Nanodiamond nanocluster-decorated graphene oxide/epoxy nanocomposites with enhanced mechanical behavior and thermal stability

Novel hybrid fillers composed of nanodiamond (ND) nanocluster-decorated graphene oxide (GO) were fabricated and incorporated in an epoxy matrix using a facile thermoregulatory liquid-liquid extraction method. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analyses confirmed a chemical bonding between the (3-aminopropyl)triethoxysilane-functionalized ND and (3-glycidyloxypropyl)trimethoxysilane-functionalized GO. The morphology of the hybrid filler (GN) was characterized by field-emission transmission electron microscopy. ND nanoclusters with an average diameter of 50-100 nm were uniformly grown on the GO surface. The hybrid filler provided significant enhancement of mechanical properties, such as flexural strength, flexural modulus, and fracture toughness. In particular, the epoxy composite containing 0.1 wt% of GN hybrid exhibited a stronger mechanical behavior compared to that containing 0.2 wt% of GO. As the GN loading increased, the thermal stability, the integral procedural decomposition temperature, and the activation energy increased as well. The toughening mechanism was illustrated by a microcrack theory based on the microscopic analysis of the fracture surfaces. The presence of ND nanoclusters not only hindered the aggregation of the GO sheets, but also played a crack pinning role in the polymer-matrix composites, which could significantly enhance its fracture toughness.