Collective Behaviour of Vertically Aligned Carbon Nanotubes: from a Single Tube towards Complex Networks
In this chapter we discuss the mechanical behaviour of vertically aligned carbon nanotubes (VACNTs) also known as carbon nanotube (CNT) arrays, bundles, brushes, foams, forests, mats, and turfs. VACNTs are complex, hierarchical structures of intertwined t
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Collective Behaviour of Vertically Aligned Carbon Nanotubes: from a Single Tube towards Complex Networks Siddhartha Pathak
Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
8.1. Definition In this chapter we discuss the mechanical behaviour of vertically aligned carbon nanotubes (VACNTs) also known as carbon nanotube (CNT) arrays, bundles, brushes, foams, forests, mats, and turfs. VACNTs are complex, hierarchical structures of intertwined tubes arrayed in a nominally vertical alignment due to their perpendicular growth from a stiff substrate. They are a unique class of materials having many of the desirable thermal, electrical, and mechanical properties of individual carbon nanotubes, while exhibiting these properties through the collective interaction of thousands of tubes on a macroscopic scale.
8.2. Introduction While individual CNTs have been announced as the strongest material known (Treacy et al. 1996) and have shown extremely high strength and Young’s modulus in tensile tests on individual tubes (Treacy et al. 1996, Min-Feng et al. 2000), VACNTs are more likely to find use in applications requiring large compliance and deformability (Cao et al. 2005, Gogotsi 2006). Examples of these include microelectromechanical systems (MEMS) and impact mitigation/energy absorption, where they are promising candidates for their multifunctional nature, wide ranging thermal stability, well-defined large surface area, and relative ease of manufacture (Cao et al. 2005). A proper understanding of the collective mechanical behaviour of these structures, especially instabilities leading to buckling and inhomogeneity’s which weaken mechanical performance, is thus of great importance for their design and success in these and other future applications. VACNTs are distinct from other CNT structures (Salvetat et al. 2006) in that the tubes that make up the material grow perpendicularly to the support substrate, making them nominally vertically aligned. An important characteristic all VACNTs share is that the tubes themselves are long enough to become intertwined with each other during the growth process, leading to a highly complex and hierarchical O. Paris (Ed.), Structure and Multiscale Mechanics of Carbon Nanomaterials, CISM International Centre for Mechanical Sciences DOI 10.1007/ 978-3-7091-1887-0_8 © CISM Udine 2016
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microstructure with distinct organizational details at different magnification levels. This is in contrast to arrays of vertically aligned CNTs that are short and/or sparse enough that each CNT stands alone (Waters et al. 2004, Waters et al. 2005). Figure 8.1 show the complex hierarchical nature of the VACNT microstructure with their Indent on sample bulk
141.5 μm
Indents on sample edge
(a)
VACNT Si Substrate
100 μm
1 μm
(b)
5 nm
(c)
200 nm
Figure 8.1. SEM images reveal the hierarchical morphology of the (a) 141.5 μm thick VACNT films (magnification 260X), which consist of (b) nominally vertical aligned CNTs visible at a lower magnificati
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