Correlation between interfacial molecular structure and mechanics in CNT/epoxy nano-composites

We study the effect of the molecular nature of the interface between an epoxy matrix and multi-walled carbon nanotubes (CNTs) on the mechanical properties of the resultant nano-composites, with emphasis on toughness. A number of samples based on variously functionalized CNTs, namely, pristine, carboxylated, and aminated CNTs are examined, with different qualities of dispersion. Nano-composite toughness is found to increase with enhanced interfacial adhesion, an effect that is opposite to what is usually observed in traditional fiber-based composites. The classical pull-out energy model is shown to effectively explain this result. It is thus possible to tune the toughness of a nano-composite by adjusting the molecular nature of its interface and the CNT characteristics, namely its strength and its length relative to its critical length.