Surfactant-free Fabrication of Macroporous Silicone Monoliths for Flexible Thermal Insulation

Hydrophobic silicone macroporous materials prepared in an aqueous solution by the sol–gel method have been considered for various applications such as separation media, heat insulators, and liquid nitrogen adsorbents. In the conventional preparation process, surfactants are used to suppress phase separation to obtain a uniform bulk material. However, a large amount of solvent and time is required to remove them before drying, which hinders industrial-scale synthesis. By copolymerizing tetra-, tri-, and bifunctional organosilicon alkoxides in an aqueous acetic acid–urea solution, flexible macroporous silicone monoliths were successfully obtained. The marshmallow-like monoliths recovered their original shape even after 80 % uniaxial compression and significant bending and water repellency. The thermal conductivity of those materials was ~0.035 W m⁻¹ K⁻¹ and did not increase even under 60 % uniaxial compression. This characteristic property can be used for thermal insulation on surfaces with various shapes and in confined spaces.