^{1,a)}, Hong-Fei Ye

^{2}, Zhen Liu

^{3}, Jian-Ning Ding

^{1}, Guang-Gui Cheng

^{1}, Zhi-Yong Ling

^{1}, Yong-Gang Zheng

^{2}, Lei Wang

^{4}and Jin-Bao Wang

^{2,5}

### Abstract

In this paper, a carbon nanotube-based charge-controlled speed-regulating nanoclutch (CNT-CC-SRNC), composed of an inner carbon nanotube(CNT), an outer CNT, and the water confined between the two CNT walls, is proposed by utilizing electrowetting-induced improvement of the friction at the interfaces between water and CNT walls. As the inner CNT is the driving axle, molecular dynamics simulation results demonstrate that CNT-CC-SRNC is in the disengaged state for the uncharged CNTs, whereas water confined in the two chargedCNT walls can transmit the torque from the inner tube to the outer tube. Importantly, the proposed CNT-CC-SRNC can perform stepless speed-regulating function through changing the magnitude of the charge assigned on CNT atoms.

This work was supported by the National Natural Science Foundation of China (11102074, 51005103, 11102058, 10902021), the Natural Science Foundation of Jiangsu Province (BK2011463), China Postdoctoral Science Foundation (2011M501169, 20100470072), Postdoctoral Science Foundation of Jiangsu Province (1102112C), and Initial Funding of Jiangsu University (11JDG024).

I. INTRODUCTION

II. MODEL AND METHODS

III. RESULTS AND DISCUSSION

IV. CONCLUSION

### Key Topics

- Carbon nanotubes
- 47.0
- Friction
- 13.0
- Carbon
- 7.0
- Water transportation
- 7.0
- Molecular dynamics
- 6.0

##### B82B1/00

## Figures

(a) Cross sectional view of the proposed CNT-CC-SRNC model. Two pink circles are inner and outer CNTs with radii *R _{i} * and

*R*, respectively. In this work,

_{o}*R*for (20, 20) CNT is 1.3846 nm and

_{i}*R*for (40, 40) CNT is 2.7693 nm. Green and white particles represent oxygen and hydrogen atoms of water molecules, respectively. While the inner CNT rotates at an angular velocity of rad/ns, we assume the angular velocity of outer CNT is rad/ns. (b) Geometry of the charged CNT surface. Blue and black spheres represent the carbon atoms of positive and negative charges, respectively.

_{o}(a) Cross sectional view of the proposed CNT-CC-SRNC model. Two pink circles are inner and outer CNTs with radii *R _{i} * and

*R*, respectively. In this work,

_{o}*R*for (20, 20) CNT is 1.3846 nm and

_{i}*R*for (40, 40) CNT is 2.7693 nm. Green and white particles represent oxygen and hydrogen atoms of water molecules, respectively. While the inner CNT rotates at an angular velocity of rad/ns, we assume the angular velocity of outer CNT is rad/ns. (b) Geometry of the charged CNT surface. Blue and black spheres represent the carbon atoms of positive and negative charges, respectively.

_{o}The angular velocity of the outer CNT versus the charge magnitude *q* on carbon atoms for the inner CNT rotating at a constant angular velocity of 100 rad/ns.

The angular velocity of the outer CNT versus the charge magnitude *q* on carbon atoms for the inner CNT rotating at a constant angular velocity of 100 rad/ns.

For *q* = 1.0 *e*, the angular velocity of the outer CNT versus the rotational period of the inner CNT. The solid line represents the linear fit of the MD data.

For *q* = 1.0 *e*, the angular velocity of the outer CNT versus the rotational period of the inner CNT. The solid line represents the linear fit of the MD data.

For the rotational period of the inner CNT = 20 ps, the angular velocity profiles of confined water in CNT-CC-SRNC model along theradial direction of CNTs for the charge magnitude on carbon atoms *q* in the range of 0.0 *e* (uncharged) to 1.0 *e*. The partial enlarged drawing presents thedetails of the profiles with the radial distance in the range of 2.05–2.45 nm to illustrate the motion of boundary water molecules adjacent to the outer CNT.

For the rotational period of the inner CNT = 20 ps, the angular velocity profiles of confined water in CNT-CC-SRNC model along theradial direction of CNTs for the charge magnitude on carbon atoms *q* in the range of 0.0 *e* (uncharged) to 1.0 *e*. The partial enlarged drawing presents thedetails of the profiles with the radial distance in the range of 2.05–2.45 nm to illustrate the motion of boundary water molecules adjacent to the outer CNT.

For the rotational period of the inner CNT = 20 ps, the angular velocity profiles of confined water in CNT-CC-SRNC model along the radial direction of CNTs for water temperature of 200, 300, and 400 K, respectively. The partial enlarged drawing presents the details of the profiles with the radial distance in the range of 2.05–2.45 nm to illustrate the motion of boundary water molecules adjacent to the outer CNT.

For the rotational period of the inner CNT = 20 ps, the angular velocity profiles of confined water in CNT-CC-SRNC model along the radial direction of CNTs for water temperature of 200, 300, and 400 K, respectively. The partial enlarged drawing presents the details of the profiles with the radial distance in the range of 2.05–2.45 nm to illustrate the motion of boundary water molecules adjacent to the outer CNT.

For the rotational period of the inner CNT = 20 ps, the number density of water molecules in CNT-CC-SRNC model along the radial direction of CNTs for water temperature of 200, 300, and 400 K, respectively.

For the rotational period of the inner CNT = 20 ps, the number density of water molecules in CNT-CC-SRNC model along the radial direction of CNTs for water temperature of 200, 300, and 400 K, respectively.

The angular velocity profiles of confined water in CNT-CC-SRNC model along the radial direction of CNTs for the inner CNT-driven and outer CNT-driven modes. The CNT rotating angular velocity is 100 rad/ns.

The angular velocity profiles of confined water in CNT-CC-SRNC model along the radial direction of CNTs for the inner CNT-driven and outer CNT-driven modes. The CNT rotating angular velocity is 100 rad/ns.

## Tables

Boundary slip velocity *v _{s} *, interfacial shear stress , and the interfacial friction coefficient

*f*= at the interface between inner CNT and water for the inner CNT rotating at a constant angular velocity of 100 rad/ns.

*q*varies in the range of 0.0–1.0 e.

Boundary slip velocity *v _{s} *, interfacial shear stress , and the interfacial friction coefficient

*f*= at the interface between inner CNT and water for the inner CNT rotating at a constant angular velocity of 100 rad/ns.

*q*varies in the range of 0.0–1.0 e.

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