Magnetically processed carbon nanotube/epoxy nanocomposites: Morphology, thermal, and mechanical properties Mohamed Abdalla a , Derrick Dean a, * , Merlin Theodore b, c , Jennifer Fielding c , Elijah Nyairo d , Gary Price e a University of Alabama at Birmingham, Department of Materials Science and Engineering,1530 3rd Avenue, South, Birmingham, AL 35294-4461, USA b Universal Technology Corporation, Dayton, OH 45434, USA c AFRL, Materials & Manufacturing Directorate, Hybrids and Composites Branch, WPAFB, OH 45433, USA d Alabama State University, Department of Physical Science, Montgomery, AL 36101, USA e University of Dayton Research Institute, 300 College Park Dr, Dayton OH 45469, USA article info Article history: Received 16 February 2009 Received in revised form 1 May 2009 Accepted 19 May 2009 Available online 6 June 2009 Keywords: Carbon nanotubes Epoxy nanocomposite Magnetic alignment abstract The processing-structure–property relationships of multiwalled carbon nanotubes (MWNTs)/epoxy nanocomposites processed with a magnetic field have been studied. Samples were prepared by dispersing the nanotube in the epoxy and curing under an applied magnetic field. The nanocomposite morphology was characterized with Raman spectroscopy and wide angle X-ray scattering, and correlated with thermo-mechanical properties. The modulus parallel to the alignment direction, as measured by dynamic mechanical analysis, showed significant anisotropy, with a 72% increase over the neat resin, and a 24% increase over the sample tested perpendicular to the alignment direction. A modest enhancement in the coefficient of thermal expansion (CTE) parallel to the alignment direction was also observed. These enhancements were achieved even though the nanotubes were not fully aligned, as determined by Raman spectroscopy. The partial nanotube alignment is attributed to resin a gel time that is faster than the nanotube orientation dynamics. Thermal conductivity results are also presented. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Since the discovery of carbon nanotubes (CNTs), polymer/CNT nanocomposites have attracted tremendous attention in both academic and industrial research laboratories [1–17]. The intense interest in these materials stems from the fact that carbon nanotubes possess excellent mechanical properties, good electrical and thermal conductivity [2–17]. Potential applications of polymer/CNT nano- composites include: energy storage and energy conversion devices, sensors, field emission displays, radiation sources, hydrogen media, nanometer-sized semi-conductor devices, probes, interconnects, coatings, encapsulates, structural materials, and others [2,3,15]. Several studies have focused on the fabrication and character- ization of CNT/polymer nanocomposites [9,18–23]. These studies have shown that randomly oriented CNTs embedded in polymer matrices have failed to generate composites in which the full potential of superior properties of the CNTs can be exploited [24]. The final composite properties hinge on variables such as CNT dispersion, concentration, aspect ratio and orientation. A homo- geneous dispersion of the CNTs in the polymer matrix is essential to obtain uniform properties and efficient load transfer during most applications. Good dispersion is usually hindered by the tendency of CNTs to aggregate as a result of Van der Waals attractions. CNT concentration and aspect ratio determines how easily CNTs can interact with each other to build an interconnecting network that can transfer heat and electrons to enhance the thermal and elec- trical properties of the nanocomposite. The degree of alignment of the CNTs has a profound effect on the mechanical properties especially when the composite is loaded parallel or perpendicular to the CNT orientation direction. The alignment process can also potentially provide a conductive pathway for electrons and phonons which will improve electrical and thermal properties. Carbon nanotubes have been aligned in polymer matrices using different approaches such as melt processing [13,25–27], DC plasma-assisted hot filament chemical vapor deposition process [28], mechanical stretching [29], application of magnetic and electric fields [30–34,35], and electrospinning. In our laboratory, we have employed mechanical shearing to orient CNTs in an epoxy resin matrix, followed by curing at elevated temperatures [36]. Dynamic mechanical analysis (DMA) showed significant anisotropy in the modulus. It was postulated that curing at elevated temperature after shearing lowered the resin viscosity and resulted in a much faster relaxation of the CNT orientation [37]. Consequently, a significant but unknown fraction of the mechanical * Corresponding author. Tel.: þ1 205 975 4666; fax: þ1 205 934 8485. E-mail address: deand@uab.edu (D. Dean). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2009.05.059 Polymer 51 (2010) 1614–1620