Constructing interfacial pulleys with branched polynaphthalamic acid polyrotaxane: a new route to superior interfacial toughness and strength in carbon fiber-reinforced composites

Alleviating the modulus mismatch and residual stress at the interphase of carbon fiber-reinforced polymer matrix composites (CFRPs) is crucial for enhancing their interfacial and mechanical performance. In this study, interfacial pulley structures were strategically engineered through the development of branched polynaphthalamic acid-based polyrotaxane (BPP), thereby enabling simultaneous enhancement of interfacial toughness and strength in CFRPs. Molecular dynamics simulations combined with comprehensive chemical structure characterization validated the rational molecular design and successful synthesis of BPP. Comparative analysis demonstrated that the BPP-modified carbon fiber/epoxy composites (BPPCF/EP) displayed a substantially increased interphase thickness of 412.50 nm compared to unmodified CF/EP (UCF/EP), along with a gradual modulus transition and a notable 78.15 % decrease in interfacial residual stress. These improvements stem from the synergistic effect of the naphthalimide anchor, which facilitates modulus gradient regulation, and the unique molecular pulley mechanism inherent to the BPP architecture. As a result, the transverse fiber bundle test strength (TFBT strength), interfacial shear strength (IFSS), and interfacial toughness of the BPPCF/EP were greatly improved by 158.57 %, 103.76 %, and 348.68 %, respectively, compared to the UCF/EP. This investigation establishes a novel materials engineering strategy for interfacial optimization in CFRPs, offering fundamental insights into the design of multifunctional interphase modifiers for high-performance structural composites.