Studies On The Interface Design And Mechanical Propertiesof Collagen-Mimic Carbon Nanotube Bundles

Weak interface has been a long-standing bottleneck critically hindering the exploitation of the ultra-high stiffness and strength of carbon nanotubes(CNTs)as reinforcement materials.Inspired by the structure of collagen fibril,we proposed a covalently cross-linked interface design for ultra-strong CNT bundles.In our studies,molecular dynamics simulations together with theoretical modeling were conducted to systematically study the load-transfer capacity and failure behaviors of the crosslinked interface,including the influence of crosslink type,length,density,interface length and distribution pattern.We found that a small number of covalent crosslinks can significantly enhance the interface stiffness and strength.The shorter crosslinks usually yield higher interface stiffness while the longer crosslinks generally produce higher interface strength.There are three major failure modes unveiled as the crosslink density and interface length vary,namely the abrupt interface failure,the gradual interface failure and the CNT break.A forth failure mode was also seen upon an optimal interface design,in which bond breaks propagate simultaneously and gradually in crosslinked interfaces and CNTs and consequently the interface strength and toughness are both maximized at the same time.To characterize the mechanical behaviors of the interface of uniformly distributed crosslinks,a theoretical model based on the theories of elasticity and facture mechanics was developed,and several principles and guidelines were drawn upon the optimization of crosslinked interface design.Furthermore,three distribution patterns of crosslinks,i.e.,the uniform distribution,two-end distribution and central distributionwere investigated and their enhancing effect in the interface properties were compared.It is found that the two-end distribution has an advantage in increasing the interface stiffness and strength,while the central distribution is superior in improving the interface ductility.Carbon nanotubes are regarded as a promising reinforcement material due to their extraordinary mechanical properties,and high-performance carbon nanotube fibers have great potential applications in advanced composites.The studies and findings here provide useful insights into the novel interface design of high-performance CNT fibers.