Making Massive Crowds of Nanotubes: Growth Mechanisms, Microstructures, and Composite Materials

Professor John A. Hart,
Assistant Professor,
Department of Mechanical Engineering,
University of Michigan

ABSTRACT:
While carbon nanotubes (CNTs) have been produced industrially in ton-scale quantities for nearly two decades, scalable manufacturing processes which precisely control the structure, length, and alignment of CNTs are needed to realize the exceptional properties of CNTs at larger scales. I will discuss CNT synthesis by atmospheric-pressure thermal chemical vapor deposition, where chemical, thermal, and mechanical reactions control facilitates growth of millimeter-tall aligned CNT “forests” as uniform films, and two- or three-dimensionally shaped microstructures. By engineering the catalyst coarsening process, we tune CNT diameter from 6–24nm, and correspondingly adjust the areal density. Using in situ and ex situ X-ray scattering and real-time kinetics measurements, we map structural variations within CNT forests and elucidate mechanisms of self-organization and growth termination.

Capillary interactions between aligned CNTs and polymers facilitate direct fabrication of ordered composites; CNT/SU-8 microprobes show a 200% Young’s Modulus increase at 2% CNT loading, and carbon fiber specimens exhibit 300% higher Mode I toughness when reinforced using interlaminar CNT forests. Post-growth densification and infiltration of CNT structures shows promise to fabricate solid-like CNT ribbons and beams for applications including micromechanical structures and flexible electronics.

BIO:
John Hart is Assistant Professor of Mechanical Engineering at the University of Michigan; he joined the faculty in September 2007. John holds Ph.D. (2006) and S.M. (2002) degrees from the Massachusetts Institute of Technology, and a B.S.E (2000) degree from the University of Michigan, all in Mechanical Engineering. He received the 2006 MIT Senturia Prize for best doctoral thesis in micro/nano technology, and graduate fellowships from the Fannie and John Hertz Foundation, National Science Foundation, and MIT Martin Foundation. John's research currently focuses on synthesis and applications of nanostructured materials, microsystems, mechanical design, and scientific visualizations.