India, France, Australia, and many other countries across the globe have been experiencing a not-so-smooth summer over the past few years. Every year, the highest temperature increases and makes humans realise just how excessive the effects of global warming can be, albeit in the beginning. In the end, we might as well become human fries.The condition has also posed a challenge for scientists to figure out how to keep homes cooler amid the rising heat in order to prevent the air conditioners from bursting into flames. Now, as per a study, it shows that passive radiative cooling can keep objects under sunlight cooler without the need for any external energy.However, most of these objects are white, and all the buildings around the world cannot afford to turn white for the sake of architecture and appearances. If you use colours, well, they absorb more sunlight and thus radiate more heat. What to do then?For years, this question was left in a stagnant debate. But now it seems a team of scientists might have figured out a way. A study published in Nature Energy titled ‘One-step-process bilayer ethyl cellulose for full-colour sub-ambient daytime radiative cooling’ by Liu et al. points out that a bilateral-coloured ethyl cellulose coating derived from biomass and fabricated in a single casting step and by controlled drying-induced self-stratification has a solar reflectance of 97.0% and sub-ambient daytime cooling of up to 9°C under a solar intensity of 800 W/m². Meaning that you could still use bright colours and have the surface about 16 degrees Fahrenheit cooler than the air surrounding it.According to reports, the material is based on ethyl cellulose, a biomass-derived compound, produced by a single-step coating.In a single drying step, the coating segregates into two layers: a thin, dense top layer that produces colour via thin-film interference without contributing to solar absorption and a porous bottom layer that provides high solar reflectance and long-wave infrared emission.Moreover, this colour is not the work of pigments; it’s the work of the sun itself. The coating uses light interference to create colour without absorbing solar radiation.As per the study, in field trials in Hong Kong’s humid subtropical climate, the coating outperformed commercially available coloured paints and fluorescence-based colour coatings. With cities like Mumbai, Miami and others battling humidity, this coating could be a welcomed new system.While passive cooling cannot completely replace air conditioners, with hotter and longer summers in sight, this might be one of the many ways to reduce heat absorption in homes and offices.
