An Investigation of Mechanisms Limiting the Growth of Nanotubes for Structural Applications
Abstract
High performance structural materials for a broad range of the Navy applications can greatly benefit from carbon nanotubes (CNT) reinforcement. For all applications, production of quality CNT (MWNT and SWNT, multi- and single-wall CNT) is a prerequisite. In contrast to electronics, where nanotube chirality—the definitive helical symmetry—controls the band gap, for mechanical-structural performance the chirality is less important, and the key is the robust growth of long and defectless filaments. Laboratory growth methods, notably chemical vapor deposition (CVD), have now advanced to producing macroscopic areas of two-dimensional arrays-carpets. Yet the atomistic mechanisms limiting this growth, quality and especially length, remain largely unknown. We will investigate theoretically the key stages in CNT formation and focus on termination of growth, which determines the length of the tubes and whose importance is greatly overlooked. We will now build on nanoreactor (NR) energy diagrams approach, augmented with full DFT computations or a jellium-representation (Je) of the catalyst, in order to: (i) determine NR energy diagrams and the carbon chemical potential range avoiding encapsulation of the catalyst, (ii) assess the NR states of topological defects causing tube detachment from the catalyst, including the dopant/contamination effects, (iii) explore the role of lateral tube-tube traction and how this changes the NR states and controls the cooperative growth. (iv) Importantly, new hypothesis of the mesoscopic gating, modulation of C insertions at the edge by the larger-scale of CNT dynamics, is put forward and will be carefully investigated as intrinsic cause of growth slowdown. A combination of methods will be used in this project, especially the developed in recent years NR diagrams that allow one to organize DFT computational data in a visual and insightful way. Classical MD simulations using the developed force-fields will be also employed, to detect the key candidate steps in carbon evolution from feedstock to the sp2-tube extension. These detailed calculations will supply actual values to the kinetic models to represent the intimate processes of sustained nanotube self-assembly, and suggest the ways to increasing growth efficiency and uninterrupted length, paving the way to the envisioned continuous grown-lengths-into-spinning technology (beyond the fibers produced from relatively short CNT segments).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512251
Entities
People
- Boris I Yakobson
Organizations
- Office of Naval Research
- Rice University
- United States Navy