A rigid-and-flexible interphase was established by a starlike copolymer (Pc-PGMA/Pc) consisting of one tetraaminophthalocyanine (TAPc) core with four TAPc-difunctionalized poly­(glycidyl methacrylate) (PGMA) arms through the surface modification of carbon fibers (CFs) and compared with various interphases constructed by TAPc and TAPc-connected PGMA (Pc-PGMA). The increase in the content of N–CO showed that PGMA/Pc branches were successfully attached onto the CF-(Pc-PGMA/Pc) surface, exhibiting concavo-convex microstructures with the highest roughness. Through adhesive force spectroscopy by atomic force microscopy (AFM) with peak force quantitative nanomechanical mapping (PF-QNM) mode and visualization of the relative distribution of TAPc/PGMA via a Raman spectrometer, a rigid interphase with highly cross-linked TAPc and a flexible layer from PGMA arms as the soft segment were separately detected in CF-TAPc/EP and CF-(Pc-PGMA)/EP composites. The rigid-and-flexible interphase in the CF-(Pc-PGMA/Pc)/EP composite provided excellent stress-transfer capability by the rigid inner modulus intermediate layer and energy absorption efficiency from the flexible outer layer, which contributed to 64.6 and 61.8% increment of transverse fiber bundle test (TFBT) strength, and 33.8 and 40.6% enhancement in interfacial shear strength (IFSS) in comparison with those of CF-TAPc/EP and CF-(Pc-PGMA)/EP composites. Accordingly, schematic models of the interphase reinforcing mechanism were proposed. The interfacial failures in CF-TAPc/EP and CF-(Pc-PGMA)/EP composites were derived from the rigid interphase without effective relaxation of interfacial stress and soft interphase with excessive fiber–matrix interface slippage, respectively. The cohesive failure in the CF-(Pc-PGMA/Pc)/EP composite was attributed to the crack deflection through the balance of the modulus and deformability from the twin-stage gradient intermediate layer.

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Thermally reduced graphene oxide–polyamide (TrGO‐PA) hybrids were fabricated by self‐assembly between TrGO nanosheets and PA microparticles, and the dispersibility, interphase extension, and thermal conduction mechanism of TrGO‐PA/epoxy (EP) composites were investigated. Most of the oxygen‐containing functional groups of TrGO were removed, and a conjugated structure of graphene was recovered. TrGO was distributed evenly on the PA surface via electrostatic adsorption between TrGO and PA, which resulted in the inhibition of TrGO aggregation in the epoxy matrix. Compared with that of TrGO/EP and PA/EP composites, the thermal interface resistance (RTIM) of TrGO‐PA/EP composites was greatly decreased to 38.3 mm2 kW−1 and the thermal conductivity was improved to 0.268 W/(m K), which was attributed to the enhanced dispersibility of TrGO‐PA and the enlarged interphase in TrGO‐PA/EP composites. A schematic model of thermal conduction mechanisms was proposed based on the formation of contiguous thermal transfer pathways by bridged TrGO adsorbed on well‐dispersed PA microparticles in TrGO‐PA/EP composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47826.

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Amino-terminated naphthalimide (NDI) with ultraviolet (UV) absorptivity was synthesized to sizing on poly(p-phenylene benzobisoxazole) (PBO) fiber surface, and UV aging resistance PBO fiber and interfacial adhesion of their composites was investigated. Compared with pristine PBO fiber, the surface chemical activity and roughness of NDI-PBO fiber were increased. In comparison with pristine PBO fiber, tensile strength, intrinsic viscosity ([η]), and diameter of NDI-PBO fiber showed a better retention, and the enhanced UV-aging resistance was verified by hardly visible macroscopic defects on NDI-PBO fiber. Meanwhile, transverse fiber bundle test strength of NDI-PBO fiber composites was promoted by stronger mechanical interlocking and chemical interaction. The synergistic improvement in UV aging resistance and interfacial adhesion of PBO fiber was attributed to undamaged crystal and molecular structure from UV protection effects of NDI layer and strong chemical bonding between reactive groups of NDI and epoxy matrix.