With the development of efficient methods to prepare stable suspensions of individualized single-wall carbon nanotubes (SWNT) research has focused on manipulating suspended SWNTs using dielectrophoretic forces [1,2]. One of the goals is to separate the metallic from the semiconducting SWNTs [3,4]; this should be possible because at frequencies in the range 1-100 MHz the dielectrophoretic force on metallic tubes can be up to two orders of magnitude higher than the one on semiconductors. This is due to the difference in the permittivities and conductivities between the metallic and semiconducting SWNTs. We have developed an efficient SWNT separation device where dispersed nanotubes flow between two coaxial cylinders subjected to an AC voltage difference with a DC offset. The DC offset exerts an electrophoretic force on the charged surfactants that stabilize the SWNTs in water. This drags the wrapped SWNTs near the inner cylindrical electrode where the dielectrophoretic force, caused by the AC field, is higher. Because of the simple geometry, the velocity profile and the electric fields can be described analytically. We use Brownian dynamics to simulate dilute suspensions of SWNTs and predict the motion of both metallic and semiconducting tubes under the action of the fluid flow, both electric forces, and the random Brownian force. We compare numerical and experimental results to access the effectiveness of Brownian dynamics in modelling the dielectrophoretic behaviour of SWNTs.

References:

[1] – Rosa H. M. Chan et al. Nanotechnology, vol. 15, S672-S677 (2004)

[2] – Ji-Eun Kim and Chang-Soo Han. Nanotechnology, vol. 16, 2245-2250 (2005)

[3] – Ralph Krupke et al. Science, vol. 301, 344-347 (2003)

[4] – Maria Dimaki and Peter Boggild. Nanotechnology, vol. 15, 1095-1102 (2004)