Nenad Miljkovic
Daniel Preston
Massachusetts Institute of Technology

Ryan Enright
Bell Labs Ireland

Alexander Limia
Evelyn Wang
Massachusetts Institute of Technology

Image by N.Miljkovic/D.Preston/MIT

When droplets on a superhydrophobic surface (shown at the top of NMiljkovic1) coalesce during water vapor condensation, the excess surface energy causes the merged droplet to leap off the surface. We observe that upon leaving the surface, the jumping droplets’ trajectory (pictured using long exposure photography) can be bent by an electric field, demonstrating that this ejection process causes them to become charged. The surface shown is nanostructured copper oxide coated with a thin hydrophobic monolayer of tri-chloro silane, rendering it superhydrophobic.

Image by N.Miljkovic/D.Preston/MIT

Here we show a long-exposure-time image of droplets merging during water vapor condensation on a cooled superhydrophobic nanostructured copper oxide tube (outer diameter is 6.35mm, cooling water flow on the inside). Droplets that leap off also repel each other, because they gain a small positive charge during the merging and leaping process. This suggest the electrostatic effect could be exploited to produce surfaces that can be easily cleaned, enhance heat transfer, and anti-icing by the application of an electric field, to aid the droplet removal process.

We gratefully acknowledge funding support from the MIT S3TEC Center, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Basic Energy Sciences under Award no. DE-FG02-09ER46577.

Abstract Link

 http://meetings.aps.org/Meeting/DFD13/Event/204483
 http://meetings.aps.org/Meeting/DFD13/Event/204359

Usage Information

Reporters may freely use this image. Credit N.Miljkovic/D.Preston/MIT

References

N. Miljkovic, D.J. Preston, R. Enright, E.N. Wang, "Electrostatic charging of jumping droplets," Nature Communications, Vol. 4, 2517, 2013. URL: http://www.nature.com/ncomms/2013/130927/ncomms3517/full/ncomms3517.html

N. Miljkovic, R. Enright, Y. Nam, K. Lopez, N. Dou, J. Sack, E.N. Wang, "Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces," Nano Letters, Vol. 13, pp. 179-187, 2013. URL: http://pubs.acs.org/doi/abs/10.1021/nl303835d

Contact Information

Nenad Miljkovic
Postdoctoral Associate, NanoEngineering Group
Department of Mechanical Engineering
Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA, 02139
Tel: 617 981 9247
http://mit.edu/nmiljkov/www/
nmiljkov@mit.edu