Nanochannels DOI: 10.1002/ange.201408633 Electromanipulating Water Flow in Nanochannels** Jianlong Kou, Jun Yao,* Hangjun Lu, Bo Zhang, Aifen Li, Zhixue Sun, Jianguang Zhang, Yunzhang Fang, Fengmin Wu, and Jintu Fan Abstract: In sharp contrast to the prevailing view that a sta- tionary charge outside a nanochannel impedes water perme- ation across the nanochannel, molecular dynamics simulations show that a vibrational charge outside the nanochannel can promote water flux. In the vibrational charge system, a decrease in the distance between the charge and the nanochannel leads to an increase in the water net flux, which is contrary to that of the fixed-charge system. The increase in net water flux is the result of the vibrational charge-induced disruption of hydrogen bonds when the net water flux is strongly affected by the vibrational frequency of the charge. In particular, the net flux is reaches a maximum when the vibrational frequency matches the inherent frequency of hydrogen bond inside the nano- channel. This electromanipulating transport phenomenon provides an important new mechanism of water transport confined in nanochannels. Understanding the water transport through nanochannels is essential to uncovering the complex mechanisms of water permeation through biological membranes and porous media and developing advanced nanofluidic systems for various applications. In recent years, water transport through nano- channels and water structures inside the nanochannels were extensively investigated, and some unconventional phenom- ena were revealed. For example, both molecular dynamics (MD) simulations [1, 2] and experiments [3] demonstrated that the flow rate through a carbon nanotube is three to five orders of magnitude faster than that predicted from conventional fluid-flow theory, which compares favorably with those inside the biological channels, proving the necessity to understand water transport in a confined nanochannel. It was reported that charged residues exist in biological protein channels and play a vital role in water permeation. [4–6] Since water molecules in the carbon nanotube share many characteristics with those inside the biological channels, [1, 7] for example, the single-file arrangement, the wavelike density distribution and the wet–dry transition, a number of research- ers used nanotubes as a model to study the complex water transport in biological channels. [8] It has been widely reported that water permeation through a nanochannel can be shut down by placing a stationary charge close to the channel wall, so-called electro-gating. [9, 10] These studies formed a prevailing view that charges next to nanochannels can greatly reduce and even block the water permeation through the nano- channel. Biological channels are actually exposed to vibra- tional electrical signals due to metabolism. [5, 11] However, how a vibrational charge next to a nanochannel affect the trans- port of water molecules has not been properly understood. Herein, we report a surprising finding from molecular dynamics simulations, namely that water flow through a con- fined nanochannel can be sped up by placing a vibrational charge next to the nanochannel. This unexpected vibration- charge-induced fast flow of water molecules, which can be named electro-propelling, is a result of the disruption of the hydrogen bond of water molecules confined inside the nanochannel. We show that by manipulating the vibrational frequency of the charge as well as the distance between the charge and the nanochannel, the net flux of water in the nanochannel can be regulated over a wide range. We there- fore name this phenomenon electromanipulating. The simulation setup consists of an unperturbed single- wall carbon nanotube (SWCNT) and two graphenes, which are dissolved in a water bath, as shown in Figure 1a. A (6,6) SWCNT of 0.81 nm in diameter and 13.4 nm in length is embedded between two monolayer graphenes with a pore diameter slightly larger than the diameter of SWCNT along the z direction, that is, being vertical to the surface of the graphenes. The choice of the SWCNT is based on the fact that a nanochannel of (6,6) SWCNT can share the properties of biological channels. [1, 7] The graphenes are impermeable to water. The space between the two graphenes is vacuum. Water can only be transported between the two graphenes through the SWCNT. To study the behavior of the water permeation through a nanochannel with a vibrational charge, a periodically vibrational positive charge of 1.0 e with a distance d from the nearest carbon atoms of the SWCNT is imposed at the center outside the SWCNT. The charge vibrates periodically along the direction parallel to the SWCNT surface and satisfies the relation z(t) = A cos(2 pft + f), where A is the amplitude, f is the vibrational [*] J. Kou, Prof. J. Yao, B. Zhang, Prof. A. Li, Dr. Z. Sun, Dr. J. Zhang State Key Laboratory of Heavy Oil Processing China University of Petroleum (East China) Qingdao 266580 (China) E-mail: yaojunhdpu@126.com J. Kou, Dr. H. Lu, Prof. Y. Fang, Prof. F. Wu Institute of Condensed Matter Physics Zhejiang Normal University, Jinhua 321004 (China) Prof. J. Fan Department of Fiber Science and Apparel Design Cornell University, Ithaca, New York 14853-4401 (USA) [**] We thank Prof. Ruhong Zhou for critical comments on the manuscript. This work was supported by the NSFC (11405146, 61274099, 51234007, 51404291, and 51490654), NBRPC (2012CB825700), PCSIRT (IRT1294), Shandong Provincial NSFC (ZR2013DL011), Zhejiang Provincial Science and Technology Key Innovation Team (2011R50012-2) and Key Laboratory (2013E10022). J.Y. acknowledge the Climb Taishan Scholar Program in Shandong Province. J.T.F. was supported by the Start-up fund of Cornell University. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201408633. A ngewandte Chemi e 2381 Angew. Chem. 2015, 127, 2381 –2385  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim