Magnetic Alignment of Carbon Nanofibers in Polymer Composites
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Magnetic Alignment of Carbon Nanofibers in Polymer Composites Donglu Shi, Peng He, Jie Lian1, Xavier Chaud2, Eric Beaugnon2, Lumin Wang1, Rodney C. Ewing1and Robert Tournier2 Dept. of Chemical and Materials Engineering, University of Cincinnati Cincinnati, OH 45221 1 Dept. of Nuclear Engineering and Radiological Science, University of Michigan Ann Arbor, MI 48109 2 Consortium de Recherches pour l’Emergence de Technologies Avancées, CNRS, BP 166, F-38042 Grenoble Cedex 9, France ABSTRACT Carbon nanofibers were well aligned in polymer composite magnetically at moderate fields up to 3 T. Due to the NiO-coating, carbon nanofibers exhibited strong magnetic moments that lead to alignment. Both TEM and SEM results showed the wellaligned nano-fibers in a polymer matrix. Mechanical testing showed a pronounced anisotropy in tensile strength in directions normal (12.1MPa) and parallel (22MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO on the nano fiber surface is discussed.
INTRODUCTION One of the current research topics on nanomaterials has been the development of carbon nanotubes/nano-fibers in polymer composites with optimum properties [1-10]. For both a fundamental understanding of the properties of nanotubes and engineering applications, it requires that the nanotubes and nanofibers in the polymer matrix can be orientated for certain specific properties. Previous researchers have mainly focused their efforts on single-walled carbon nanotubes (SWCNT) due to their considerable magnetic susceptibility that results from the presence of catalyst elements, such as nickel and cobalt [11-14]. For carbon nano-fibers, there have not been any results reported from magnetic alignment as a result of non-magnetic properties of these materials. Attempts have been made to align nanotubes in polymers by mechanical straining [15]. However, only partial alignment was achieved on the surfaces of the sample. Therefore, it is of great interest to develop new techniques to align a small fraction of nanofibers or multiwalled carbon nanotubes (MWCNT) in polymer composites. In nanofiber reinforced polymer composites, the small fraction of nanofibers in the composite matrix must be well dispersed. This issue has been recently dealt with by the authors using a unique plasma polymerization method [16-21]. The alignment of the nanofibers along a specified direction can further result in enhanced mechanical and other physical properties. Due to extremely low magnetic susceptibility of carbon nanofibers (~10-6 emu), the dipole moments induced in the magnetic field are insufficient to cause them to rotate in a viscous liquid and align themselves along the direction of the applied
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field, even at a high field strength. Therefore novel approaches are needed to magnetically align the nano-fibers in bulk polymer composites. We present experimental data on the magnetically aligned carbon nanofibers in polystyrene composites. As a result o
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