Fully Atomistic Molecular Dynamics Investigation of the Simplest Model of Dry-Draw Fabrication of Carbon Nanotube Fibers

Macroscopic assemblies of carbon nanotubes (CNTs) are desirable materials because of the excellent CNT properties. Amongst the methods of production of these CNT materials, the dry-draw fabrication where CNT fibers (CNTFs) are directly pulled out from a CNT forest is known to provide good physical properties. Although it is known that vertical alignment of CNT bundles within the CNT forest is important, the mechanisms behind the dry-draw fabrication of CNTFs are still not completely understood. The simplest known dry-draw model consists of CNT bundles laterally interacting by only van der Waals forces (vdWf). Here, by fully atomistic classical molecular dynamics simulations, we show that the simplest dry-draw model does not produce CNTFs. We also show one important condition for a pair of adjacent CNT bundles to connect themselves under vdWf only and discuss why it leads to the failure of the simplest model.Comment: Work presented in the 2022 MRS Fall Meetin

The Structure of Graphene on Graphene/C60/Cu Interfaces: A Molecular Dynamics Study

Two experimental studies reported the spontaneous formation of amorphous and crystalline structures of C60 intercalated between graphene and a substrate. They observed interesting phenomena ranging from reaction between C60 molecules under graphene to graphene sagging between the molecules and control of strain in graphene. Motivated by these works, we performed fully atomistic reactive molecular dynamics simulations to study the formation and thermal stability of graphene wrinkles as well as graphene attachment to and detachment from the substrate when graphene is laid over a previously distributed array of C60 molecules on a copper substrate at different values of temperature. As graphene compresses the C60 molecules against the substrate, and graphene attachment to the substrate between C60s ("C60s" stands for plural of C60) depends on the height of graphene wrinkles, configurations with both frozen and non-frozen C60s structures were investigated in order to verify the experimental result of stable sagged graphene when the distance between C60s is about 4 nm and height of graphene wrinkles is about 0.8 nm. Below the distance of 4 nm between C60s, graphene becomes locally suspended and less strained. We show that this happens when C60s are allowed to deform under the compressive action of graphene. If we keep the C60s frozen, spontaneous "blanketing" of graphene happens only when the distance between them are equal or above 7 nm. Both above results for the existence of stable sagged graphene for C60 distances of 4 or 7 nm are shown to agree with a mechanical model relating the rigidity of graphene to the energy of graphene-substrate adhesion. In particular, this study might help the development of 2D confined nanoreactors that are considered in literature to be the next advanced step on chemical reactions.Comment: 7 pages, 4 figure