Dynamic Wettability Behavior of Emerging Ultrawhite Radiative Cooling Paints

Abstract

Outdoor radiative cooling surfaces passively lose heat by reflecting solar irradiation and emitting infrared radiation to cold deep space through the atmospheric sky window (8–13 µm), thereby achieving sub-ambient temperature. Ultrawhite radiative cooling paints are an emerging technology offering scalable solutions for cooling and passive water harvesting wherein surface wettability plays a key role. This work, examines how radiative cooling paint pigment and binder formulations affect surface morphology, roughness, and dynamic wettability. Samples are prepared with three different nanoparticulate pigments, calcium carbonate (CaCO₃), barium sulfate (BaSO₄), and hexagonal boron nitride (hBN); two binders, including an acrylic and a waterborne silicone-modified polyurethane dispersion (SILIKOPUR 8081); and pigment solid volume concentrations from 0% to 80% v/v. The CaCO₃ and BaSO₄ pigments produced paints with rougher textures and higher contact angles due to their pigment particle morphology. While high solar reflectance was achieved across various pigment and binder combinations, wettability exhibited a complex trend with pigment concentration, indicating that maximizing reflectance does not necessarily optimize wetting behavior. This expanded understanding on how pigment type, binder and concentration influence wettability, offering pathways to design coatings with tailored spectral and wetting properties for both self-cleaning paints and passive water harvesting applications