title: Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth.
abstract: The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.
authors.affiliation: Department of Mechanical Engineering and Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|School of Engineering, Indian Institute of Technology Mandi , Mandi, Himachal Pradesh 175001, India.
authors.forename: Viswanath
authors.initials: V
authors.lastname: Balakrishnan
authors.affiliation: Department of Mechanical Engineering and Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|Department of Mechanical Engineering, University of Michigan , 2350 Hayward Street, Ann Arbor, Michigan 48109, United States.|Department of Industrial Engineering, University of Pittsburgh , 3700 O'Hara Street, Pittsburgh, Pennsylvania 15261, United States.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Bedewy
authors.affiliation: Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory , Livermore, California 94550, United States.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Meshot
authors.affiliation: Department of Mechanical Engineering and Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Sebastian W
authors.initials: SW
authors.lastname: Pattinson
authors.affiliation: Department of Mechanical Engineering, University of Michigan , 2350 Hayward Street, Ann Arbor, Michigan 48109, United States.
authors.forename: Erik S
authors.initials: ES
authors.lastname: Polsen
authors.affiliation: Department of Mechanical Engineering, University of Michigan , 2350 Hayward Street, Ann Arbor, Michigan 48109, United States.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Laye
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Dmitri N
authors.initials: DN
authors.lastname: Zakharov
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Stach
authors.affiliation: Department of Mechanical Engineering and Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: A John
authors.identifier: 0000-0002-7372-3512
authors.initials: AJ
authors.lastname: Hart
keywords: carbon nanotubes; chemical vapor deposition; electron microscopy; forces; self-organization