Construction of efficient passive radiative cooling emitter with selective emission in the whole atmospheric window and durable anti-contamination performance

Abstract

Polymer-based radiative cooling emitters (RCE) can drop the surface temperature lower than that of ambient without any external energy input, while the optical performance and application is limited. In this work, with the aim of enhancing the selective emission within atmospheric window and anti-contamination of the polymer coating in RCE, a super-hydrophobic bilayer RCE has been designed and prepared. Firstly, series of selected particles were embedded into a thin Polymethylpentene (TPX) composite polymer film. Then, the film was coated onto a high-reflective aluminum sheet. Next, the surface of the RCE was modified by particles (mica and TiO2) deposition and hexadecyltrimethoxysilane (HDTMS). As a result, the absorption peak was broadened to the whole atmospheric window region, and the anti-contamination performance was achieved with enhanced water contact angle of 159°. Moreover, the contact angle showed negligible change after continuous contaminated and cleaned processes. Besides, the RCE can also retain the selective emission and super-hydrophobic performance after exposed to UV-irradiation. During outdoor measurement, the RCE can drop the temperature below the ambient with a temperature difference of ~6 °C during the whole day. Super-hydrophobicity also can gain the RCE better cooling performance under high relative humidity, with a temperature of 2–3 °C larger than the hydrophilic RCE. The successful combination of cooling and anti-contamination functions endows our designed the polymer-based RCE the potential of practical application to serve as a multifunctional and long life passive RCE.