Molecular Dynamics Simulation of Composite Nanochannels as Nanopumps Driven by Symmetric Temperature Gradients

Liu, Chong; Li, Zhigang

doi:10.1103/physrevlett.105.174501

Cited by 73 publications

(48 citation statements)

References 22 publications

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“…1,3,24 Recently, we studied nanochannel flows and found that the coupling of temperature and surface effects could lead to different flow fashions. 4,25 We have numerically demonstrated that a fluid can be continuously circulated by a symmetric temperature gradient in nanochannels of heterogeneous surface energies. This fluid transport mechanism can be employed for thermal management by using the waste heat generated by chips/devices instead of external forces.…”

Section: Introductionmentioning

confidence: 99%

Fluid transport in nanochannels induced by temperature gradients

Liu

Ya²,

Li³

2012

The Journal of Chemical Physics

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We investigate the mechanisms of fluid transport driven by temperature gradients in nanochannels through molecular dynamics simulations. It is found that the fluid-wall interaction is critical in determining the flow direction. In channels of very low surface energy, where the fluid-wall binding energy ε fw is small, the fluid moves from high to low temperature and the flow is induced by a potential ratchet near the wall. In high surface energy channels, however, the fluid is pumped from low to high temperature and the pressure drop caused by the temperature gradient is the major driving force. In addition, as the fluid-wall interaction is strengthened, the flow flux assumes a maximum, where ε fw is close to the lower temperature T L of the channel and ε fw /kT L ≈ 1 is roughly satisfied.

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Section: Introductionmentioning

confidence: 99%

Fluid transport in nanochannels induced by temperature gradients

Liu

Ya²,

Li³

2012

The Journal of Chemical Physics

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“…The ability to externally induce the movement and directly study the motion of model nanodroplets in contact with substrate interface may provide an insight to dynamic properties of interfacial water by experimentally complementing theoretical simulations. Such studies will be critical in the design of materials tailored to the adhesion and flow of liquids at the interface (20,21).…”

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confidence: 99%

Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

Mirsaidov

Zheng

Bhattacharya

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

108

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Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface. At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10-to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps. We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state. Although much is known about the movement of bulk water, most of what is known about interfacial water results from modeling and computational simulations (9, 10). Nanometer-diameter water droplets, because of their high surface-to-volume ratio and small number of molecules, present an ideal system for theoretical explorations of interfacial water dynamics induced by external forces. Such studies describe how external driving forces imposed by thermal (11), chemical (12), and topographic gradients (13) can lead to motion of nanometer-diameter droplets, and local fluctuations may result in the breakup of liquid nanojets (14). These theories imply that perturbations, either from external physical forces or chemical nonuniformities are coupled to dynamics of a nanodroplet through changes in shape and thus causing translocation of nanometer size droplets. Interestingly, very recent simulations also predict that nanometer-diameter water droplets will slip on hydrophilic surfaces (15) similar to those on hydrophobic surfaces (16,17). However, studying the structural dynamics of nanodroplets is experimentally challenging because one needs to be able to externally induce the movement and be able to image the subsequent dynamic process of nanoscale droplets. Although atomic force microscope probes have measured the interfacial forces between liquids (18) and scanning transmission electron microscopy (TEM) has imaged small numbers of static water molecules confined in carbon nanotubes (19), these approaches fail to directly relate structure and dynamics of nanoscopic liquids. The ability to externally induce the movement and directly study the motion of model nanodroplets in contact with substrate interface may provide an insight to dynamic properties of interfacial water by experimentally complementing theoretical simulations. Such studies will be critical in the design of materials tailored to the adhesion and flow of liquids at the interface (20, 21).Hydrodynamic slip of water that re...

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“…This means that drug molecules dissolved in a water droplet and can be delivered to a target area along the CNTs. Previous works have shown that the boundary condition is a critical issue in nanoscale systems [29,30]. Hummer et al [31] and Wu et al [32] have shown that a minute change in the attraction between the tube wall and water can dramatically affect pore hydration, leading to a sharp transition between empty and filled states within a nanosecond time scale.…”

Section: Introductionmentioning

confidence: 99%

Unidirectional motion of a water nanodroplet subjected to a surface energy gradient

Kou

Mei

et al. 2012

Phys. Rev. E

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We perform molecular dynamics simulations to demonstrate that when a nanodroplet is confined inside a carbon nanotube (CNT), unidirectional motion can be created by a nonzero surface energy gradient. It is found that the water nanodroplet moves along the direction of increasing surface energy. The transportation efficiency of the water nanodroplet is found to be dependent on the surface energy gradient; environmental temperature; and the flexibility, diameter, and defectiveness of the CNT. It is shown that higher surface energy gradient, the smaller diameter of the CNT, and fewer defects promote higher transportation efficiency. However, when the temperature is too high or too low, the water transport across the CNT is impeded. Except for the initial stage at the relatively low environmental temperature, higher flexibility of the CNT wall reduces the transportation efficiency. It is also found that the hydrogen bonds of water molecules play a role in the dynamic acceleration process with a wavelike feature. The present work provides insight for the development of CNT devices for applications such as drug delivery, nanopumps, chemical process control, and molecular medicine.

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Molecular Dynamics Simulation of Composite Nanochannels as Nanopumps Driven by Symmetric Temperature Gradients

Cited by 73 publications

References 22 publications

Fluid transport in nanochannels induced by temperature gradients

Fluid transport in nanochannels induced by temperature gradients

Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

Unidirectional motion of a water nanodroplet subjected to a surface energy gradient

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