Forget the chaos theory, here’s how one group of researchers are planning to keep cars cool with butterfly wing-inspired reflective films.
A thin, multi-layered film based on the structure of vibrant blue butterfly wings could help vehicles reduce energy used for cooling when applied to their exterior. Designed and developed by a group of researchers from Shenzhen University and Shanghai Jiao Tong University, the novel film is inspired by Morpho butterfly wings which are covered in nanostructures that bounce and bend incoming light to produce a vivid blue colour.
Looking to replicate this effect for the purpose of cooling cars, in particular electric vehicles (EVs), the researchers designed a thin film to act in a similar way to energy-saving reflective paints currently on the automotive market.
MULTI-LAYERED MATERIALS
The colours of objects originate from the reflection of light in certain directions and the absorption of undesired light, which produces heat. Extensive efforts are made to cool colourful objects to reduce their energy consumption, however it remains challenging to achieve this while preserving an object’s excellent colour properties. Recently, colourless objects have been cooled using methods such as increasing solar reflection and increasing mid-IR radiation, and while efforts have been made to extend this passive cooling method from colourless to colourful objects, this has not been effective for some colours, like highly saturated blue and green.
To overcome these challenges, the researchers embarked upon designing a multilayer, disordered material structure capable of cooling colourful objects inspired by Morphos butterfly wings.
The researchers designed the film to be just a few micrometres thick and made up of three distinct layers: the top is made from a compound of titanium, silicon and oxygen, while the other two consist of a special frosted glass and a thin silver mirror. The glass layer has numerous tiny structures to give it a frosted look and mimic the appearance of the Morphos wings.
TESTING THE COOLING CAPABILITIES
The group designed film samples in several colours including red, green and blue, then exposed them to sunlight for around seven hours while monitoring their temperature. All the samples stayed about 2°C cooler than the air around them. However, their cooling power became more evident when the researchers attached one sample to a car and compared it to a patch of film tinted with conventional blue paint. The conventional paint sample reached 75°C, however the researcher’s sample piece managed to maintain a temperature of around 42°C.
Further numerical simulations and experimental measurements of the films confirmed the samples were capable of cooling colourful objects not only to a temperature of 2°C below ambient temperature, but also with ultra-high saturation (100%) and a wide range of viewing angles (±60°).
According to the researchers, the multi-layered cooling films have significant potential for improving energy sustainability not only in vehicles, but also in buildings, facilities and equipment.
More information can be found in the paper titled ‘Cooling colours below ambient temperature’ published in the Optica journal.
