Aluminum/waterborne polyurethane composite aerogels with combined low infrared emissivity and thermal conductivity

Abstract

Aerogels with combined low infrared emissivity and thermal conductivity hold promise in infrared stealth applications. Via density-induced filler sedimentation and freeze-casting, aluminum/waterborne polyurethane (Al/WPU) composite aerogels were prepared. The low emissivity layer of Al powders was self-formed at the bottom of the solution. An aligned porous structure perpendicular or parallel to the Al layer was constructed via vertical freeze-casting (VF) or horizontal freeze-casting (HF). For aerogels with a porous structure aligned perpendicular (named (Al/WPU)_VF) or parallel to the Al layer ((Al/WPU)_HF), the emissivity values in the 8–14 µm range are 0.31 and 0.49, respectively. On a hot stage of 100 °C with a duration of 10 min, the radiative temperatures of the aerogels with a thickness of 10 mm are 41.7 °C and 44.6 °C, respectively. Tests on the compressive stress–strain behavior were performed in the direction perpendicular to the Al layer. The compressive moduli of the aerogels are 46.4 kPa and 3.9 kPa, respectively. Finite element simulation was carried out to reveal the deformation mechanism and stress–strain behavior. The study offers a solution for the design and preparation of aerogels with combined low infrared emissivity and thermal conductivity.