Superhydrophobic polydimethylsiloxane composite coating for efficient and stable passive radiative cooling

Passive radiative cooling coating materials are easily damaged by aqueous contaminants, dust, UV irradiation, acid rain, salt mist, etc., which will weak the cooling effect in outdoor environments. In this work, a modified hollow glass microsphere (VHGM) was used as functional fillers, a superhydrophobic polydimethylsiloxane (PDMS) composite coating with stable and efficient passive radiative cooling was successfully constructed. The VHGM filler with siloxane chain and reactive vinyl group can entangle and covalently bond with PDMS chains, resulting in a better compatibility between the two components. Notably, the incorporation of 30 wt% VHGM can acquire high solar reflectance (0.914) and thermal emittance (0.951), producing sub-ambient temperature drops of 8.9 °C and 3.4 °C in outdoor daytime and nighttime environments, respectively. Moreover, the as-prepared PDMS-VHGM30 coating possessed a higher static water contact angle of 153° and a lower sliding contact angle of 9°, leading to the formation of superhydrophobic surface with desirable self-cleaning and anti-corrosion. After the treatments with muddy water, UV irradiation, acid or salt solution soaking, the PDMS-VHGM30 coating still remains above 93.5 % (daytime) and 95.0 % (nighttime) passive radiative cooling efficiency in comparison with the original sample, showing durable outdoor radiative cooling performance. The proposed PDMS-VHGM30 coating integrating radiative cooling with superhydrophobic self-cleaning, anti-corrosion and UV resistance characteristics may has practical applications on buildings, vehicles, and other terrestrial objects.