Paul Clem Randy Montoya
Sandia National Laboratories materials physicist Paul Clem holds a sample of nanoparticle coated glass. Thermochromic nanoparticles switch from infrared transparent to infrared reflective when they heat up, which will help keep office buildings, homes, and even cars cool.

Nanoparticle Film Turns Windows into Thermal Barriers

Thermochromic vanadium oxide could give single-pane windows the thermal insulation of double-pane windows.

Researchers at Sandia National Laboratories and New Mexico-based IR Dynamics have made a film coated with nano-sized particles that can reflect heat or infrared radiation. It could be used to keep commercial buildings and houses, cars, and even aircraft cool.

The small particles consist of vanadium dioxide, a thermochromic material, which means it changes its optical transmission characteristics with temperature. At cooler temperatures, it is transparent to infrared light. When it heats up, it becomes metallic and reflects infrared radiation without obstructing the view of visible light. This makes it different from electrochromic materials that change optical transmission in response to an electricity. Electrochromic glass, for example, is a growing sector of the window industry but is expensive and requiring infrastructure such as wires and switches.

The team worked on how to tune the switching temperature. For example, it might be best for car windows to start reflecting heat at 78° F, but another switching temperature might be better for other applications. By tweaking the “recipe” and adding tiny amounts of different metals, the team can now make nanoparticles that switch at any temperature ranging from −40° to 200°F.

The next engineering challenge for the team is figuring out how to economically make pounds of the nanoparticles—a necessary step toward manufacturing commercial products.

The first product the team hopes to get to market is a film to retrofit windows, something homeowners could apply to existing windows to reduce heating and cooling bills. Future applications could include incorporating the nanoparticles into new windows, architectural plastics (such as the kind used in the Water Cube of the 2008 Beijing Olympics), or high-performance athletic clothing.

The goal of the program is to make single-pane windows as energy efficient as double-pane windows. If every single-pane window in the U.S. was upgraded, it would save about 1.3% of all U.S. energy, or roughly the amount needed to power 32 million U.S. homes for a year. The researchers hope to have such a film on the market by late 2018.

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