Do Nickel and Iron Catalyst Nanoparticles affect the Mechanical Strength of Carbon Nanotubes?

The growth of carbon nanotubes (CNTs) is strongly mediated by the interaction between Carbon atoms and catalyst nanoparticles, in particular in processes like chemical vapor deposition or floating method. However, the effects these nanoparticles on the mechanical strength of the grown CNTs have remained elusive. Using molecular dynamics dynamic simulations via ReaxFF force fields, the interactions between defect-free single wall CNTs and a series of Nickel (Ni) and Iron (Fe) nanoparticles (NPs) are studied. Pure metal NPs significantly reduce the strength of the CNTs whereas oxidized NPs have more limited detrimental effects. If you want to know more, have a look at our publication in Extreme Mechanics Letters.  These movies show the failure of SWCNTs when loaded in tension and in the presence of a Nickel and Iron nanoparticles.

Failure of two 5,5 CNTs in the presence of a Ni nanoparticle
Failure of two 5,5 CNTs in the presence of a Fe nanoparticle

Weakening effect of nickel catalyst particles on the mechanical strength of the carbon nanotube/carbon fiber junction

Engineering the properties of the interface between the fibers and the polymer matrix to further improve the strength of this material remains an ongoing challenge. The direct growth of carbon nanotubes on the carbon fiber surface is a promising way to mitigate the stress concentration around the fibers but would require a strong adhesion between the tubes and the surface. Yet, this property remains largely unknown as the interactions between the surface, the metal nanoparticle catalyst needed to initiate the growth of the tubes and the tubes have not been characterized. Therefore, three- component systems composed of a single wall carbon nanotube (SWCNT), a metal-nanoparticle catalyst (NP) and graphene layers to model a carbon fiber surface have been considered. Reactive molecular dynamics simulations have been performed to predict the adhesion between these three components. Pure nickel and nickel oxide nanoparticle catalysts were modelled and CNTs from bottom- and tip-growth modes were implemented. The atomistic systems were then loaded in tension and the Young’s modulus, strain and stress at failure calculated. A detailed analysis of the formation and breakage of chemical bonds between the carbon, oxygen, and nickel atoms during the tensile tests permitted to obtain a detailed insight of the failure mechanisms. A paper describing in detail this study can be found here.

Failure of a graphene/CNT junction without nanoparticle
Failure of a graphene/CNT junction with a Ni nanoparticle, bottom-growth mode
Failure of a graphene/CNT junction with a NiO nanoparticle, bottom-growth mode