Modulus Interfacial Layer via Alternating "Rigid-Flexible" Structures: Enhancing Interfacial and Mechanical Properties of CF/PPESK Composites

Aiming at the problems of low bonding strength and large modulus difference at the interface between carbon fibers (CFs) and resin matrix, this research achieved in-situ growth of an adhesive "metal-phenolic" complex network (TA@Fe 3+ ) on CFs surfaces. Additionally, a modulus gradient transition layer featuring alternating "rigid-flexible" interlayer structures ((TA@Fe 3+ -GO) 2 ) was further constructed. The flexible TA@Fe 3+ complex network boosts chemical bonding at the fiber-resin interface, whereas the rigid GO enhances load transfer and dispersion. Through the synergistic effect of "interfacial adsorption-physical reinforcement", the interfacial strength is improved. The alternating “rigid-flexible” interfacial layer reduces the modulus mismatch between CFs and the resin by expanding the interfacial phase thickness and slowing the modulus decline rate, thereby minimizing interfacial stress concentration. Compared with UCF/PPESK composites, the modified composites exhibit a 40.4% increase in flexural strength and a 70% increase in interlaminar shear strength (ILSS). This study offers novel perspectives on the design of multi-level gradient modulus interlayer structures and the fabrication of strong-interfacial carbon fiber-reinforced polymer matrix composites (CFRPs).