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TECHNICAL PAPERS

Nonequilibrium Molecular Dynamics Approach for Nanoelectromechanical Systems: Nanofluidics and Its Applications

[+] Author and Article Information
Changsung Sean Kim

Corporate R&D Institute, Samsung Electro-Mechanics Co. Ltd., Suwon, 443-743 Koreacsean.kim@samsung.com

J. Fluids Eng 129(9), 1140-1146 (Mar 26, 2007) (7 pages) doi:10.1115/1.2754311 History: Received April 01, 2006; Revised March 26, 2007

Molecular dynamics (MD) simulations have been performed to provide the basic knowledge of nanofluidics and its applications at the molecular level. A nonequilibrium molecular dynamics (NEMD) code was developed and verified by comparing a micro Poiseuille flow with the classical Navier–Stokes solution with nonslip wall boundary conditions. Liquid argon fluids in a platinum nanotube were simulated to characterize the homogeneous fluid system. Also, positively charged particles were mixed with solvent particles to study the non-Newtonian behavior of the heterogeneous fluid. At equilibration state, the macroscopic parameters were calculated using the statistical calculation. As an application of MD simulation, the nanojetting mechanism was identified by simulating the full process of droplet ejection, breakup, wetting on the surface, and natural drying. For an electrowetting phenomenon, a fluid droplet with positive charges moving on the ultrathin film with negative charges was simulated and then compared to the macroscopic experiments. A conceptual nanopumping system using the electrowetting phenomenon was also simulated to prove its feasibility. The molecular dynamics code developed here showed its potential applicability to the novel concept design of nano- and microelectromechanical systems.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cutoff distance (rc) and neighbor lists (rNL) with periodic boundary conditions

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Figure 2

Computing time versus number of particles

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Figure 3

Modeling of a Poiseuille flow in a nanochannel

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Figure 4

Velocity profiles in the z direction of two pressure-driven flows

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Figure 5

Liquid argon flowing through a platinum nanotube of 12nmdia

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Figure 6

Axial velocity profiles due to cutoff distance

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Figure 7

Axial velocity profiles due to nanotube diameter

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Figure 8

Electrostatic flows in a nanotube of 9nmdia: (a)qw=+0.833e and (b)qw=−0.833e

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Figure 9

Axial velocity profiles due to surface charges at wall

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Figure 10

Evolution of nanojetting from droplet ejection to surface wetting: (a)t=0.084ns, (b)t=0.116ns, (c)t=0.148ns, (d)t=0.180ns, (e)t=0.212ns, (f)t=0.244ns, (g)t=0.276ns, (h)t=0.324ns, and (i)t=0.368ns

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Figure 11

Contact angle (CA) and surface wettability at equilibration state (Both photographs with permission of Prof. K. Tsujii at Hokkaido University (15)): (a)CA=0deg (fully wetting, α=1, β=1), (b)CA≅109deg (α=1, β=0.25), and (c)CA≅174deg (Hydrophobic, α=1, β=0.1)

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Figure 12

Concept design for nanopumping system (a) Schematics of an electrowetting pump and (b) Simplified modeling of a nanopump

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Figure 13

Nano-pump using electrowetting phenomenon: (a)t=0.6ns (electrode 2), (b)t=1.6ns (electrode 3), (c)t=2.6ns (electrode 4), and (d)t=3.6ns (electrode 1)

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Figure 14

Instantaneous velocity vectors of the droplet in motion: (a)t=0.6ns and (b)t=1.6ns

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Figure 15

Averaged magnitude of axial velocity of the droplet

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