Switchable Surface Coating for Bifunctional Passive Radiative Cooling and Solar Heating

Abstract

The ability to achieve dual-mode thermal regulation for switchable heating and cooling on a single platform has thus far been challenged by the availability of suitable materials. The materials need to possess both high solar reflectance and high transmittance, necessitating large and small thicknesses in the same coating layer, respectively (i.e., the thickness constraint). Herein, for the first time, a single-layer coating made in a facile one-step process is reported, which exhibits rapid switch between high solar reflection (≈96.6%) and high solar transmission (≈86.6%). In the dry state, high solar reflectance and infrared (IR) emittance (>96% from 8 to 13 µm) enable passive radiative cooling, resulting in all-day near/sub-ambient temperatures in the demanding weather conditions of the tropical climate. Upon wetting, high transparency in the broadband range (0.3-2.5 µm) allows solar heating, leading to switchable thermal regulation. Such unprecedented performances are achieved through a unique hierarchical porous structure comprising of vertically aligned microscale pores in nanoscale pore matrix. This structure breaks the thickness constraint and broadens its applicability, in particular for seasonal areas with large temperature variation throughout the day.

Micro‐Nano Porous Structure for Efficient Daytime Radiative Sky Cooling

“…Recently, Fei et al also developed the promising PVDF coolers for switchable working, e.g., radiative cooling and solar heating. [78] The porous cooling film can achieve a high solar reflectance of ≈96.6% and an infrared emittance of >96% in dry state, which can result in sub-ambient cooling performance. when working in wet state, the films exhibit a high transparency of 86.6% in solar band, enabling the strong solar heating and a maximum above-ambient temperature of ≈47 °C.…”

Droplets in soft materials

“…Passive daytime radiative cooling is an emerging technology for thermal management. [101][102][103][104][105] Recently, it has been proved that porous polymer coatings show a good radiative cooling effect because the heterogeneous structures can induce serious solar reflection but allow for long-wave infrared emission. Since the volatilization of the liquid in the droplet-embedded soft materials will lead to porous structures, it constitutes a powerful method for preparing radiative cooling coatings.…”

“…Passive daytime radiative cooling is an emerging technology for thermal management 101–105 . Recently, it has been proved that porous polymer coatings show a good radiative cooling effect because the heterogeneous structures can induce serious solar reflection but allow for long‐wave infrared emission.…”

Bio‐inspired Copper Kirigami Motifs Leading to a 2D–3D Switchable Structure for Programmable Fog Harvesting and Water Retention

“…[1,2] However, rapid population growth, extreme climate change, and environmental pollution mean that more than four billion people suffer from severe water scarcity. [3] In response to this water scarcity, various advanced materials and functional devices have been utilized, including those related to water collection (from rainwater, [4] moist air, [5] or water vapor [6] ) and water purification (desalination, [7] filtration, [8][9][10][11] or adsorption [12][13][14] ). Fog flow represents a common water source that contains ≈13 000 trillion liters; thus, it is a promising resource that may help society successfully deal with waterrelated challenges.…”