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Researchers have revealed details of a new paint that reflects 96 per cent of the sun’s heat, meaning it leaves a building’s walls 6C cooler than the surrounding air.

According to an article published in the journal Science, this paint could greatly reduce the need for air conditioning.

It is common knowledge in the HVACR industry that cooling buildings accounts for a significant proportion of electricity consumption — a major contributor to global warming.

Currently, air conditioning accounts for 10% of global energy consumption. Researchers at Columbia University and Argonne National Laboratory in the US said their polymer “paint” could be used in combination with conventional air conditioning.

They have created a film of polymer with nanometre- and micrometre-sized air voids trapped inside.

“There are a lot of examples of substances that are white from air voids – like snow for example,” according to Nanfang Yu, associate professor in Applied Physics at Columbia University in the US.

“Snow is white because there are a lot of air bubbles inside, otherwise you have ice which is transparent – it’s as simple as that. We are just pushing this to the extreme by this chemical process.”

The solution process they use is based on “phase inversion” and involves mixing the polymer with a solvent alongside water, in which the polymer is insoluble.

After painting the mixture onto a surface, the solvent evaporates leaving just the polymer interspersed with water droplets. Finally the water evaporates leaving air voids.

Adjusting the percentage of water in the mix allows precise control over the size and density of the air voids, so that they can be tuned to maximize reflection of solar energy.

In addition the micrometre-sized voids give the coating a thermal emissivity close to that of a black body, that is, a perfect radiator of heat. This high thermal emissivity of the polymer coating can be used to cool objects that are already hot.

 

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