Durable daytime radiative cooling achieved by super-slippery coatings containing polydimethylsiloxane brushes

Abstract

Radiative cooling technology is an effective method for mitigating global warming and the urban heat island effect. It achieves cooling through self-radiation and reflection solar energy without consuming energy. However, preparing a long-lasting and durable radiative cooling material remains a challenge. Here, we prepared a super-slippery radiative cooling (SSRC) coating with self-cleaning capability and mechanical stability for future large-scale and long-lasting applications of radiative cooling. The coating containing epoxy, polydimethylsiloxane (PDMS) brushes, and TiO2 exhibit high solar reflectance and infrared emissivity. Especially, the surface microstructures of the coatings enhance the emissivity in the atmospheric window. The high solar reflectivity (90 %) and infrared emissivity (93 %) of the SSRC coatings ensure effective cooling, with coatings on metal surfaces cooling down to an average of 10.4 °C outdoors. For the fruit preservation, the SSRC coating can even extend the shelf life of fruits by up to 10 days. More importantly, due to the low surface energy and high mobility of PDMS brushes, the coating exhibits excellent super-slippery and self-cleaning performances. Water and oil can easily slide on the surface of the SSRC coating. This approach prevents the coverage of contaminants, which is crucial for using radiative cooling coatings outdoors. Furthermore, the SSRC coating exhibits exceptional mechanical stability and can maintain a consistently low coefficient of friction during a 5-hour tribological test. After being impacted with water and sand outdoors for a long time, the coating retains its cooling and self-cleaning properties. Such durable and self-cleaning radiative cooling coating has potential for future applications in thermal management.