New butterfly-inspired films have powerful cooling effects

They can lower the temperature of colorful objects to about 35 °F below the ambient temperature. 
Loukia Papadopoulos
Butterfly wings.jpg
Butterfly wings.


Scientists have drawn inspiration from the nanostructures in butterfly wings to circumvent the heating effect in colored cooling films often experienced during hotter periods.

This is according to a press release by the journal OPTICA published on Thursday. 

The resulting films don’t absorb any light, making them ideal candidates for use on the outside of buildings, vehicles, and equipment in order to reduce the energy needed for cooling while preserving vivid color properties.

Advancing energy sustainability

“In buildings, large amounts of energy are used for cooling and ventilation, and running the air conditioner in electric cars can reduce the driving range by more than half,” said research team leader Wanlin Wang from Shenzhen University in China. “Our cooling films could help advance energy sustainability and carbon neutrality.”

In the new research, the scientists show that the newly-developed films lower the temperature of colorful objects to about 35 Fahrenheit (2 Celsius) below the ambient temperature. 

“With our new films, excellent cooling performance can be achieved, no matter the desired color, saturation or brightness,” said Wang. “They could even be used on textiles to create clothes of any color that are comfortable in hot temperatures.”

The researchers were inspired by morpho butterflies which produce a highly saturated blue color based on the nanostructure of their wings. They thus engineered a design for nanofilms that mimics these structures to produce vibrant colors that don’t absorb light like traditional paint.

Passive photonic thermal management has been attempted before, but thus far, it has only been used with white or clear objects because it is difficult to maintain a wide viewing angle and high color saturation.

Passive cooling method

“Thanks to the layered structure we developed, we were able to extend the passive cooling method from colorless objects to colorful ones while preserving color performance,” said Wang. “In other words, our blue film looks blue across a large range of viewing angles and doesn’t heat up because it reflects all the light. In addition, high saturation and brightness can be achieved by optimizing the structure.”

The new technology was tested through the creation of blue, yellow, and colorless films, which the researchers placed outdoors at Shenzhen University, on surfaces such as roofs, cars, cloth, and cell phones, from 9 a.m. to 4 p.m. in both winter and summer. The results indicated that the cooling films were more than 59 degrees Fahrenheit (15 Celsius) cooler than the surfaces they were placed on in the winter and 95 degrees Fahrenheit (35 Celsius) cooler in the summer.  

For the next steps, the researchers plan to study and optimize other properties of the films, such as mechanical and chemical robustness.

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