A Dual Strategy of Viscosity Modulation and Directional Freezing toward Multifunctional ZnMgAl-LDH/Chitosan Hybrid Aerogels

Aerogels, as highly efficient thermal insulation materials, exhibit significant potential for applications in building exterior insulation, power battery thermal protection, and aerospace thermal management. However, conventional polymer aerogels possess inherent limitations in thermal insulation performance, mechanical compressive strength, and flame-retardant safety, which impede their widespread engineering adoption. Herein, we propose a synergistic fabrication strategy integrating directional freezing and viscosity modulation. By precisely regulating the temperature gradient and incorporating layered double hydroxides (ZnMgAl-LDH) to tune the viscosity of hydrogel precursors, we enhanced the viscous resistance during ice crystal growth, thereby refining ice crystal dimensions. A honeycomb-like ZnMgAl-LDH/chitosan (CS) inorganic-organic hybrid aerogel with tunable pore size distribution was successfully constructed. The superlattice interface of ZnMgAl-LDH and the organic-inorganic hybrid interface synergistically reinforce phonon scattering (covering both long and short wavelengths), effectively suppressing solid thermal conduction and significantly improving the aerogel's thermal insulation performance. Compared with pure CS aerogel, the hybrid aerogel with optimized pore size displays a lower thermal conductivity (0.03735-0.03936 W/(m·K)) and reduces the surface temperature by 6.9 °C under identical conditions. Moreover, the honeycomb microstructure endows the hybrid aerogel with excellent compressive resilience, retaining 72.4% stress after 50 compression cycles and achieving a compressive modulus 9 times higher than that of pure CS aerogel. Its flame-retardant performance is remarkably enhanced, with the limiting oxygen index (LOI) increasing from 21.5% to 41.4% (meeting high flame-retardant standards) and the peak heat release rate (PHRR) decreasing by 74.9%. Additionally, the hybrid aerogel exhibits superior hydrophobicity and environmental durability, highlighting its great potential for practical engineering applications.