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White: No Longer The Most Reflective Colour

We all know that lighter colours reflect more light than darker ones, thus keeping the surface below cooler. Now, scientists have developed a new material, inspired by butterfly wings, that can produce vibrant colours while reflecting 100 percent of the light that hits them, to keep them cooler - up to a whopping 35 °C (63 °F) cooler in summer.


Pair of blue-winged butterflies
Credit: Wanlin Wang, Shenzhen University

A surface’s colour comes from the specific mix of wavelengths of light that it absorbs and reflects. Usually, the darker the colour the more light is absorbed. Now, however, scientists from Shenzhen University and Shanghai Jiao Tong University have successfully developed a film that doesn’t absorb any light at all, while still producing a vibrant colour.


This could help keep a building, vehicle or other object much cooler while also reducing the cost and environmental impact of air conditioning.


“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 Guo Ping Wang, lead researcher on the study. “Our cooling films could help advance energy sustainability and carbon neutrality.”


The key to the new film’s passive cooling abilities is its nanoscale structure. Intricate patterns on surfaces like butterfly wings or peacock feathers diffuse certain colours of light across a wide area, giving them the appearance of that colour. By cleverly tweaking and replicating this nanoscale structure, the team created films that appeared blue, yellow or colourless. They then tested samples on building roofs, cars, cloth and cell phones, during the day in both summer and winter, and measured their temperature. Sure enough, they found that the films remained substantially cooler than the surfaces they were placed on - more than 15 °C (27 °F) in winter and a whopping 35 °C (63 °F) cooler in summer.


The team is now investigating how to make the material less expensive and easier to manufacture so that it can be put to widespread beneficial use.


The research was published in the journal Optica.

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