Boehmite nanofiber–polymethylsilsesquioxane composite macroporous monoliths for high diffuse reflectance and improved machinability

Boehmite nanofibers (BNF)-reinforced Polymethylsilsesquioxane (PMSQ) composite macroporous monoliths were systematically optimized to achieve high diffuse reflectance, mechanical robustness, and machinability for optical applications. By varying the BNF content and methyltrimethoxysilane (MTMS) concentration, monolithic materials with controlled microstructures and tunable skeleton sizes were successfully fabricated. The optimized BNF–PMSQ monolith exhibited a diffuse reflectance of approximately 99.5% in the visible to near-infrared region of typical silicon photodiode detection (400–1100 nm), slightly exceeding the reflectance of the widely used diffuse polytetrafluoroethylene material (Spectralon). The improved mechanical properties facilitated precise machining by computer numerical control (CNC) milling and enabled fabrication into complex shapes using 3D printed molds by exploiting the chemical stability. The composite monolith exhibited surface hydrophobicity (static contact angle ~155°) and thermal stability up to 350°C without significant optical degradation, indicating potential suitability for outdoor applications. These results demonstrate that BNF–PMSQ macroporous monoliths are promising alternatives to traditional reflective materials, combining environmental compatibility, high optical performance, and versatile processing capabilities.