Effect of Sidewall Fluorination on the Mechanical Properties of Catalytically Grown Multi-Wall Carbon Nanotubes
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Effect of Sidewall Fluorination on the Mechanical Properties of Catalytically Grown MultiWall Carbon Nanotubes Yogeeswaran Ganesan1, Cheng Peng1, Lijie Ci1, Valery Khabashesku2, Pulickel M. Ajayan1 and Jun Lou1 1
Department of Mechanical Engineering and Materials Science, Rice University, 6100 Main Street, Houston, TX, 77006 2 Department of Chemical and Biomolecular Engineering, University of Houston, 4800 Calhoun Road, Houston, Texas, 77004 ABSTRACT We report on the usage of a simple microfabricateddevice, that works in conjunction with a quantitative nanoindenter inside a scanning electron microscope (SEM), for the in situ quantitative tensile testing of individual sidewall fluorinated multi-wall carbon nanotubes (MWNTs). The stress vs. strain curves and the tensile strength values for five fluorinated specimens have been presented and compared to those of pristine MWNT specimens (data reported earlier). The fluorinated specimens were found to deform and fail in a brittle fashion similar to pristine MWNTs. However, sidewall fluorination was found to have considerably degraded the mechanical properties (tensile strength and load bearing capacity) of the MWNTs. INTRODUCTION The preparation, processing, and property tuning of carbon nanotubes (CNTs) reinforced nanocomposites require the dispersion and solubilization of CNTs, which in their pristine form are not soluble in most common organic solvents and water. Chemical modification of carbon nanotubes with functional groups has been found to be an excellent method to promote dispersion (by de-bundling) and also to improve their interaction with a matrix material via hydrogen or covalent bonding. In recent years, several approaches to achieve the functionalization of carbon nanotubes have been developed, in both molecular and supramolecular chemistry. These approaches include defect functionalization[1], covalent functionalization of the side-walls[2], noncovalentexohedral functionalization[3] andendohedral functionalization [4]. Besides a general improvement in the solubility and processibility that can be achieved by all these approaches, sidewall functionalizations are particularly interesting since they significantly alter the structural and electronic properties of carbon nanotubes, yielding new nanotube derivatives with useful properties of their own [5]. However, modifying the nanotubes by sidewall functionalization changes the surface structure since it results in the cleavage of carbon-carbon bonds along the graphite sidewall, therefore degrading their intrinsic mechanical properties. The direct addition of fluorine [5], hydrogen [6], aryl groups [7,8], nitrenes, carbenes, and radicals [9,10]among others, to the side walls of pristine SWNTs have been reported in the past. Fluorination as a covalent functionalization strategy is considered particularly important since it can improve dispersion considerably and because fluorine can be substituted with more complex addends, opening the way to more complex chemical functionalization of nanotubes for
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