Aligned single‐wall carbon nanotube polymer composites using an electric field

Abstract

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.

A review and analysis of electrical percolation in carbon nanotube polymer composites

“…When approaching statistical percolation the mobility of CNT is reduced and the effect of the electric field vanishes. The formation of AC electric field induced aligned SWCNT percolative columns between electrodes has also been observed by Park et al in SWCNT/UDMA/HDDMA composites [38]. …”

Analyzing the quality of carbon nanotube dispersions in polymers using scanning electron microscopy

“…We were able to take similar images with the ET detector of a JSM-840A SEM from Jeol. The InLens detector from Hitachi SEM devices is also sensitive to voltage contrast [64,65,69,70], but as it works different than ours, it seems to be immune to excessive surface charging at the same time. Thus, as long as the electric field influence for new detector (InLens) or microscope types (ESEM, LVSEM) are not explored, attention has to be paid to the choice of the detector [75].…”

“…Lillehei et al contributed a NIST practice guide in 2005 on how to characterize the dispersion of carbon nanotubes in a polymer matrix [62]. Voltage contrast images of nanotubes were already published before 2005 [63][64][65][66][67] and also thereafter [68][69][70], unfortunately without exploring and explaining how to make such images.…”

Pearl-Chain Formation of Discontinuous Carbon Fiber under an Electrical Field

“…Thus, alignment of short carbon fiber is of great importance, e.g., carbon nanotubes (CNTs) have the same anisotropic properties and have been widely investigated in composite study [8,9]. There have been different processes documented in literature in order to align short fibers (or CNTs), e.g., magnetic field [10][11][12][13], gas flow [14,15], shear flow [2,[16][17][18], mechanical shear press [2,19,20], mechanical stretch [21], and electrical field [22][23][24][25][26][27][28]. While mechanical methods of alignment allow production of large size samples, it is still costly and has specific requirements for sample preparation [22].…”