Controlling the Carbon Nanotube-to-Medium Conductivity Ratio for Dielectrophoretic Separation

Abstract

The surface conductivity of colloidal nanotubes, induced by ionic surfactants, is known to affect alternating current dielectrophoresis, which has been actively investigated with regard to separating single-walled carbon nanotubes according to electronic type. The nanotube-to-suspending medium conductivity ratio is a primary factor for determining the dielectrophoretic behavior of semiconducting nanotubes. In this study, our theoretical and experimental analysis revealed that the suspending medium conductivity also plays an important role in controlling the conductivity ratio. This work elucidates the effects of several surfactant systems on the conductivity ratio and therefore the degree of separation between metallic and semiconducting nanotubes. The equimolar mixture of anionic and cationic surfactants was more effective than a nonionic polymer in reducing the conductivity ratio because the conductivity of colloidal nanotubes was decreased and that of the suspending medium was increased. Besides, the surfactant mixture provided a better dispersion of nanotubes. The dielectrophoretic separation was carried out using microelectrodes with a gap size of 4 mum at an electric field frequency of 10 MHz. The complete separation of nanotubes at the reduced conductivity ratio was confirmed by Raman spectroscopy and electrical transport measurements.

Single-Walled Carbon Nanotubes Probed with Insulator-Based Dielectrophoresis

“…This conclusion is in agreement with reports by Kang et al, who observed a relation between the dielectrophoretic behavior of surfactant-suspended SWNTs with the type of surfactant and concomitant changes in the ζ potential. 50 Similar observations were also recently made with biological cells. Tang et al reported that the dielectrophoretic behavior of yeast cells changes through the surface interaction with surfactants such as sodium dodecyl sulfate.…”

“…In the case of a hollow tube, the geometry factor will be replaced by πlδ (2 r – δ) with the wall thickness δ. E is the electric field and Re (CM) is the real part of the Clausius–Mossotti factor. The DEP force acting on a SWNT depends on the radius and length as well as the magnitude and sign of the Clausius–Mossotti factor (CM), which describes the electrical polarizability of the material: 30 , 31 , 50 with where ε p is the permittivity of the particle; σ m and σ p are the conductivity of the medium and particle, respectively; ω is the frequency; and L denotes the dimensionless depolarization factor parallel to the electric field and along the long axis of the nanotube, which is defined as 46 …”

Stretchable current collectors based on carbon embedded in a poly (acrylamide)/poly (N,N-methylenebisacrylamide) hydrogel modified with Nafion 117®

“…Also, it has been postulated that homogeneity of carbon suspension depends on charge distribution at the carbon/solvent interface [27] and the interaction between polarized layers is defined by hydrodynamic shear factor known as zeta (ξ)-potential [28]. This potential depends on the chemical properties of both particle surface and solution composition (i.e., pH).…”

Carbon nanotube dielectrophoresis: Theory and applications

“…Similarly, Kang et al. [142] and Krupke et al. [60] reported that the surface charge of SWNTs plays an important role in controlling the conductivity ratio, which can switch the SWNT DEP behavior.…”