Bioinspired, Multiscale Reinforced Composites with Exceptionally High Strength and Toughness

Nature's multiscale reinforcing mechanisms in fabricating composite armors, such as seashells, provide lessons for engineering materials design and manufacturing. However, it is still a challenge to simultaneously add both micro- and nanoreinforcements in a matrix material since nano-fillers tend to agglomerate, decreasing their reinforcing effects. In this study, we report a new type of micro/nano hybrid filler, synthesized by an unconventional cotton aided method, which has B₄C microplatelet as the core and radially aligned B₄C nanowires as the shell. To enhance the bonding between the B₄C fillers and epoxy, the B₄C micro/nano-fillers were coated with a layer of polyaniline (PANI). With a low concentration of the PANI functionalized B₄C micro/nano-fillers (1 wt %), this B₄C/epoxy composite exhibited an exceptional combination of mechanical properties in terms of elastic modulus (∼3.47 GPa), toughness (2026.3 kJ/m³), and fracture strain (>3.6%). An analytical mechanics model was established to show that such multiscale reinforcement design remarkably enhanced the load carrying efficiency of the B₄C fillers, leading to the overall improved mechanical performance of the composites. This new design concept opens up a new path for developing lightweight, yet high-strength and tough materials with multiscale reinforcing configurations.