Building Insulation Clear View, Less Heat Loss: Researchers Develop Transparent Window Insulation

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Windows are among the biggest weak points in energy-efficient buildings. A new transparent insulation material developed at the University of Colorado Boulder could change that — combining near-perfect clarity with remarkable heat-blocking performance.

Physicists at the University of Colorado Boulder have designed a new material for insulating windows that could improve the energy efficiency of buildings worldwide — and it works a bit like a high-tech version of Bubble Wrap. The team’s material, called Mesoporous Optically Clear Heat Insulator, or Mochi, comes in large slabs or thin sheets that can be applied to the inside of any window. So far, the team only makes the material in the lab, and it’s not available for consumers. But the researchers say Mochi is long-lasting and is almost completely transparent. That means it won’t disrupt your view, unlike many insulating materials on the market today.

“To block heat exchange, you can put a lot of insulation in your walls, but windows need to be transparent,” said Ivan Smalyukh, senior author of the study and a professor of physics at CU Boulder. “Finding insulators that are transparent is really challenging.”

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Buildings, from single-family homes to office skyscrapers, consume about 40 % of all energy generated worldwide. They also leak, losing heat to the outdoors on cold days and absorbing heat when the temperature rises.

Smalyukh and his colleagues aim to slow down that exchange. The group’s Mochi material is a silicone gel with a twist: The gel traps air through a network of tiny pores that are many times thinner than the width of a human hair. Those tiny air bubbles are so good at blocking heat that you can use a Mochi sheet just 5 millimeters thick to hold a flame in the palm of your hand.

“No matter what the temperatures are outside, we want people to be able to have comfortable temperatures inside without having to waste energy,” said Smalyukh, a fellow at the Renewable And Sustainable Energy Institute (Rasei) at CU Boulder.

Bubble Magic

Smalyukh said the secret to Mochi comes down to precisely controlling those pockets of air. The team’s new invention is similar to aerogels, a class of insulating material that is in widespread use today. (Nasa uses aerogels inside its Mars rovers to keep electronics warm).

Like Mochi, aerogels trap countless pockets of air. But those bubbles tend to be distributed randomly throughout aerogels and often reflect light rather than let it pass through. As a result, these materials often look cloudy, which is why they’re sometimes called “frozen smoke.” In the new research, Smalyukh and his colleagues wanted to take a different approach to insulation.

To make Mochi, the group mixes a special type of molecule known as surfactants into a liquid solution. These molecules natural clump together to form thin threads in a process not unlike how oil and vinegar separate in salad dressing. Next, molecules of silicone in the same solution begin to stick to the outside of those threads.

Through a series of steps, the researchers then replace the clumps of detergent molecules with air. That leaves silicone surrounding a network of incredibly small pipes filled with air, which Smalyukh compares to a “plumber’s nightmare.”

In all, air makes up more than 90 % of the volume of the Mochi material.

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Trapping Heat

Smalyukh said that heat passes through a gas in a process something like a game of pool: Heat energizes molecules and atoms in the gas, which then bang into other molecules and atoms, transferring the energy. The bubbles in Mochi material are so small, however, that the gases inside can’t bang into each other, effectively keeping heat from flowing through. “The molecules don’t have a chance to collide freely with each other and exchange energy,” Smalyukh said. “Instead, they bump into the walls of the pores.” At the same time, the Mochi material only reflects about .2 % of incoming light.

The researchers see a lot of uses for this clear-but-insulating material. Engineers could design a device that uses Mochi to trap the heat from sunlight, converting it into cheap and sustainable energy. “Even when it’s a somewhat cloudy day, you could still harness a lot of energy and then use it to heat your water and your building interior,” Smalyukh said.

You probably won’t see these products on the market soon. Currently, the team relies on a time-intensive process to produce Mochi in the lab. But Smalyukh believes the manufacturing process can be streamlined. The ingredients his team uses to make Mochi are also relatively inexpensive, which the physicist said bodes well for turning this material into a commercial product.

For now, the future for Mochi, like the view through a window coated in this insulating material, looks bright.

Original Article: Mesoporous optically clear heat insulators for sustainable building envelopes; Science; DOI:10.1126/science.adx5568

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