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Research Papers

The Effect of Water Droplet Size, Temperature, and Impingement Velocity on Gold Wettability at the Nanoscale

[+] Author and Article Information
Jhonatam Cordeiro

Department of Industrial and Systems
Engineering,
North Carolina A&T State University,
419 McNair Hall,
1601, East Market Street,
Greensboro, NC 27411
e-mail: jcrodrig@aggies.ncat.edu

Salil Desai

Department of Industrial and Systems
Engineering,
North Carolina A&T State University,
423 McNair Hall,
1601, East Market Street,
Greensboro, NC 27411
e-mail: sdesai@ncat.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received January 20, 2017; final manuscript received May 17, 2017; published online June 13, 2017. Assoc. Editor: Ulf Engel.

J. Micro Nano-Manuf 5(3), 031008 (Jun 13, 2017) (8 pages) Paper No: JMNM-17-1004; doi: 10.1115/1.4036891 History: Received January 20, 2017; Revised May 17, 2017

Molecular dynamics (MD) simulations are performed to investigate the wettability of gold substrate interacting with nanosized droplets of water. The effects of droplet size, temperature variation, and impingement velocity are evaluated using molecular trajectories, dynamic contact angle, spread ratios, radial distribution function (RDF), and molecular diffusion graphs. Droplets of 4 nm and 10 nm were simulated at 293 K and 373 K, respectively. Stationary droplets were compared to droplets impinging the substrate at 100 m/s. The simulations were executed on high-end workstations equipped with NVIDIA® Tesla graphical processing units (GPUs). Results show that smaller droplets have a faster stabilization time and lower contact angles than larger droplets. With an increase in temperature, stabilization time gets faster, and the molecular diffusion from the water droplet increases. Higher temperatures also increase the wettability of the gold substrate, wherein droplets present a lower contact angle and a higher spread ratio. Droplets that impact the substrate at a higher impingement velocity converge to the same contact angle as stationary droplets. At higher temperatures, the impingement velocities accelerate the diffusion of water molecules into vapor. It was revealed that impingement velocities do not influence stabilization times. This research establishes relationships among different process parameters to control the wettability of water on gold substrates which can be explored to study several nanomanufacturing processes.

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References

Figures

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Fig. 1

Four nanometer and 10 nm droplets models on top of a gold substrate

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Fig. 2

Progression of 4 nm and 10 nm droplets with impingement velocity of 100 m/s

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Fig. 3

(a) Water model with vapor periphery and (b) density separation contour

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Fig. 4

RMSD of nanodroplets at 293 K

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Fig. 5

RMSD of nanodroplets at 373 K

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Fig. 6

Spread ratio of 4 nm and 10 nm droplets

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Fig. 7

Contact angles of 4 nm and 10 nm droplets

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Fig. 8

RDF of the 10 nm droplet at different ambient conditions

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Fig. 9

Contact angles of 10 nm droplets at 293 K and 373 K

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Fig. 10

Spread ratio of a 10 nm droplet at 293 K and 373 K

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Fig. 11

Diffusion of atoms in the (a) 4 nm and (b) 10 nm droplet

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Fig. 12

Diffusion of atoms in the (a) 4 nm and (b) 10 nm droplet at 373 K

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Fig. 13

Dynamic contact angles for (a) 4 nm and (b) 10 nm droplets at 293 K

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Fig. 14

Spread ratios for (a) 4 nm and (b) 10 nm at 293 K

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