, Glowacki says. For starters, light can operate remotely. Instead of attaching electrical lines to the membrane, a lamp or a laser can be directed at the membrane from a distance. This could allow engineers to make smaller, simpler setups. Another advantage is that the color of the light illuminating the membrane can be changed precisely and almost instantaneously.

The membrane could be useful in controlled drug delivery and industrial processing tasks that require the ability to turn the flow of gas on and off as well as in research applications.

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