Constructing a Molecular Pulley Network Interphase for Simultaneous Enhancement of Interfacial Toughness and Strength in Carbon Fiber/Epoxy Composites

Simultaneous enhancement of interfacial toughness and strength in carbon fiber reinforced polymer matrix composites (CFPRs) is critical for achieving superior mechanical performance and long‐term durability. Herein, a multi‐aldehyde polyrotaxane (maPR) was synthesized and incorporated into the CFRP interphase at varying branched polyethyleneimine (PEI)/maPR ratios to construct a molecular pulley network. The 2:1 PEI/maPR formulation (PEI 2 ‐PR 1 ) generated an optimal molecular pulley network within the interphase of CFRP, which enhanced stress dissipation capacity while increasing interphase thickness and crosslinking density. Compared to the desized carbon fiber (CF‐desized), the PEI 2 ‐PR 1 ‐modified carbon fibers (CF‐(PEI 2 ‐PR 1 )) demonstrated significantly increased surface roughness and wettability. Consequently, the CF‐(PEI 2 ‐PR 1 )/EP composite exhibited the widest interphase (402 ± 8 nm), the highest transverse fiber bundle test (TFBT) strength (24.80 ± 2.21 MPa), interfacial shear strength (IFSS) (72.17 ± 2.99 MPa), and interfacial toughness (194.13 ± 2.43 J/m 2 ), along with the optimal release of residual interfacial stress (82.10%). This work proposed a novel and effective approach for simultaneously enhancing the interfacial toughness and strength of CFRP through molecular‐scale interphase engineering.