Polyimide composite films with low surface reflection via spontaneous surface segregation of silica hollow nanoparticles

Polyimide (PI) composite films incorporating silica hollow nanoparticles (SHN) were successfully fabricated, exhibiting a distinct asymmetric structure. The surface morphology, composition, optical properties, and mechanical performance of the films were systematically investigated. Scanning electron microscopy and atomic force microscopy confirmed the preferential segregation of SHN toward the top surface, attributed to their low density and high surface activity. This led to a rougher top surface with a higher SHN concentration, while the bottom surface remained relatively smooth with a dominant PI phase. Optical measurements revealed a significant reduction in reflectance, particularly on the rough top surface, while maintaining high transmittance. Mechanical analysis, including tensile testing and nanoindentation, demonstrated that SHN incorporation enhanced the elastic modulus and hardness of the films, with the bottom surface exhibiting superior mechanical properties due to the compact stacking of PI and SHN. These findings provide valuable insights into the structural design of antireflective PI composite films and underscore the critical role of hollow nanoparticle surface activity in determining film morphology and functionality.