In Finland, a new nanoscale metasurface based on clouds could revolutionise heating and cooling. We speak to the professor responsible for this potential game-changer.
Our built environment continues to represent 39% of all energy related carbon emissions. Bringing this down is going to be incredibly challenging, not least given we are also facing mounting pressure to protect structures and their users from increasingly unstable temperatures.
The most logical solution to soaring thermometers is to stick the air-con on. However, this only adds more emissions to our rapidly heating atmosphere. So scientists are understandably rushing to develop new passive thermal management tools, and passivity — whereby heating or cooling takes place without consuming more energy — is often seen as the gold standard.
In a lab on the campus of Aalto University, Helsinki, one research team has been looking to the skies for inspiration as to how we can shield ourselves from the sun’s rays more effectively. Clouds, and specifically bright white cumulus and the grey-black cumulonimbus, set the precedent for much of what Professor Mady Ebahri and cohorts are currently working on. The former have a cooling effect, reflecting heat back, while the latter absorbs heat, preserving and increasing temperatures.
Based on this, research at Aalto has led to the development of a nanoscale ‘cloud’ metasurface which can alternate between white and grey ‘states’. You can ‘switch off’ inert cooling or heating capabilities, opening up a vast array of possible applications and use cases.
The technology relies on multiple scattering, absorption and polarizonic reflection principles which can modulate light and heat. Extensive backscattering is required to reflect and cool. Meanwhile, warming effects are achieved through sunlight absorption and storage.
In addition to temperature impact, both states are invisible under infrared light — a property that has never been present in a surface material before. Unlike conventional white paint used to cool surfaces, which simply reflect, in Professor Ebahri’s breakthrough the surface itself does not emit measurable heat. The grey surface acts the same in reverse — heating without emitting any detectable warmth.
‘We can now perhaps understand how this story can change global atmospheric heating and cooling. With this information, we are writing a new line in this story. Perhaps this can help us take steps to prevent global warming,’ he says.
‘Secondly, you can adapt our work to use on your house, use it on facades, to cool the home or keep it warm,’ Ebahri continues. ‘So heating and cooling in the city, in buildings, all of these could, in fact, be achieved with our technology. Third one, your clothes. This could be a useful material for many settings. And the last [application], which I don’t like too much, is military — camouflage.’
As our conversation continues it quickly becomes clear that Egyptian-born Ebahri has strong feelings about this final use case. Holding dual citizenship — with German and Palestinian passports — it’s not surprising to hear his disparaging comments about the use of potentially life-saving, climate-positive science by the defence industry. Nor should it raise eyebrows to learn about his views of politicians in general: ‘lower in intelligence’ and guilty of excluding scientists from relevant policy decisions.
‘We should work together on how to make a better place to live, and that’s exactly what we need to look at it — how we can really resolve tension, and how we can resolve problems we have in the climate, or help people who are not able to eat,’ says Ebahri.
‘Imagine that we have a real situation where the people are cooperating to live together? So we are solving the problem together,’ he adds. ‘We are thinking together. We are helping each other in this way. I guess it will be much greater than what they are doing at the moment.’
Putting our heads back into the clouds from the brutal reality of a world that seems to value and and want to expedite the destructive and divisive ofer the constructive, we ask about next steps for the Aalto team. Despite the complex science involved, the response is reassuringly simple.
‘My next step now, to be honest, is to prove other stuff linked to the Earth’s atmosphere and how this could be emulated at a nano scale,’ says Ebahri. ‘I don’t need to go to NASA to see what they are doing, I can emulate it here in the lab.’
Images: Aalto University
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