Dynamics of carbon nanotube alignment by electric fields

Abstract

The dynamics of multiwall carbon nanotube (MWCNT) alignment inside viscous media using electric fields is investigated. Electrical current measurements were performed in situ during the application of an electric field to liquid solutions of deionized water or dissolved polymer containing MWCNTs. The variation of electrical current over time was associated to the dynamics of the MWCNT network formation. The influence of the electric field magnitude and frequency on the MWCNT network formation was studied. MWCNT migration towards the negative electrode was observed when a direct current electric field was applied, whereas formation of an aligned MWCNT network was achieved for an alternating current electric field. The increase of the electric field frequency promotes a faster formation of an aligned MWCNT network and thinner MWCNT bundles. A higher viscosity of the liquid medium yields slower MWCNT alignment evidenced by a slower change of electrical current through the viscous system. An analytical model based on the dielectrophoresis-induced torque, which considers the viscosity of the medium, is also proposed to explain the dynamics of MWCNT alignment. Furthermore, aligned MWCNT/polysulfone solid composites were fabricated and electrically characterized. The solid composites presented anisotropic electrical conductivity, which was more evident for low MWCNT concentrations (0.1-0.2 wt%).

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

“…Depending on the rolling direction and the diameter, single-walled carbon nanotubes (SWCNTs) are metallic or semiconductive while multi-walled carbon nanotubes (MWCNTs) are always metallic. The electric conductivity is higher along the CNT longitudinal axis than in the transversal direction [20]. Longitudinal electronic transport is ballistic (i.e.…”

Chiral-index resolved length mapping of carbon nanotubes in solution using electric-field induced differential absorption spectroscopy

“…In fact, electric-field induced alignment of SWCNTs in dispersion is not new and has been reported before. [14][15][16] However previous works in aqueous media could only resolve alignment of bundles of SWCNTs and not of well dispersed individual SWCNTs. Using a low-k solvent instead of water, it is in fact possible to resolve the field alignment of individually dispersed SWCNTs as we will show in this work.…”

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

“…An inequality can be formed using (25) and after making a substitution 2×r avg = d, the following inequality can be derived…”

“…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].…”