‘Chameleon’ Coating Adjusts to Outside Temps

THURSDAY, SEPTEMBER 21, 2023


A research team has reportedly developed a new energy-efficient coating that mimics the qualities of a desert chameleon to keep buildings cool in the summer and warm in the winter.

Fuqiang Wang and colleagues were inspired by the Namanqua chameleon, which changes its color to regulate its body temperature in southwestern Africa. In hot conditions, the animal turns light grey to reflect the sunlight; on the other hand, a dark brown color is adapted to absorb heat in cooler temps.

According to a release from the American Chemical Society, Wang’s team wanted to develop a color-shifting coating that mimics these qualities, switching between “modes” to create more energy-efficient buildings.

Researchers reportedly mixed thermochromic microcapsules, specialized microparticles and binders to form a suspension and make the coating. Then, they sprayed or brushed it onto a metal surface.

When heated to 68 degrees Fahrenheit, the surface began to change from dark to light grey. Increased to 86 F, the light-colored film also reflected up to 93% of solar radiation. The team explained that even when heated above 175 F for an entire day, the material showed no signs of damage.

The coating was then tested alongside three conventional coatings, including regular white paint, a passive radiative cooling paint and blue steel tiles, in outdoor tests on miniature, doghouse-sized buildings.

Testing reportedly found that:

  • In winter, the new coating was slightly warmer than the passive radiative cooling system, though both maintained similar temperatures in warmer conditions;
  • In summer, the new coating was significantly cooler than the white paint and steel tiles; and
  • During spring and fall, the new coating was the only system that could adapt to the widely fluctuating temperatures changes, switching from heating to cooling throughout the day.

The researchers explain that this system could save “a considerable amount of energy for regions that experience multiple seasons, while still being inexpensive and easy to manufacture.”

The results of the study were recently published in the journal Nano Letters. Funding was provided by the National Natural Science Foundation of China, the Taishan Scholars of Shandong Province, the Royal Society and the China Scholarship Council.

Recent Energy Efficient Coatings

In March, scientists from Cambridge University unveiled a new plant-based coating that gets cooler when exposed to sunlight. Available in a variety of textures and iridescent colors, the material reportedly aims to keep buildings, cars and other structures cool without external power.

For the research, the team reportedly layered colorful cellulose nanocrystal materials with a white-colored material made from ethyl cellulose, producing a colorful bi-layered PDRC film. They made films with vibrant blue, green and red colors that, when placed under sunlight, were an average of nearly 40 degrees Fahrenheit cooler than the surrounding air. 

The researchers said that a square meter of the film generated over 120 watts of cooling power. Since CN films were brittle and the ethyl cellulose layer had to be plasma-treated to get good adhesion, the resulting films are described as robust and can be prepared several meters at a time in a standard manufacturing line.

Last month, a new kind of paint from Stanford University was reported to keep buildings cooler in the summer and warmer in the winter, reducing energy use, costs and greenhouse gas emissions.

According to the researchers, while heating and cooling accounts for about 13% of global energy use and about 11% of GHG emissions, the new colorful paints were able to reduce the energy used by approximately 36% in artificial cool conditions and almost 21% in artificial warm conditions.

Additionally, in simulations of a typical mid-rise apartment building with the new paint on the exterior walls and roofs, total energy use declined 7.4% over a year.  Standford explained that current low-emissivity paints typically have a metallic silver or gray color, limiting use. However, the new paint has two layers applied separately, including:

  • An infrared reflective bottom layer using aluminum flakes; and
  • An ultrathin, infrared transparent upper layer using inorganic nanoparticles that comes in a wide range of colors.

The paint can reportedly be applied to exterior walls and roofs, allowing most of the sun’s infrared light to pass through the colored layer of the paint, reflect off the lower layer and pass back out as light rather than be absorbed as heat. Alternatively, to keep heat inside, the paints would be applied to interior walls where it would reflect the infrared waves.

   

Tagged categories: Asia Pacific; Biomimicry; Coating Materials - Commercial; Coatings; Coatings Technology; Coatings Technology; Coatings technology; EMEA (Europe, Middle East and Africa); Energy efficiency; Green coatings; Latin America; North America; Program/Project Management; Research and development; Temperature; Z-Continents

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