Researchers from University of Rochester have created a hard plastic membrane, full of tiny holes, that can go between being permeable and impermeable to gas by shining light of different wavelengths. The holes in the membrane are filled with liquid crystals and a light reactive dye. When blue light is shined onto the dye, it lines up and the liquid crystals follow suit, creating a passage. When ultraviolet light is applied, the dye crinkles and so do the liquid crystals, blocking the hole. We can imagine drug dispensing devices that are stuck on or under the skin that can be easily switched on and off using a pocket light.
Creating the membrane is a multi-step process. First, a circular hard plastic chip is bombarded with a beam of neutrons to make the tiny, evenly spaced holes that are about one-hundredth of a millimeter in diameter. The chip is then dipped in a solution of liquid crystals and dye, and the mixture fills the holes through capillary action. The final product is spun in a centrifuge to remove the excess liquid crystals from the surface.
Controlling a membrane’s permeability with light is preferable to controlling it with heat or electricity – two readily used alternative methods – for several reasons, Glowacki [Eric Glowacki, a graduate student at the University’s Laboratory for Laser Energetics] said. 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 much smaller, simpler setups.
Another advantage is that the color of the light illuminating the membrane can be changed precisely and almost instantaneously. Other methods, like heating and cooling, take a relatively long time and repeated heating and cooling can damage the membrane.
Also, light does not have the potential to ignite a gas, which could be a crucial benefit when working with hydrocarbons or other flammable gases. Lastly, the amount of light energy needed to switch the membrane on and off is miniscule.
Press release: Purple Light Means Go, Ultraviolet Light Means Stop …
(hat tip: io9)
