National Aeronautics and Space Administration
Date of this Version
2012
Citation
Phys. Status Solidi RRL 6, No. 8, 349–351 (2012) / DOI 10.1002/pssr.201206271
Abstract
Polymer nanocomposites filled with one-dimensional (1D) carbon based nanostructures are potential candidates for aerospace applications [1]. In particular, single wall carbon nanotubes (SWCNTs) have advantages over conventional reinforcement materials, like carbon fiber, because of their unique properties [2]. There are several factors to take into consideration in order to optimize the nanocomposite electrical, mechanical and thermal properties. One is the ability to homogeneously disperse the nanotubes into the polymeric material. This has been proved to play an important role to improve each one of the previous mentioned nanocomposite properties [2]. For instance, the interface between the nanotubes and polymer matrix is optimized if the nanotubes are well dispersed, which improves the mechanical response of the nanocomposite. In contrast, nanotubes dispersed as aggregates in the polymer matrix will diminish the interaction at the interface [3]. In the case of electrical properties, although dispersion is important, the major control has to be focused on a reliable method to identify an abundance of metallic/ semiconducting type of nanotubes through chirality [4].
Transmission electron microscopy (TEM) is a technique regularly used to characterize the dispersion of nanofillers in a polymeric matrix. However, imaging SWCNTs in a polymer matrix is challenging due to both its small size (typical diameter ~10 Å) and that its contrast is covered by scattering from the polymer matrix. In this work, we are using modeling results based on high resolution TEM (HRTEM) imaging and electron diffraction (ED) for a deeper analysis of polymer nanocomposites. The implications of our results on the dispersion of SWCNTS in a polymer matrix, as well as chirality determination will be discussed.
Molecular dynamics (MD) was used to simulate SWCNTs and their corresponding interactions with a polyethylene (PE) matrix. The interactions between atoms were calculated using an adaptive intermolecular reactive empirical bond-order (AIREBO) potential, coupled to a longrange Lennard–Jones potential [5]. With a rescale thermostat to control temperature, the equations of motion were integrated with a time step of 0.5 fs at 300 K. Ideal SWCNT configuration was first generated with the graphitic C–C bond length of 1.42 Å. A nanotube diameter of d = 10.59 Å with a length of L = 50 Å was used in all calculations. Finally, polyethylene matrices with different thicknesses were generated with Materials Studio. A hole of some diameter, approximately 6 Å larger than that of the nanotube, is drilled out of the center of the matrix sample, and a nanotube is inserted into it. The system was then relaxed to equilibrium under zero applied load. The SWCNT/matrix interface is controlled via van der Waals forces and no chemical bonding exists across the interface in this study. Figure 1a is the cross sectional model of the SWCNT/PE nanocomposite, along with the top view of the isolated SWCNT.