Electrothermal flow in dielectrophoresis of single-walled carbon nanotubes

We theoretically investigate the impact of the electrothermal flow on the dielectrophoretic separation of single-walled carbon nanotubes (SWNTs). The electrothermal flow is observed to control the motions of semiconducting SWNTs in a sizable domain near the electrodes under typical experimental conditions, therefore helping the dielectrophoretic force to attract semiconducting SWNTs in a broader range. Moreover, with the increase of the surfactant concentration, the electrothermal flow effect is enhanced, and with the change of frequency, the pattern of the electrothermal flow changes. It is shown that under some typical experimental conditions of dielectrophoretic separation of SWNTs, the electrothermal flow is a dominating factor in determining the motion of SWNTs.

Figure 1

(Color online) Geometry and temperature profiles. (a) Geometry of electrodes used in calculations. (b) Temperature changes with $z$ at $(x,y)=(0\mu \mathrm{m},5\mu \mathrm{m})$, $\varphi$ is $20\mathrm{V}$, and $\omega =300\mathrm{kHz}$.

Figure 2

Forces change with $\varphi$ at $(x,y,z)=(0\mu \mathrm{m},14\mu \mathrm{m},1\mu \mathrm{m})$. The Brownian force profiles overlap on each other.

Figure 3

Forces change with $z$ at $(x,y)=(0\mu \mathrm{m},14\mu \mathrm{m})$ and $\varphi =20\mathrm{V}$. The Brownian force profiles overlap on each other.

Figure 4

Streamlines and corresponding traces of s-SWNTs in 0.1% SDBS solutions; low $\left(300\mathrm{kHz}\right)$ and high $\left(1\mathrm{GHz}\right)$ frequency regimes with $\varphi =20\mathrm{V}$. (a) Streamlines of the electrothermal flow, $\omega =300\mathrm{kHz}$; (b) streamlines of the electrothermal flow, $\omega =1\mathrm{GHz}$; (c) traces of s-SWNTs, $\omega =300\mathrm{kHz}$; and (d) traces of s-SWNTs, $\omega =1\mathrm{GHz}$.