From Static Coating to Adaptive Interphase: A Tg-Mismatch-Driven Dual-Component Sizing Strategy for High-Temperature Thermoplastic Composites

Constructing fiber–matrix interfaces that simultaneously possess thermal stability and adaptive responsiveness remains a critical challenge for high-temperature thermoplastic composites. Herein, a Tg-difference-driven dual-component colloidal suspension sizing strategy is proposed to achieve controllable interfacial evolution in carbon fiber-reinforced poly(phthalazinone ether sulfone ketone) (CF/PPESK) composites. By codepositing a rigid poly(amic acid) salt (PAAs) precursor and a flexible sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) in an aqueous medium onto the carbon fiber surface, a spontaneous phase reconstruction occurs during hot-press processing due to differences in chain mobility and Tg. The high-Tg PI segments assemble into a rigid skeleton adjacent to the fiber surface, while the low-Tg PPESK segments interdiffuse with the matrix, forming a compliant penetration layer and molecular bridging structures. Such a synergistic interfacial architecture markedly enhances interfacial wettability, chemical compatibility, and mechanical stability. The resulting composites exhibit an interlaminar shear strength (77.6 MPa) and flexural strength (1705 MPa) that are increased by 41.3% and 43%, respectively, relative to the desized fibers, while retaining over 60% of the mechanical performance at 250 °C. AFM modulus mapping reveals a smooth modulus-gradient interphase of ∼300 nm, confirming the molecular interpenetration and dynamic reconstruction mechanism at the rigid-flexible synergistic interface. This sizing strategy is also applicable to PPBESK matrices containing biphenyl units and various reinforcement forms (fabrics and short fibers), enabling universal interfacial strengthening and substantial wear-resistance improvement. The concept of Tg-difference-driven dynamic adaptive interfacial design thus provides a water based, environmentally benign, and widely applicable paradigm for high-performance thermoplastic carbon fiber composites.