Aerogel/Hollow Glass Microsphere-Filled Styrene–Acrylic Composite Thermal-Insulating Coating for Architectural Decoration and Its Fabrication Mechanism

Hydrophobic silica aerogel was synthesized from a water-glass precursor via CO2-mediated carbonation. A water-based dispersion strategy was adopted to incorporate silica aerogel and hollow glass microspheres (HGMs) as dual insulating fillers into styrene–acrylic emulsion, yielding composite architectural coatings with hierarchically porous architecture. The impacts of filler loading and mass ratio on thermal-insulation performance were systematically explored. The optimized composite coating delivers a low thermal conductivity of 0.035 W/(m·K) and retains good thermal stability up to 350 °C. The outstanding thermal-insulating capability originates from the synergistic effect between macropores of hollow glass microspheres and nanopores of silica aerogel. Aerogel nanoparticles fill inter-particle voids among stacked hollow glass microspheres, break thermal-bridge conduction pathways, and suppress heat transfer by virtue of the intrinsically ultralow thermal conductivity of aerogel. Such structural features effectively mitigate both solid heat conduction and internal convective heat transfer within the coating matrix. This work establishes a facile, scalable route to fabricate gel-derived hierarchically porous thermal-insulating materials, showing promising applicability for functional decorative coatings in building energy-saving scenarios.