Coiled carbon nanotubes: Synthesis and their potential applications in advanced composite structures

Since the discovery of carbon nanotubes, their applications benefit to a wide range of engineering, applied physics and biomaterials areas, because of their superior mechanical and electrical properties. In the advanced composite society, substantial works including the synthesis of different types of nanotubes, manufacturing process of nanotube-related composites, mechanical characterizations of these composites, have been conducted in the past few years. One of the major focuses, has not yet been solved, is on how to ensure a good bonding between straight nanotubes and their surrounding matrix, and also the integrity of the nanotubes' structures, in their atomic scale level after being bonded with the matrix. Physical nanotube pullout and push in tests can be used to determine the interfacial bonding properties of the nanotube/polymer composites. However, due to their size constraint, it is impossible to precisely conduct such tests, based on current testing technology. Although molecular dynamics (MD) simulations are another alternative to roughly estimate the bonding behaviour of the composites, the results are highly dependent on the basic assumptions applied to models. Recently, the development of coiled carbon nanotubes opens a new alternative to reinforce the traditional composites. The coiled configuration of the nanotubes can enhance the fracture toughness as well as mechanical strength of the composites even there is no direct chemical bonding between the nanotubes and matrix. Their coiled shape induces mechanical interlocking when the composites are subjected to loading. In this paper, a critical review on the synthesis of the coiled nanotubes and their applications in advanced composites is given.