Deformation Mechanisms of Very Long Single-Wall Carbon Nanotubes Subject to Compressive Loading

We report atomistic studies of single-wall carbon nanotubes with very large aspect ratios subject to compressive loading. These long tubes display significantly different mechanical behavior than tubes with smaller aspect ratios. We distinguish three different classes of mechanical response to compressive loading. While the deformation mechanism is characterized by buckling of thin shells in nanotubes with small aspect ratios, it is replaced by a rod-like buckling mode above a critical aspect ratio, analogous to the Euler theory in continuum mechanics. For very large aspect ratios, a nanotube is found to behave like a flexible macromolecule which tends to fold due to vdW interactions between different parts of the carbon nanotube. This suggests a shell-rod-wire transition of the mechanical behavior of carbon nanotubes with increasing aspect ratios. While continuum mechanics concepts can be used to describe the first two types of deformation, statistical methods will be necessary to describe the dynamics of wire-like long tubes.

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Self-Folding and Unfolding of Carbon Nanotubes

Journal of Engineering Materials and Technology ◽

10.1115/1.1857938 ◽

2005 ◽

Vol 128 (1) ◽

pp. 3-10 ◽

Cited By ~ 34

Author(s):

Markus J. Buehler ◽

Yong Kong ◽

Huajian Gao ◽

Yonggang Huang

Keyword(s):

Carbon Nanotubes ◽

Critical Temperature ◽

Aspect Ratio ◽

Mechanical Response ◽

Driving Forces ◽

Compressive Loading ◽

Single Wall Carbon Nanotubes ◽

Stable States ◽

Buckling Mode ◽

Aspect Ratios

Carbon nanotubes (CNTs) constitute a prominent example of nanomaterials. In most studies on mechanical properties, the effort was concentrated on CNTs with relatively small aspect ratio of length to diameters. In contrast, CNTs with aspect ratios of several hundred can be produced with today’s experimental techniques. We report atomistic-continuum studies of single-wall carbon nanotubes with very large aspect ratios subject to compressive loading. It was recently shown that these long tubes display significantly different mechanical behavior than tubes with smaller aspect ratios (Buehler, M. J., Kong, Y., and Guo, H., 2004, ASME J. Eng. Mater. Technol. 126, pp. 245–249). We distinguish three different classes of mechanical response to compressive loading. While the deformation mechanism is characterized by buckling of thin shells in nanotubes with small aspect ratios, it is replaced by a rodlike buckling mode above a critical aspect ratio, analogous to the Euler theory in continuum mechanics. For very large aspect ratios, a nanotube is found to behave like a wire that can be deformed in a very flexible manner to various shapes. In this paper, we focus on the properties of such wirelike CNTs. Using atomistic simulations carried out over a several-nanoseconds time span, we observe that wirelike CNTs behave similarly to flexible macromolecules. Our modeling reveals that they can form thermodynamically stable self-folded structures, where different parts of the CNTs attract each other through weak van der Waals (vdW) forces. This self-folded CNT represents a novel structure not described in the literature. There exists a critical length for self-folding of CNTs that depends on the elastic properties of the tube. We observe that CNTs fold below a critical temperature and unfold above another critical temperature. Surprisingly, we observe that self-folded CNTs with very large aspect ratios never unfold until they evaporate. The folding-unfolding transition can be explained by entropic driving forces that dominate over the elastic energy at elevated temperature. These mechanisms are reminiscent of the dynamics of biomolecules, such as proteins. The different stable states of CNTs are finally summarized in a schematic phase diagram of CNTs.

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Charge Transfer Dynamics in Single-Wall Carbon Nanotubes Mat: In Situ Raman Spectroscopy

MRS Proceedings ◽

10.1557/proc-785-d9.3 ◽

2003 ◽

Vol 785 ◽

Author(s):

S. Gupta ◽

M. Hughes ◽

A.H. Windle ◽

J. Robertson

Keyword(s):

