Buildings spent over 30% of their energy use to heating, cooling, and lighting methods. Passive designs, including fresh roof paints, have gone a long way toward lowering this usage, and its impact on the atmosphere and climate, however, they’ve one fundamental limitation—they are often static, and thus not responsive to every day or seasonal changes.
Columbia Engineering researchers have produced porous polymer coatings (PPCs) that enable cheap and scalable ways to manage heat and light in buildings. They took advantage of the optical shift-ability of PPCs in the photovoltaic wavelengths to regulate solar heating and daylighting and expanded the concept to thermal infrared wavelengths to modulate heat emitted by objects. Their study is published on October 21, 2019, by Joule.
The team’s model is similar to smart windows, however, with a higher optical switchability, and is built utilizing simpler, cheap supplies that could make it implementable at large scales. It models upon earlier work that showed a paint-like fluoropolymer coating with nano-to-microscale air voids that can cool down buildings.
The group started their work on optically shifting PPCs serendipitously when Mandal saw that a couple of drops of alcohol spilled on a white fluoropolymer PPC turned it transparent.
A porous material like paper seems white because the air within the pores and has a unique refractive index (~1) to that of the porous material (~1.5), inflicting them to spread and reflect light.