A transparent aerogel made from readily-available beer waste could insulate existing windows and more

Qingkun Liu, a posdoctoral researcher in physics, lifts up a petri dish holding samples of a new aerogel. (Credit: CU Boulder)

Can a new type of transparent gel, made from readily-available beer waste, help engineers build greenhouses on Mars?

CU Boulder physicists have developed an insulating gel that they say could coat the windows of habitats in space, allowing the settlers inside to trap and store energy from the sun—much like a greenhouse stays warm during the winter. And unlike similar products on the market, the material is mostly see-through.

“Transparency is an enabling feature because you can use this gel in windows, and you could use it in extraterrestrial habitats,” said Ivan Smalyukh, a professor in the Department of Physics. “You could harvest sunlight through that thermally insulating material and store the energy inside, protecting yourself from those big oscillations in temperature that you have on Mars or on the moon.”

The defining feature of aerogels, as their name suggests, is air, Smalyukh explained. By weight, these thin films are 90 percent gas. Engineers achieve this feather weight by generating crisscrossing patterns of solid material that trap air inside billions of tiny pores, similar to the bubbles in bubble wrap. It’s that trapping capacity that makes them such good insulators.

“You create a very tortuous network of these nanoparticles that link together in the aerogel, preventing the heat from going through,” Smalyukh said.

Beer to windows

That same network, however, tends to scatter light, making aerogels look cloudy and explaining why some engineers call them “frozen smoke.”

To make a more translucent gel, Smalyukh and his colleagues begin with the common plant sugar cellulose. By carefully controlling how cellulose molecules link up, the team is able to orient them into a lattice-like pattern.

That pattern is so uniform, he said, that it allows light to pass through unbothered, giving the gel its transparent appearance.

Problem solved. In order to find a ready supply of cellulose for their space-age material, the researchers turned to a substance with humble beginnings: a refreshing IPA.

Unused beer wort, or waste liquid produced during the brewing process, can make cellulose when scientists add in specialized bacteria. The researchers began driving to breweries across the Boulder area to collect tubs of unwanted liquid from beer-makers.

“So not only are we recycling and saving this valuable material from entering the landfill, but we’re also producing this raw material cheaply,” said Andrew Hess, a Ph.D. student in physics at CU Boulder.

Currently, it takes the team about two weeks to culture the cellulose, but the rest of the process of making the aerogel moves quickly. The final product of the team’s efforts is a thin, flexible film that is roughly 100 times lighter than glass. This gel is so resistant to heat that you could put a strip of it on your hand and light a fire on top—without feeling a thing.

Mars to Antarctica