Applying alternating “rigid-and-soft” interphase into functionalized graphene oxide/epoxy nanocomposites toward enhanced mechanical properties

The interphase structure plays a significant role in the interfacial interactions and mechanical properties of epoxy-based nanocomposites. Inspired by the nacre’s structure, a “rigid-and-soft” multilayer interphase was constructed between functionalized graphene oxide (GO) and epoxy matrix through grafting rigid polydopamine (PDA) and flexible polyetheramine D230 alternatively on GO surfaces. The structural and morphological characteristics of modified GO (MGO) with various numbers of grafted layers were characterized. The dispersion of MGO in epoxy matrix was investigated. The mechanical properties of nanocomposites at room temperature (RT) and liquid nitrogen temperature (LNT) were evaluated. MGO with three layers of PDA/D230 (MGO-L3) endowed the nanocomposites with the highest mechanical properties, owing to the “rigid-and-soft” interphase which can synergistically enhance the stress transfer and accelerate the energy dissipation. At RT, nanocomposites showed the maximum increment of 25.8% in tensile strength and 13.0% in elongation at break compared to neat epoxy. At LNT, the corresponding increments could reach 6.8% and 23.1%, respectively. The influence of the “rigid-and-soft” interphase on the mechanical properties of MGO/epoxy nanocomposites under thermal cycling were investigated as well. Based on the fracture morphology, the toughening mechanisms of MGO at RT and LNT were both disclosed.