Staying Cool with Polymer Paint

Jyotirmoy Mandal, an applied physics PhD student at Columbia Univ., grew up in a household that received only 16 hours of electricity every day. In the fierce summer heat of Bangladesh, those hours spent without air conditioning were almost unbearable. At his grandparents’ village home, Mandal had no AC at all; the sunbaked tin roof covering his cottage transformed the interior into an indoor oven.

Today, Mandal is using his experiences to create a potential solution for countries where AC is a luxury. In conjunction with Yuan Yang and Nanfang Yu, researchers at Columbia Univ., Mandal has developed a paint-like polymer that can cool homes by reflecting more than 96% of sunlight.

At the same time, the paint emits thermal radiation to keep the polymer cooler than the surrounding air. His work was also partially inspired by earlier research on Saharan silver ants published by Yu.

According to Mandal, Saharan silver ants come out to forage during the hottest time of the day to avoid predators, and can do so because they have a dense array of triangular cross-sectioned hairs. These hairs scatter and reflect sunlight and emit thermal radiation; the radiative cooling effect keeps the ants cool, allowing them to survive the intense desert heat.

Mandal’s paint-like polymer also reflects light and emits radiation — the polymer is a type of passive daytime radiative cooling (PDRC) technology. The central focus of PDRC is to reduce energy costs associated with expansive use of air conditioning — research in the field usually concerns limiting fossil fuel use. The new polymer departs from previous PDRC methods, which are either less efficient or have limited applicability,...