Posted in | Nanomaterials | Nanoanalysis

Car and House Windows that Stay Warm in Winter and Cool in Summer

A car sitting in the sun on a Summer’s day is scorching and this indeed is a fact that has been acknowledged almost throughout the whole world. However, this truth could soon be challenged by a collaboration between Sandia National Laboratories and Santa Fe, New Mexico-based IR Dynamics.

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 to keep office buildings, homes and even cars cool. (Photo by Randy Montoya)

Together they are turning nano-size particles reflect infrared radiation, or heat, into window films for houses, offices and also cars.

With the help of a New Mexico Small Business Assistance, (NMSBA), grant, the partnership commenced in 2013. Paul Clem, a Sandia Materials Physicist, was analyzing studying films 50 times thinner than a strand of human hair that switch from insulators that block electricity to metals conducting heat, based on the temperature. Clem was exploring their potential use in electronics when he encountered William Kurtz, who led a company developing energy-efficient aerogel-insulated windows and skylights.  Both of them met in a tech park in Santa Fe and began to talk about the requirement for windows capable of automatically allowing heat in during winter months and also keeping it out in the summer months.

Some materials are considered to be reflective, like aluminum foil, and reflect heat and light. Other materials are usually transparent to light, like plastic and glass. Based on their temperature, it is possible for a few rare materials to be both. One such material is vanadium dioxide.

Vanadium dioxide is in fact thermochromic, and is capable of changing its optical transmission with temperature. It is transparent to infrared light at cooler temperatures. When heated, it becomes metallic and reflects infrared, or IR, radiation without hindering the view of visible light. The company name IR Dynamics was obtained as a result of this dynamic switch between IR transparent and IR reflective.

Vanadium dioxide materials switch because of temperature instead of from applying electricity like electrochromic materials. Electrochromic glass is considered to be a growing sector of the window industry but requires infrastructure such as switches and wires, despite being expensive. Thermochromic materials are interesting commercially and scientifically as they switch due to the temperature of the environment.

Tunable and reflective nanoparticles

Several years were spent by a team of Researchers including Clem in order to develop easy-to-apply polymer films with thermochromic nanoparticles and they were supported by NMSBA grants and a Cooperative Research and Development Agreement (CRADA).

Nelson Bell, a Sandia Materials Chemist, was initially responsible for designing and implementing a multistage process to produce nanoparticles. He also established the best way to disperse the nanoparticles in a spray-paint-like mixture, which resulted in Bell calling himself a Paint Chemist.

According to Kurtz and Clem, the greatest challenge was to discover how to make pounds of the nanoparticles needed to develop commercial products.

The team also focused on how to tune the switching temperature. For instance, it could be best for car windows to start reflecting heat at 78 oF but another temperature might also be better for several other applications.  The team succeeded in making nanoparticles capable of switching at any temperature from 200 oF to -40 oF by modifying small amounts of varied metals.

Raegan Johnson, a Sandia Materials Scientist, was responsible for characterizing these “batches” of nanoparticles in order to make sure they had the correct properties. She determined the infrared absorbance, physical structure and chemical structure of the nanoparticles by using high-end equipment, such as a transmission electron microscope, X-ray diffraction instrumentation and a Fourier transform infrared spectrometer.

“A startup the size of IR Dynamics can’t afford to purchase the diagnostic equipment that is available through Sandia Labs. Through the NMSBA and CRADA programs we are able to use those resources to develop the technology,” said Kurtz. “It is important for small technology companies like ours to be able to partner with the national laboratories. I think that it is part of what keeps us competitive as a nation with the rest of the world.”

Nanoparticles for retrofitting windows

A film to retrofit windows is the first product Kurtz hopes to get to market. This is something homeowners could apply to their existing windows in order to reduce their cooling and heating bills. Future applications comprise of incorporating the nanoparticles into new windows, and then adding them to architectural plastics, such as the type used in high-performance athletic clothing, or the Water Cube of the 2008 Beijing Olympics.

IR Dynamics received a $1.95 million grant from the Department of Energy’s Advanced Research Project Agency-Energy SHIELD program, in 2016, in order to bridge “the valley of death” — a problematic period for startups before they develop a profitable product — and make retrofit window films a reality. This program aimed at making single-pane windows as energy efficient as double-pane windows. Upgrading a single-pane window in the U.S. will help save almost 1.3% of all U.S. energy, or approximately the amount required for powering 32 million U.S. homes each year.

Several of the other projects funded via the program focus on decreasing heat loss, which is a vital concern nationwide. However, in certain areas of the U.S., cooling needs more electricity than heating, which allows making windows capable of reducing the costs from both real winners.

Kurtz is hoping to commercialize these retrofit window films by late 2018. Several patents have been filed by the company. IR Dynamics is also collaborating with a top company in the high-performance fabric industry and a leading corporation in the window-film and structural plastics industries.

Usually the things we do are in technical journals or are presented at specialized conferences. It’s rewarding to see things go from idea to a commercial product. For this company we can point to five new jobs that all started from the first NMSBA grant. Seeing new companies start up and grow knowing you’ve given them a technical boost is satisfying.

Paul Clem, Materials Physicist, Sandia National Laboratories

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