A structural polymer for highly efficient all-day passive radiative cooling

Pang

et al. 2021

EcoMat

Passive daytime radiative cooling (PDRC) dissipates terrestrial heat to the extremely cold outer space without using any energy input or producing pollution. It has the potential to simultaneously alleviate the two major problems of energy crisis and global warming. In this review, we summarize general strategies implemented for achieving PDRC and various applications of PDRC technologies. We first introduce heat transfer processes involved in PDRC, including radiative and nonradiative heat transfer processes, to evaluate the PDRC performance. Subsequently, we summarize the general material designs used for controlling PDRC performance, such as tuning the thermal mid-infrared emittance and solar reflectance. Finally, we discuss the diverse applications of PDRC technologies to overcome problems in space cooling, solar cell cooling, water harvesting, and electricity generation.

Section: Improved Thermal Mid-infrared Emittancementioning

confidence: 78%

“…Source: Reproduced with permission: Copyright 2021, Spring Nature. 67 (I) Textile reflector based on the polymer (such as: PEO). Source: Reproduced with permission: Copyright 2021, Spring Nature 76…”

Section: Colored Pdrc Coatingmentioning

confidence: 99%

Passive daytime radiative cooling: Fundamentals, material designs, and applications

Pang

et al. 2021

EcoMat

“…When the thickness increases to the millimeter level, the transmittance almost decreases to zero and thus the emissivity reaches the maximum. [7,39] In this study, the nano-micro-structured plastic is different from the previously reported textiles or polymer films with the relatively thin thickness at the micrometer level; it is prepared with the thickness at the millimeter level. Therefore, the nano-micro-structured plastic's emissivity and radiative cooling efficiency are almost irrelevant to the millimeter-level thickness.…”

Section: Photonic Properties Of the Nano-micro-structured Plasticmentioning

confidence: 98%

Reconfigurable and Renewable Nano‐Micro‐Structured Plastics for Radiative Cooling

Gao

Lei

et al. 2021

Adv Funct Materials

Passive radiative technology enables sustainable cooling by synchronously emitting heat and reflecting solar light without any energy consumption. However, the consumption of non-recyclable and non-renewable radiative materials in large quantities may eventually cause resource waste and environmental issues. Herein, reconfigurable and renewable nano-micro-structured plastics for future eco-friendly and large-scale radiative cooling applications are developed. The plastics are facilely prepared from a locally confined polymerization method, which not only enables the customization of nano/micro-structures for thermal emission and sunlight reflection but also provides physically crosslinked networks for damage repairing, shape reconfiguration, and recyclable usage. Compared with traditional plastics applied on electronic devices, the nano-micro-structured plastic achieves much higher cooling efficiency with a temperature drop of 8.6 °C on electronic circuits and 7.5 °C cooling improvements under sunlight. With the excellent cooling performance and the recycling potential, the nano-micro-structured plastics open an environmentally sustainable pathway to address the thermal issues encountered by electronic devices and challenges of global warming.

“…[ 5,6 ] Currently, porous polymer structures without doped scattering particles are rising to replace such conventional nanoparticle composites. [ 7–9 ] Nevertheless, it is a grand challenge to make porous polymer structures with significant scattering ability due to the intrinsic low refractive index of polymers. In recent years, Cyphochilus scale made of biopolymer chitin has become an inspiration source for making highly scattering porous polymer films due to its excellent scattering performance stemming from refined porous network.…”

Section: Introductionmentioning

confidence: 99%

Biomimetic Porous Fluoropolymer Films with Brilliant Whiteness by Using Polymerization‐Induced Phase Separation

Huang

Fang

et al. 2021

Adv Materials Inter

Inspired by the Cyphochilus scale with extreme whiteness, fluoropolymer is used as the matrix to prepare highly scattering porous polymer films through polymerization‐induced phase separation (PIPS) method. The mixture used for the PIPS technique contains a fluoride monomer, a UV photoinitiator, and porogens (cyclohexanol and perfluorooctanol). By carefully tuning the mixture parameters (cyclohexanol–perfluorooctanol and monomer–porogen weight ratios), the porous morphology can be well tailored, which induces different scattering performances. With an optimized formulation (50 wt% monomer, 25 wt% cyclohexanol, and 25 wt% perfluorooctanol), the porous film with a thickness of 55 µm can achieve an average total reflectance of ≈90%, featuring a measured transport mean free path of 1.3–1.7 µm (comparable to the 1.5 µm of the benchmark Cyphochilus scale). Further, the porous films are applied to the light‐emitting diode (LED) device and it is demonstrated that they can effectively improve the light extraction efficiency of the LED and thus enhance the luminous performance. Due to the simplicity, cost‐effectiveness, and scalability of the PIPS method, the as‐developed porous fluoropolymer films with such excellent scattering ability can find many potential applications not only in the field of optoelectronics, but also in various complex scenarios, such as daytime passive radiative cooling.