Fabrication of a highly hard yet tough epoxy nanocomposite coating by incorporating graphene oxide nanosheets dually modified with amino silane coupling agent and hyperbranched polyester-amide

This study aims to promote the epoxy systems' mechanical attributes (especially toughness) using surface-treated graphene oxide nanosheets. To this end, the graphene oxide nanoplatelets were synthesized and then surface-modified. 3-amino propyl triethoxy silane (APTES) and hyperbranched polyester amide (HBP) were employed via a serial approach. The results of different characterizing techniques (FTIR, TGA, XRD, Raman, and FE-SEM) approved the leading role of dual modification in expanding the inter-layer distance of nanoplatelets and significantly improving the filler dispersion within organic media. All unmodified and variously modified nanosheets were introduced into the epoxy at three loading levels (0.25, 0.5, and 1 wt%). While almost all modified nanoparticles could considerably enhance the hardness and toughness, the highest enhancement (2.6 times in toughness and 2.28 times in micro-hardness) was achieved with 1 wt% graphene oxide sequentially treated with APTES and HBP. Simultaneous promotion of hardness and toughness, which usually have an inverse relationship, was a highly desirable achievement. Our structural studies, utilizing the DMTA technique, revealed that such promotion was indebted to the simultaneous reinforcement in the physical (uniform filler distribution) and chemical (increased crosslinking density without any Tg elevation) aspects of the resultant network.