Coherent nanofiber array buckling-enabled synthesis of hierarchical layered composites with enhanced strength

Heterogeneous materials possess unique combinations of strength, toughness, and multifunctionality, which are derived from the interplay between the different material constituents. The performance of such materials can be further improved via hierarchical architecting, including down to the nanoscale. Here, a novel hierarchical nanoengineered layered architecture is created by harnessing the coherent buckling of vertically aligned carbon nanotube (CNT) arrays followed by their integration with existing aerospace-grade carbon microfiber polymer-matrix advanced composites. In-plane tensile and interlaminar shear strengths are improved beyond the aerospace composite by ∼30% and 10%, respectively, and also beyond another CNT hierarchical architecture. Multiscale reinforcement mechanisms responsible for the strength enhancement, including nanofiber pullout, bridging, and suppression of delamination, are revealed by scanning electron microscopy and 3D X-ray computed tomography. The ability to design and create scalable, hierarchical materials with characteristic dimensions spanning from the nanoscale to the macroscale opens up a wide new avenue of next-generation advanced materials with enhanced mechanical and multifunctional properties.