Polymer Nanofibers Containing Isolated and Aligned Single Wall Carbon Nanotubes
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0948-B03-05
Polymer Nanofibers Containing Isolated and Aligned Single Wall Carbon Nanotubes Robert Young, Stephen Eichhorn, and Prabhakaran Kannan School of Materials, University of Manchester, Grosvenor Street, Manchester, M1 7HS, United Kingdom
ABSTRACT Electrospinning has been used to prepare poly(vinyl alcohol) (PVA) nanofibers, with diameters ranging from 1 µm down to 20 nm, that contain dispersions of isolated, well-aligned, single wall carbon nanotubes (SWNTs). The nanofibers were characterized by Raman spectroscopy and single radial breathing modes (RBMs) were found for the SWNTs in the nanofibers indicating debundling of the original SWNT ropes. Moreover a split Gí band for some nanotubes and the results of polarized Raman spectroscopy were consistent with the presence of highly aligned and possibly isolated SWNTs along the nanofiber axes. INTRODUCTION It is well established that carbon nanotubes have potentially impressive mechanical properties and it is thought that one of the best ways to realize these properties is to incorporate them in composites [1,2]. The highest levels of stiffness and strength are obtained for composites when the reinforcing fibers are aligned in one direction. It has also been generally recognized that for any nanocomposite to realize its full potential in terms of mechanical properties the nanophase has to be well-dispersed. Hence, the isolation of reinforcing phases and their alignment are critical stages in the development of these potentially useful materials. There have been a number of reports of attempts to prepare polymer fibers containing aligned carbon nanotubes by a variety of different routes such as melt-spinning [3-5] and more recently by electrospinning [6-8] which offers significant potential in the area of nanomanufacturing [9]. Reinforcement of the polymer by the nanotubes has been reported for electrospun fibres [6]. A recent study by Kumar and coworkers [10] reported the preparation by electrospinning of PMMA and PAN nanofibers containing single wall carbon nanotubes. They found that the nanofibers had a core-shell structure with SWNT bundles along the middle of the nanofibers. They also demonstrated that the SWNTs were subjected to a residual compressive stress. A number of techniques, such as transmission electron microscopy (TEM) and Raman spectroscopy, can be employed to characterize the microstructures of nanotube-reinforced fibers. It is difficult to use TEM since the electron density difference between the nanotubes and the polymer matrix is small, leading to poor contrast [6,8]. On the other hand, Raman spectroscopy is a powerful technique capable of giving detailed microstructural information. Attempts have been made to determine the degree of orientation of the nanotubes in a polymer fiber using polarized Raman spectroscopy [3-5,7,8]. It is found for aligned SWNTs [3-5] that the intensity of both the RBMs and the G-band is a maximum when the direction of laser polarization is parallel to the SWNT orientation (fiber) axis and a minimum when it is at
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