New Nanofilms to Reduce Energy Usage

Researchers from Shenzhen University in China have developed new films for building exteriors, vehicles and equipment that don’t absorb light reducing the amount of cooling energy needed.
 
Research was led by Wanllin Wang and have been published in the journal Optica. Reportedly the film was inspired by the nanostructures in butterfly wings and can lower the temperature of colorful objects to about two degrees below ambient temperatures. 
 
“In buildings, large amounts of energy are used for cooling and ventilation, and running the air conditioner in electric cars reduce the driving range by more than half,” said Guo Ping Wang from Shenzhen University. “Our cooling films could help advance energy sustainability and carbon neutrality. 
 
Scientists say that the design from the cooling nanofilm replicates Morpho butterflies. The research explains that a car painted blue appears blue because it absorbs yellow light and heat to reflect blue light. The Morpho butterfly appears blue due to the nanostructure of their wings.
 
Reportedly the nanofilms are produced by placing a disordered material, or rough frosted glass under a multilayer material made of titanium dioxide and aluminum dioxide. Then the structure is placed in a silver layer that reflects all light, consequently preventing the absorption of solar radiation and heat.
 
Thanks to the layered structure we developed, we are able to extend the passive cooling method from colorless objects to colorful ones while preserving color performance,” said Guo Ping 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 film’s color is determined by how components in the multilayered structure reflect light. To create blue the multilayer material reflects yellow light in very narrow range angles while the disordered structure diffuses the blue light across a large area.
 
The research team created colorless, blue, and yellow films, which were placed outdoors at Shenzhen University on roofs, cars, cell phones, and cloth throughout the day in both summer and winter weather.
 
Thermocouple sensors and infrared camera were used to measure temperatures. Scientists found that the films were about 15 C cooler than untreated surfaces in the winter, and in the summer untreated surfaces were about 35 C cooler. 
 
Researchers note that replacing the silver film with an aluminum film would make the films more manufacturable by scalable fabrication method. The team also plans to study other properties such as chemical and mechanical robustness.