Multifunctional high fatigue resistant silica aerogel reinforced by polyurethane via ambient pressure drying for improved thermal and sound insulation, water proofing, and vapor permeability

This study investigates the reinforcement of silica aerogels (SAs) with urethane-structured chains of varying molecular weights to enhance their fatigue resistance, thermal insulation, sound absorption, hydrophobicity, water resistance, and water vapor permeability. Silica aerogels reinforced with diols (SA/76D, SA/4000D) and triols (SA/92 T, SA/4000 T), which have molecular weights corresponding to their respective numbers, were synthesized via ambient pressure drying. Fatigue resistance was notably improved, with SA/76D exhibiting a 52.61 % reduction in compressive stress after 500 cycles, compared to complete structural failure in neat SA. The thermal conductivity of SA/4000D (29.89 mW/m center dot K) was slightly higher than that of neat SA (27.28 mW/m center dot K) due to smaller pores created by higher molecular weight urethane-structured chains, which limit heat transfer. Sound absorption coefficients of SA/4000D (0.45 at 1600 Hz) and SA/4000 T (0.46 at 2000 Hz) surpassed that of neat SA (0.34). These improvements are attributed to the hierarchical pore structures influenced by the molecular weight of the urethane-structured chains. Smaller pores created by higher molecular weight chains enhance thermal conductivity by limiting gas particle conduction. Hydrophobicity, enhanced by urethane chain reinforcement, increased water contact angles from 129.1 degrees (neat SA) to 137.1 degrees (SA/4000D), improving water resistance and reducing susceptibility to moisture absorption. Despite improved hydrophobicity, water vapor permeability was significantly enhanced (3412 g/m2 center dot day for SA/4000D vs. 1871 g/m2 center dot day for neat SA), indicating better breathability. Furthermore, hierarchical pore structures significantly contribute to mechanical strength by forming uniform, interconnected networks that efficiently distribute stress and resist deformation. These findings demonstrate the interplay between the molecular weight of urethane-structured chains, pore structure, and aerogel properties, highlighting the optimized balance of fatigue resistance, thermal insulation, sound absorption, hydrophobicity, water resistance, and water vapor permeability, making these hybrid silica aerogels ideal for advanced building materials.