Highly Efficient Infrared Stealth Asymmetric-Structure Waterborne Polyurethane Composites Prepared Via One-Step Density-Driven Filler Separation Method

Highly efficient infrared (IR) stealth materials with low emissivity and thermal insulation features are urgently demanded in many fields. However, these two characteristics are difficult to be realized by an individual compound due to the high thermal conductivity of low emissivity materials (e.g. metal materials) and the high emissivity of excellent thermal insulation materials (e.g. polymer foam and aerogel). Herein, we demonstrated a new strategy to fabricate low emissivity/thermal insulation IR stealth composites with asymmetric structure based on a combination of silver-plated hollow glass microsphere (HGM-Ag) and waterborne polyurethane (WPU) through one-step density-driven filler separation coupled with freeze-drying method. The composites were constructed from the HGM-Ag concentrated on the top of the composites as low emissivity layer and the bottom layer with low thermal conductivity about 0.044 W m(-1) K-1 served as the thermal insulation layer. The emissivity of the composites can be reduced from 0.943 to 0.713 by adding HGM-Ag. Benefitting from the well interconnected 3-dimensional structure, the HGM-Ag/WPU porous composites also display outstanding mechanical property. We believe this work will provide a new strategy for designing highly efficient IR stealth materials based on synergetic mechanism of reducing emissivity and thermal insulation.