Pores of glass skin shrink from light

Anyone who’s suffered sunburn is well aware of the power of ultraviolet (UV) light.

Tubelike pores in an unhardened film shrink when exposed to ultraviolet light. Doshi, et al./Science

Researchers in New Mexico have found that they can use that power to fine-tune the properties of an unusual glass film they developed a few years ago. Riddled with pores only nanometers in diameter, the now-adjustable film may prove valuable as a sensor, filter, or optical material. With further development, it may even have the long-sought ability to extract oxygen or nitrogen directly from air, the scientists say. The standard gas-separation process requires expensive steps at cryogenic temperatures.

“If you could just have a filter that would let one gas through . . . that would be a big deal,” says research-team leader C. Jeffrey Brinker of Sandia National Laboratories in Albuquerque. In the Oct. 6 Science, Brinker, Dhaval A. Doshi of the University of New Mexico in Albuquerque, and their colleagues report using UV light to alter their film’s pore size, optical properties, and other features. UV irradiation is a new step in the team’s film-making process.

The initial step in that process yields 2-nm-diameter pores in the malleable film, which is made up of soaplike molecules, silica, and other materials. The researchers then expose some areas to UV light to induce chemical reactions that thicken the pores and reduce them by as much as 0.3 nm. Finally, the film is hardened into glass.

Doshi says the team is now trying to grow films with initial pore sizes around 0.5 nm that then can be shrunk with UV. Filtering oxygen from air by excluding nitrogen molecules requires 0.34 nm pores, a challenge that the researchers predict they can meet.

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