An aerogel is like dried Jello. That's how Kang P. Lee, founder of Aspen Aerogels Inc., likes to describe this light, airy material that has hundreds of possible uses as a heat, sound and shock insulator.
To make Jello, you mix a little powder with a lot of hot water and refrigerate it until it gels. If you could then remove the water, Lee said, you'd find that the gel is a network of tiny hair-like structures.
The trick to turning Jello into an aerogel is removing the water without collapsing that delicate scaffolding. The surface tension of water -- water's tendency to grip surfaces -- normally would tear down the tiny fibers as the water evaporated.
In a glass of water, surface tension is what causes the water's surface to curve upward slightly where it meets the glass, the water resisting the pull of gravity as it clings to the side.
A chemist, Samuel S. Kistler, figured out how to remove liquid from a gel and created the first aerogel in 1931, when he was at the College of the Pacific in Stockton, Calif. His solution was to increase the temperature and the pressure on the gel so that the liquid inside became "supercritical," a special state in which a material has some properties of a liquid and some of a gas. Significantly, a supercritical liquid, like a gas, has practically no surface tension.
Kistler couldn't easily make the process work with water, but found he could replace the water with alcohol and, once the alcohol became supercritical, allow it to escape.
This basic approach makes it possible to make aerogels out of just about anything that can be dissolved. Monsanto once produced aerogel granules made of silica for use as additives in cosmetics and toothpastes. More recently, NASA has used aerogels as insulation on the Mars Sojourner robot and as a medium to capture pure star dust, which was then returned to Earth for study.
Lee's Marlborough, Mass., firm specializes in silica aerogels -- "puffed up sand," as he calls it. He calls aerogels the original nanotechnology because the hair-like structures are only a nanometer -- a billionth of a meter -- in diameter and separated by only 20 nanometers.
The spacing is so tight, Lee said, that air molecules don't have much room to vibrate. And if an air molecule can't vibrate, it has trouble exciting other air molecules. And that means, he concluded, that heat and sound are not transmitted readily through an aerogel.
But silica aerogel can be fragile.
"You look at them, they want to break," Lee said, and that has limited their use.
His company has developed a method of incorporating silica aerogels in polyester batting, creating an aerogel blanket that is flexible and durable, while also preserving the insulating qualities of the aerogel.
Aspen provided 10 square feet of the aerogel blanket material to the Art Institute of Pittsburgh for use in insulating the insulin Will Cross will carry with him as he begins a 730-mile walk to the South Pole next month. Normally, the blankets are a pricey $45 per square foot.
"We're using Ph.D.s to make this," Lee said, explaining the high price for a product made of sand. The price should drop to about $3 per square foot when a larger production plant is opened. The blankets already are being used in some high-end winter clothing and, if the price comes down, could find their way into hundreds of products, including building insulation, he added.
