291595 Understanding Single-Walled Carbon Nanotube Growth Through Reactive Molecular Dynamics Simulations

Monday, October 29, 2012
Hall B (Convention Center )
Jenni Beetge, Chemical Engineering, Texas A&M University, Pearland, TX

Abstract for AIChE poster presentation

Understanding single-walled carbon nanotube growth through reactive molecular dynamics simulations

Jenni Beetge,1 Diego A. Gomez-Gualdron,1,2 and Perla B. Balbuena1,2

1Department of Chemical Engineering, 2Materials Science and Engineering Program,

Texas A&M University, College Station, TX 77843

Single walled carbon nanotubes (SWCNTs) are in high demand due to their exceptional properties, and wide range of applications. However, many applications are reserved for specific  chiralities  because of the difference in properties associated with the twisting of the structure. Currently there are conflicting theories regarding the synthesis mechanism of SWCNT’s. Understanding the effects of key parameters of SWCNT growth during chemical vapor deposition may enable manipulation of the process to produce SWCNTs with  desired chiralities. In such process, a C-containing precursor gas is decomposed over a metal nanocatalyst at a high temperature. This research poster presents the results of classical reactive molecular dynamics (MD) modeling of SWCNT nucleation and growth, focusing on the effects of nanocatalyst-support interaction and precursor type on the nanoparticle state, and nanotube chirality. Using SIMCAT, a reactive  MD algorithm  developed in our group, simulations are run for two types of precursor gases, each with five different metal/support interaction energies, for three nanoparticle sizes. The simulation results are used to visually examine the nucleation and growth processes as well as quantitatively determine statistics regarding the formation and dynamics of carbon species inside and on the nanoparticle surface. The visualization results reflect the combined effect of kinetic barriers and thermodynamic driving forces that cause surface diffusion to dominate after bulk diffusion allowed carbon atoms to fill the inner core of the nanoparticle. From the results we were also able to determine the probability curves and charts of carbon chain formation inside, and on the nanoparticle surface, as well as formation of hexagonal, pentagonal, and heptagonal rings in the nanotube structure.  This latter analysis is used as an indicative of the quality of the growing nanotube. Despite the stabilization of a metal-carbon core, our results did not reflect carbide formation, which is one mechanism under debate. On the other hand, this study shows that the nanoparticle displays a viscous solid behavior, with the solid character depending on the metal/support interaction, and the stage of nanotube growth.

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