Tailored rigid-flexible interphase of M40X composites via block copolymers: A combined method of experimental analysis and molecular dynamic simulation

The rigid-flexible interphase was constructed by polyamide acid-polyether amine block copolymer with various ratios of rigid/flexible segments (PAE(20), PAE(10), PAE(5)), and the correlation of rigid/flexible proportion with interfacial properties of M40X composites was explored via the combined method of experiments and molecular dynamic (MD) simulation. As the proportion of flexible segments increased, the PAE-CF surface exhibited improved chemical activity and uniform coverage. The interfacial simulation presented a distribution plateau of rigid backbones in the interphase of PAE(10)-CF/EP composite, corresponding to the experimentally-verified double transit-modulus platform, which indicated that the spatial homogeneity of the stable crosslinked networks facilitated the gradient interphase stiffening. The graduated interfacial structures contributed to 55.25%, 179.31% increment of simulated interfacial shear stress (ISS), and 7.96%, 19.03% enhancement in interfacial shear strength (IFSS) in comparison with those of PAE(20)-CF/EP and PAE(5)-CF/EP composites. The interphase reinforcing mechanisms were investigated by interfacial residual stress and toughness via experimental analysis and theoretical calculation. Compared with the pristine CF composite, the interfacial residual stress and interfacial toughness were improved by 26.4% and 165.6% in PAE(10)-CF/EP composite, respectively. The integration of stress transfer capacity with energy dissipation efficiency was achieved by the optimal rigid/flexible ratio, which contributed to the balance between the interfacial stiffness and toughness of M40X composites.