On a scorching summer day, wearing white clothing can make anyone feel cooler than donning darker colors because white reflects sunlight instead of absorbing it. However, researchers have recently developed a groundbreaking solution inspired by the nanostructures found in butterfly wings to create cooling films that maintain vibrant colors while reducing heat absorption. These films have the potential to revolutionize the energy consumption of buildings, vehicles, and equipment, advancing energy sustainability, and carbon neutrality.
The Science behind the Films
The cooling films developed by a team of researchers from Shenzhen University in China take inspiration from the nanostructures present in Morpho butterfly wings. Unlike traditional colored films that absorb sunlight and generate heat, these innovative films do not absorb any light. By mimicking the nanostructures found in butterfly wings, the films achieve vibrant colors without the heating effect of sunlight absorption.
In their study published in Optica, the researchers demonstrate that their newly developed films can lower the temperature of colored objects to approximately 2°C below the ambient temperature. Additionally, when compared to traditional blue car paint, the blue version of the films remained approximately 26°C cooler when exposed to sunlight throughout the day. This remarkable cooling effect translates into significant annual energy savings of approximately 1,377 MJ/m2 per year.
The potential applications for these cooling films are vast. They can be used on the exteriors of buildings, vehicles, and equipment to reduce the energy required for cooling while preserving their vivid color properties. Moreover, the films can be implemented in textiles, allowing the creation of clothes in any desired color that offer comfort in hot temperatures. This advancement could revolutionize the fashion industry and enhance the comfort of individuals in warm climates.
The Morpho-inspired nanofilms are composed of a multilayer material consisting of titanium dioxide and aluminum dioxide placed on a silver layer that reflects all light, preventing the absorption of solar radiation and the associated heating. The color of the films is determined by the components within the multilayered structure that reflect light. For example, to create blue, the multilayer material reflects yellow light within a specific range of angles, while the disordered structure of the film diffuses blue light across a broader area.
While passive photonic thermal management has previously been achieved, it has predominantly been limited to white or clear objects due to challenges in maintaining a wide viewing angle and high color saturation. The breakthrough achieved by the researchers lies in their ability to extend this cooling method to colorful objects while preserving their color performance. The blue film, for instance, retains its characteristic blue hue across a wide range of viewing angles and remains cool because it reflects all light. Moreover, the optimized structure of the film enables high saturation and brightness.
Testing and Future Developments
To validate the effectiveness of the new technology, the researchers conducted outdoor testing by placing blue, yellow, and colorless films on various surfaces such as roofs, cars, cloth, and cell phones. The results proved the remarkable cooling capabilities of the films, with temperatures more than 15°C lower than the surfaces they were applied to in winter and approximately 35°C cooler in the summer. The researchers suggest that replacing the silver film with an aluminum film could reduce the manufacturing cost and facilitate scalable fabrication methods.
The development of nanostructured cooling films presents an exciting solution to energy sustainability and carbon neutrality. By leveraging the inspiration from butterfly wings, these films provide effective cooling while maintaining vibrant colors. The potential applications of these films span across various industries, from architecture to fashion, offering immense opportunities for energy-efficient cooling. With further research and optimization, these films hold the potential to transform our energy consumption and contribute to a more sustainable future.
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