Dielectric microsphere coatings for passive daytime radiative cooling (PDRC) are gaining attention owing to their low cost and potential for mass production. The cooling performance could be further enhanced to effectively reflect solar radiation and emit thermal radiation to the cold sky by designing microspheres suitable for PDRC applications. Hollow dielectric structures were numerically designed to enhance the PDRC performance of dielectric microsphere coatings. The maximum solar reflectance (R¯solar = 0.96) was obtained with a fill rate f = 0.6, outer radius rout = 0.5 μm, core–shell rate φ = rin / rout = 0.3, thickness t = 300 μm, and thermal infrared emittance ε¯LWIR = 0.90. Furthermore, by controlling the multisize sphere distribution within φ = 0.1 to 0.5, the cooling performance at t = 300 μm was enhanced to R¯solar = 0.98, ε¯LWIR = 0.95, and a net cooling power of 77 W / m2 was achieved at a temperature of 25°C, which was ∼38 % higher than that achieved with the single-size sphere coating (φ = 0.3) and ∼64 % higher than that of the solid SiO2 sphere coating (φ = 0). These results indicate that hollow structures can effectively enhance the cooling performance of dielectric microsphere coatings by increasing the number of interfaces between the air and dielectric materials.
Radiative cooling is an emerging strategy to achieve cooling without using electricity, where a surface has high solar reflectance and high thermal emittance simultaneously. Porous polymer paint is a scalable approach to realize radiative cooling. For instance, porous poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP)) coatings exhibit near-perfect solar reflectance Rsolar (> 0.96) and long-wave infrared (LWIR) emittance εLWIR (~ 0.97) for radiative cooling. In this presentation, I will discuss the principle, manufacturing of such porous film. Methods to switch the optical/thermal properties from radiative cooling to solar absorption will also be discussed, which represents an “ice-house” to “green-house” transition useful for tuneable radiative cooling at night and potentially, thermal camouflaging. At the end, strategies to achieve colored radiative cooling will be discussed too
Radiation damage is a topic typically sidestepped in formal discussions of characterization techniques utilizing ionizing
radiation. Nevertheless, such damage is critical to consider when planning and performing experiments requiring large
radiation doses or radiation sensitive samples. High resolution, in situ transmission X-ray microscopy of Li-ion batteries
involves both large X-ray doses and radiation sensitive samples. To successfully identify changes over time solely due to
an applied current, the effects of radiation damage must be identified and avoided. Although radiation damage is often
significantly sample and instrument dependent, the general procedure to identify and minimize damage is transferable.
Here we outline our method of determining and managing the radiation damage observed in lithium sulfur batteries
during in situ X-ray imaging on the transmission X-ray microscope at Stanford Synchrotron Radiation Lightsource.
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