High strength in combination with high toughness in layered intrinsic heterocyclic aramid films via constructing liquid crystal-like structure during gelation self-assembly

Abstract

The fabrication of high strength and toughness in polymeric materials, especially for rigid-chain polymers, has been a long-term technological challenge in high-performance materials design. In this work, the synthesized soluble poly (benzimidazole-terephthalamide) (PABI) acts as a rigid-chain intrinsic polymer. Then, the coordination effect of the HCl with the benzimidazole unit induces more extended PABI chains assembled into a gel network with a liquid crystal-like structure. Finally, the obtained PABI gel is further compressed into a layered film during solvent evaporation. Scanning electron microscopy images reveal that the resultant films present nacre-like morphologies. X-ray diffraction and polarized light microscopy demonstrate the formation of the liquid crystal-like structure. Owing to the highly oriented layers and the self-reinforcement of fibrils in layers, the strength (511.1 MPa) of PABI films increases by 41.7% through altering the gelation time. Ultimately, it reaches a record-high 708.7 MPa by altering HCl content. Meanwhile, the sliding and plastic deformation of amorphous interconnected layers, tearing of fibrils, crack branching, and crack deflection facilitate stable crack propagation and significantly dissipate the energy. Hence, the toughness (136.7 MJ/m3) of PABI films also increases by 23.7% through altering gelation time and remains at a high level under high HCl content. In addition, the highly oriented layered structure unexpectedly imparts PABI films with a high dielectric strength of 686.6 MV/m. Our findings provide a facile strategy for designing high-performance polymeric materials with high strength, toughness, and even more functionality.