A Superhydrophobic Dual-Mode Film for Energy-Free Radiative Cooling and Solar Heating

Abstract

Traditional electric cooling in summer and coal heating in winter consume a huge amount of energy and lead to a greenhouse effect. Herein, we developed an energy-free dual-mode superhydrophobic film, which consists of a white side with porous coating of styrene-ethylene-butylene-styrene/SiO 2 for radiative cooling and a black side with nanocomposite coating of carbon nanotubes/polydimethylsiloxane for solar heating. In the cooling mode with the white side, the film achieved a high sunlight reflection of 94% and a strong long-wave infrared emission of 92% in the range of 8–13 μm to contribute to a temperature drop of ∼11 °C. In the heating mode with the black side, the film achieved a high solar absorption of 98% to induce heating to raise the air temperature beneath by Δ T of ∼35.6 °C. Importantly, both sides of the film are superhydrophobic with a contact angle over 165° and a sliding angle near 0°, showing typical self-cleaning effects, which defend the surfaces from outdoor contamination, thus conducive to long-term cooling and heating. This dual-mode film shows great potential in outdoor applications as coverings for both cooling in hot summer and heating in winter without an energy input.

Advances in photothermal regulation strategies: from efficient solar heating to daytime passive cooling

“…35g). 553 In the cooling mode, the white side was facing out, achieving a temperature drop of more than 6 1C under a light intensity of 700 W m À2 . In the heating mode, the temperature was raised by B40 1C under 1 sun in a simulated cold environment (À20 1C), much higher than that of the surrounding air.…”

“…Likewise, porous coatings consisting of copolymer styrene–ethylene–butylene–styrene and SiO 2 as cooling surfaces and nanocomposite coatings having CNTs/PDMS as heating surfaces are also reported. 281 Besides, a Janus phonic thermal system was prepared by a non-solvent induced phase separation and one-step spray method. 282 Three materials Si 3 N 4 , SiO 2 , and PDMS which possess high IR radiation at various wavelengths and low solar absorption abilities were selected for the cooling side to broaden the emission range.…”

Recent advances in dynamic dual mode systems for daytime radiative cooling and solar heating

“…Nevertheless, due to the high solar thermal conversion efficiency of such materials, the heating side in the dual mode system still maintains a temperature above ambient. 86 Examples of such materials include graphene, 87 carbon nanotubes, and carbon black. According to eqn (4), to achieve the temperature increase, the value of P net needs to be less than 0.…”

Integration of daytime radiative cooling and solar heating

“…Owing to this principle, the current development of mechanical regulation is mature in terms of performance and stability compared with the above-mentioned two methods. Thus far, several methods for achieving mechanical regulation have been developed, such as roll-to-roll, 12 Janus, 21 , 22 , 23 , 24 switchable, 25 , 26 , 27 and programmable. 28 Zhao et al.…”

“…Although this field has been widely explored in the past few years, it is still in its early stages. To further promote research in this field and effectively solve its problems, we summarize the previous results from two aspects, switch mode (including electrical, 13 , 14 , 15 thermal-responsive, 16 , 17 , 18 , 19 , 20 and mechanical regulations 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ) and collaborative mode, 29 , 30 and introduce their principles, characteristics, and progress. In addition, unresolved scientific and technical issues associated with the outlook are presented in this paper.…”