Transmission Electron Microscopy of
Polymer-Functionalized Carbon Nanotubes
J. Doe1, V.R. Famous2 and A.N.D. Rich1
1Department of Affiliation, Best University, 1111 Main Street, City, ON, L8A 4X7, Canada
2Department of Acconting, Poor University, 9999 Second Street, Smalltown, ON, M2A 5Y1, Canada
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Paragraphs are separated by an empty line. One of the factors limiting the application of carbon nanotubes is that they are not soluble in their raw state. Since solubility is required to improve carbon nanotubes processing and manipulation for uses in structural and electronic applications, there have been significant efforts to address this important issue. It has been recently shown [1] that carbon nanotubes can be functionalized so that they become soluble in selected solvents by covalent grafting of soluble molecules and polymers on their surface. These “polymer-functionalized carbon nanotubes” can also be mixed with bulk polymers to form a covalently bonded composite material that does not exhibit phase separation between the polymers and the carbon nanotubes.
The objective of this study was to use the transmission electron microscopy (TEM) to support the development of new synthesis routes to produce polymer-functionalized carbon nanotubes and polymer-nanotube composite thin films. In this study we explored the effect of varying the molecular weight of the attached polymer, and the orientation of the nanotubes within the polymer-nanotube composite thin films. TEM observations proved essential for providing evidence of the functionalization chemistry and to gain insight into the effects that polymer-functionalized carbon nanotubes have on bulk polymer thin films.
With increases in the molecular weight of the polymer chains grafted to the nanotubes, the visibility of nanotubes in the TEM specimen greatly reduced. Occasionally single carbon nanotubes or small bundle of nanotubes were found protruding out into free space from the edge of the polymer (figure 1). Such lone nanotubes do not appear to be entirely surrounded by the polymer around the protruding portion of the nanotubes although it is clearly possible to see that their surfaces are not as smooth as raw nanotubes. In thin areas of samples it was also possible to resolve the polymer-functionalized carbon nanotubes when fully surrounded by the polymer.
Polymer-nanotube composite thin films were also prepared by the addition of polymer-functionalized carbon nanotubes to a bulk polystyrene thin film. We made use of the fact that the electron beam from the TEM often caused the polymer-nanotube composite thin film to exhibit crazing, which led to film cracking. Cracking involved the destruction of fibrillar bridges that hold two sides of a craze together. Our observations indicate a potential correlation between the presence of nanotubes in the film and the location of the fibrillar bridges. Since carbon nanotubes have an extremely high tensile strength in their axial direction, these results suggest that, if nanotubes are oriented axially in a fibrillar bridge, they may help to prevent or slow down the cracking of a craze caused by a tensile stress perpendicular to the crack direction[2]
References:
1. N. Author, S. Someone, and A. Person, J. Am. Chem. Soc., (2010) 123, 2345-2355.
2. This work was carried out with funding from NSERC. The authors acknowledge valuable discussions with X.Y.Name and experimental work from A.B. Person.
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