Carbon Nanotubes ◽

Raman Spectroscopy ◽

Charge Transfer ◽

Bond Length ◽

Mechanical Response ◽

Radial Breathing Mode ◽

Single Wall Carbon Nanotubes ◽

In Situ Raman Spectroscopy ◽

Single Wall Carbon

ABSTRACTCarbon nanotubes-based actuator has been investigated using in situ Raman spectroscopy in order to understand the actuation mechanism and to determine associated parameters. We built an actuator from a sheet of single-wall carbon nanotubes (SWNT mat) and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. Since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm-1 varies inversely with the nanotube diameter and the G band at ∼1590 cm-1 varies with the axial bond length, the variation of bonding was monitored with potential. In addition, the intensities of both the modes vary with either emptying/depleting or filling of the bonding and antibonding states due to electrochemical charge injection. We discuss the variation of intensity/frequency providing valuable information on the dynamics of charge transfer on the SWNT mat surface. We found the in-plane microscopic strain (∼ -0.25%) and the charge transfer per carbon atom (fc ∼ -0.005) as an upper bound for the electrolytes used. It is demonstrated that though the present analyses does comply with the proposition made earlier, but the quantitative estimates of the associated parameters are significantly lower if compared with those of reported values for carbon nanotubes. Moreover, the extent of variation (i.e. coupled electro-chemo-mechanical response) does depend upon the type of counter-ion used. The cyclic voltammetry (CV) is also described briefly.

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Fuel Cell Applications of Single Wall Carbon Nanotubes

1st International Fuel Cell Science, Engineering and Technology Conference ◽

10.1115/fuelcell2003-1708 ◽

2003 ◽

Author(s):

R. P. Raffaelle ◽

B. Landi ◽

T. Gennett ◽

R. S. Morris ◽

B. Dixon ◽

...

Keyword(s):

Carbon Nanotubes ◽

Fuel Cells ◽

Fuel Cell ◽

Direct Methanol Fuel Cells ◽

Active Material ◽

Pem Fuel Cells ◽

Proton Exchange ◽

Single Wall Carbon Nanotubes ◽

Single Wall Carbon ◽

Aspect Ratios

Novel carbon materials with nanometer dimensions are of potentially significant importance for a number of advanced technological applications. Currently, considerable interest exists in the possible applications of single wall carbon nanotubes (SWNTs) to proton exchange membrane (PEM) fuel cells. Proposed uses include as anode materials in both hydrogen and direct methanol fuel cells, solid polymer electrolyte additives, active cathode materials and bipolar plate interconnects. One of the desirable attributes afforded by the use of SWNTs in fuel cell applications stems from a combination of their extremely high electrical conductivity and large aspect ratios which results in a low weight percent for the electrical percolation threshold. This conductivity combined with the outstanding catalytic surface area offered by these nanostructured materials makes them a potentially outstanding active material for PEM electrodes. In addition, the high thermal conductivity, enhanced mechanical properties and corrosion resistance of polymer-SWNT composites may play a large role in developing new fuel cell designs such as thin-film microelectronic fuel cells. We will review the current applications involving SWNTs in PEM fuel cells and report on the recent work in the Nanopower Research Lab at RIT and it partners on utilizing high purity SWNT’s in microelectronic fuel cells.

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Photovoltaic Devices Based on Single Wall Carbon Nanotubes

MRS Proceedings ◽

10.1557/proc-1210-q04-06 ◽

2009 ◽

Vol 1210 ◽

Author(s):

Zhongrui Li ◽

Viney Saini ◽

Shawn Edward Bourdo ◽

Liqiu Zheng ◽

Enkeleda Dervishi ◽

...

Keyword(s):

Thin Film ◽

Carbon Nanotubes ◽

Solar Cells ◽

Carrier Transport ◽

Single Wall Carbon Nanotubes ◽

Chemical Doping ◽

Single Wall Carbon ◽

Aspect Ratios ◽

Conversion Materials ◽

P Type

AbstractSingle-wall carbon nanotubes (SWNTs) are potentially an attractive material for PV applications due to their many unique structural and electrical properties. SWNTs can be directly configured as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and charge carriers collecting/transport layers. SWNTs can be modified into either p-type conductor through chemical doping (like thionyl chloride, or just exposure to air) or n-type conductor through polymer (like polyethylene imine) functionalization. The solar cells consist of either a semitransparent thin film of p-type nanotubes deposited on an n-type silicon wafer or a semitransparent thin film of n-type SWNT on p-type substrate to create high-density p-n heterojunctions between nanotubes and silicon substrate to favor charge separation and extract electrons and holes. The high aspect ratios and large surface area of nanotubes can be beneficial to exciton dissociation and charge carrier transport thus improving the power conversion efficiency.

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