While high shear alignment has been shown to improve the mechanical properties of single-wall carbon nanotube (SWNT)-polymer composites, this method does not allow for control over the electrical and dielectric properties of the composite and often results in degradation of these properties. Here, we report a novel method to actively align SWNTs in a polymer matrix, which permits control over the degree of alignment of the SWNTs without the side effects of shear alignment. In this process, SWNTs were aligned via AC field-induced dipolar interactions among the nanotubes in a liquid matrix followed by immobilization by photopolymerization under continued application of the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy, and the morphology of the aligned nanocomposites was investigated by high-resolution scanning electron microscopy. The structure of the field induced aligned SWNTs was intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field parameters.
This work focuses on the derivation of the orientation distribution function (ODF) for a uniaxial-axially symmetric system using polarized Raman spectroscopy. A numerical methodology is proposed to determine the ODF that is formulated in terms of Legendre polynomials and the principle of maximum information entropy. The ultimate goal is to quantify the alignment of single wall nanotubes (SWNTs) in a polymer matrix using the experimental information from the Raman intensity. Some of the mathematical and numerical steps in the determination of ODF, not clarified in the current literature, are shown in this work. The proposed numerical methodology to obtain the ODF is illustrated using an experimental case. Electric field–aligned SWNT-urethane dimethacrylate/1,6-hexanediol dimethacrylate nanocomposites are investigated at different processing conditions to bring forward factors that may enhance the alignment of SWNT inclusions in the polymer. ODF results indicate that the higher electric field frequencies produce a good alignment of the SWNT inclusions; a result also corroborated by optical microscopy imaging and electrical conductivity measurements.
The performance of nanocomposites is affected by dispersion and patterning of the nanoinclusions in the polymer matrix. In this work, electrical and mechanical properties of single wall carbon nanotube polymer composites are tailored using AC electric fields. While the electric field is applied, the polymer is cured to freeze-in the alignment. The specific objectives are: to achieve efficient dispersion of the nanoinclusions in the polymer solutions; to investigate the alignment in liquid polymers in terms of electric field magnitude and frequency; and to quantify the alignment using electrical characterization in the liquid state and mechanical characterization in the solid state.
The nanoscale structure of single-walled carbon nanotubes (SWCNTs) has unique properties. These nanostructured additives can induce unusual characteristic in many polymer matrix. In one of our recent experiments, it was found that when adding SWCNTs into a polyimide (PI) matrix, friction becomes a function of the concentration of the additive. In this research, we analyze the behavior of the SWCNTs-PI nano-composite using an approximation approach. We report that the frictional behavior of the nanocomposite is dominated by the elastic and plastic deformation through randomly dispersed SWCNTs under different loading conditions. At low concentration of SWCNTs, its elasticity dominates the properties of composite while at higher concentration, plastic behavior of tubes plays a major role in describing the properties of composite.
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