Materials that cool sustainably

In 2020, a construction company approached materials scientist Bivas Saha with a problem. The high summer temperature in the United Arab Emirates (UAE) was heating up building materials, the UAE-based construction company RAKNOR told Saha, urging him to develop a coating material that could reduce the surface temperature. The coat would employ radiative cooling to reflect and emit incoming heat radiation into space. The company reasoned that Saha, a PhD in material sciences with expertise in optics and nanophotonics, could develop such a material.

Radiative cooling could be the key to solving the larger problem of urban heat islands. "All these buildings — the concrete, these pavers, all of them — heat up and create an island of hot air, and the circulation of this hot air around the cities increases the temperature," explains Saha, Associate Professor at the Bengaluru-based Jawaharlal Nehru Centre for Advanced Scientific Research.

Building materials absorb and retain heat; skyscrapers restrict the outflow of heat, worsening the situation. Heat emissions from cars and factories add to the problem, as do active cooling devices such as refrigerators and air conditioners, which keep the indoors cool by absorbing heat but increase the heat outside. The increase in temperatures leads to a greater demand for cooling devices, which, in turn, leads to more heat.

The world has been looking for effective methods to cool the planet without consuming energy. Indicatively, urban planning focuses on green covers, natural ventilation, shading, and water fountains. People use insulated panels and white paints on terraces to keep the indoors cool. The hunt is now on for materials that can effectively maintain a cool atmosphere without the use of power.