Micro- and Nanoporous Polymer Coatings: A Diverse and Promising Platform for Optical and Thermal Regulation

Polymers vary widely in their intrinsic optical properties – for instance, poly(ethene) (PE) is highly transparent across the visible to far-infrared wavelengths, while poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP) is highly emissive in the long-wave infrared (LWIR). When made porous, polymers optically scatter sunlight. As a result, porous P(VdF-HFP) can attain solar reflectance (R_solar) > 96% and LWIR emittance (ε_LWIR) ~ 97%, which makes it a near-perfect radiative cooler for buildings. Meanwhile, the high R_solar (~ 80%) and LWIR transmittance (~ 60%) of porous PE makes it useful in thermoregulation devices with tuneable ε_LWIR. Furthermore, by reversibly wetting and drying porous polymers with appropriate fluids, scattering efficiencies of the pores can be greatly altered to cause switching between solar reflective and transparent states (by 74%). Switching between LWIR transparent and absorptive/emissive states (by 60%) can also be achieved. Such optically switchable porous polymer coatings can control heat and light in buildings, and be used for camouflaging. Promisingly, porous polymers are already widely manufactured, making the stated applications viable.

J. Mandal et. al., Science 362, 315 (2018)
J. Mandal et. al. Adv. Funct. Mater. 28, 1802180 (2018)