Maxwell-Garnett permittivity optimized micro-porous PVDF/PMMA blend for near unity thermal emission through the atmospheric window

作者：Wong, Ross Y. M.; Tso, C. Y.; Fu, S. C.; Chao, Christopher Y. H.^*

来源：Solar Energy Materials and Solar Cells, 2022, 248: 112003.

DOI：10.1016/j.solmat.2022.112003

• Radiative cooling
• Disordered heterogeneous materials
• Light -matter interaction
• Thermo -optics
• Electromagnetism
• Effective medium theory

Owing to excellent solar reflectivity and sky window emissivity, disordered heterogenous materials, including filler-abundant matrices, paints, and coatings, as well as foam-like, fiber-stacked and composite porous struc-tures, form a major class for efficient passive radiative cooling. Contrary to well-established empirical under-standing, this work offers a generalized analytical overview of their macroscopic thermo-optical properties from the microscopic electromagnetic perspective of Maxwell-Garnett effective medium theory. With the family of micro-porous poly(vinylidene-fluoride)/poly(methyl-methacrylate) blends as a representative example, pro-cedures for tailoring mid-infrared spectral emissivity via effective permittivity are outlined. Theoretical frame-work and design scheme are validated by finite difference time domain simulation and Fourier transform infrared spectrometry. It is shown that poly(vinylidene-fluoride) and poly(methyl-methacrylate) form a pair of comple-mentary constitutive materials for near unity thermal emission through the atmospheric Optimized binary polymeric blend, prepared by spray-coating method, features a window emissivity of 98% and realizes nocturnal radiative cooling with a temperature reduction of 6.8 degrees C and a cooling power of 94 W/m2 in an outdoor field investigation. It can serve as a promising bifunctional material for simultaneous radiative heat dissipation and capacitive energy storage, which meets the demand for nocturnal, radiative cooling aided thermoelectricity generation and storage potential.