POSS/PVTMS aerogels for passive cooling and THz communication via cross-linking density regulation and nanoscale bimodal design

Super thermal insulation aerogel materials featuring nano-sized cavities, abundant heterogeneous interfaces, and low dielectric properties offer a promising avenue for the development of materials that excel in both passive cooling and high-frequency terahertz (THz) communication efficiency. In this work, a pre-polymerized vinyl trimethoxy silane (PVTMS) molecule with high cross-linking density was fabricated via radical polymerization, and then polyhedral oligomeric silsesquioxane (POSS) was used for tailoring the cross-linking density and polar functional group ratio of the PVTMS nano-aerogel system, simultaneously. The fabricated aerogels possessed a nanoscale bimodal structure including small (similar to 30 nm) and large (similar to 200 nm) pores, where the small pores lead to the nanoscale Knudsen effect and ultra-low thermal conductivity (lower than air), while the large pores induce the Mie scattering effect and enhance solar reflectance for radiation blocking. Thanks to the tailored nanostructure design, the POSS@PVTMS aerogel possessed a high specific surface area (728 m(2) g(-1)), ultra-low thermal conductivity (25.5 mW m(-1) K-1), hydrophobic properties (137 degrees water contact angle), high infrared emissivity (averaging similar to 99%), and ultra-low dielectric properties (average D-k = 1.13). Hence, the aerogel exhibited an enhanced passive cooling capability (Delta T reached 3.7 degrees C) along with an impressive THz transmission rate (average 88.7%).