On a hot summer day, white clothes seem cooler than other colors because they reflect rather than absorb sunlight. Other colors, such as blue or black, are subjected to a heating effect, as they absorb light. To circumvent this heating effect in color cooling films, the researchers drew inspiration from nanostructures in the wings of the morpho butterfly, which have a rich, bright blue color, but practically do not heat up.
Scientists at Shenzhen University in China have developed special reflective films that will help cool objects in the open in the heat. New films that do not absorb light can be used outside buildings, vehicles and equipment to reduce the energy needed to cool them.
"In buildings, a large amount of energy is used for cooling and ventilation, and the operation of an air conditioner in an electric car can reduce the mileage by more than half," comments Wanlin Wang, head of the research group. "Our cooling films can contribute to energy efficiency and carbon neutrality."
In the journal Optica Publishing Group, dedicated to high-performance research, scientists show that the films they have developed reduce the temperature of colored objects. To test the new technology, the researchers created blue, yellow and colorless films, which they placed outdoors on surfaces such as roofs, cars, fabric and mobile phones, from 9 a.m. to 4 p.m.
Using thermocouple sensors and infrared cameras to measure temperature, they found that cooling films on average have a temperature 2°C lower than the environment and can significantly reduce the temperature of the surfaces on which they are placed. At the same time, the difference in cooling performance depended on the time of the objects' stay on the street, as well as the type of surface with which the film was compared.
In particular, it turned out that, for example, the blue version of the film was about 26 °C colder than the traditional car paint of the same shade on a car parked outside all day.
Now the films are created with a thin layer of silver, but in the future it is planned to create an alternative made of aluminum, which will reduce the cost of production.
"With our new films, it is possible to achieve excellent cooling performance regardless of the desired color, saturation or brightness," Wang said. "They could even be used on textiles to create clothes of any color that are comfortable at high temperatures."
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