Construction and application of a composite microsphere with excellent thermal insulation properties

Thermal insulation materials play a crucial role in addressing the energy crisis and mitigating the urban heat island effect. As a hollow material possessing excellent elasticity and thermal insulation potential, thermally expandable microspheres (TEMs) can have their performance further enhanced through surface modification. In this study, bismuth oxide (Bi₂O₃) was innovatively combined with TEMs for the first time. By conducting in-situ polymerization of polyaniline (PANI) on the surface of TEMs, a positive surface charge was induced, enabling the electrostatic attraction and coating of Bi₂O₃ particles. This process successfully constructed Bi₂O₃/PANI/TEMs composite microspheres. The combination of Bi₂O₃ particles, which exhibits far lower thermal conductivity than other metal oxides, with the closed-cell spherical structure of TEMs, effectively suppresses heat convection and radiation. Furthermore, it significantly inhibits phonon conduction and enhances phonon scattering. The fabric coating prepared from these composite microspheres exhibited a thermal conductivity of only 0.042 W/(m·K). Compared to the TEMs, the near-infrared (NIR) transmittance was reduced by 39%, and an ultrathin composite coating of merely 500 μm in thickness increased the thermal insulation temperature of cotton fabric by 7.7 °C. Comparative analysis revealed that the Bi₂O₃/PANI/TEMs composite coating exhibits superior thermal barrier performance to expanded polystyrene (EPS) foam. Moreover, when incorporated into commercial coatings, it further enhanced their thermal insulation capability. This research provides a novel strategy and material system for developing new, highly efficient, and lightweight thermal insulation coatings, positioning the composite as a highly promising thermal insulation material.