Measurement of contact-angle hysteresis for droplets on nanopillared surface and in the Cassie and Wenzel states

A molecular dynamics simulation study

Takahiro Koishi, Kenji Yasuoka, Shigenori Fujikawa, Xiao Cheng Zeng

Research output: Contribution to journalArticle

85 Citations (Scopus)

Abstract

We perform large-scale molecular dynamics simulations to measure the contact-angle hysteresis for a nanodroplet of water placed on a nanopillared surface. The water droplet can be in either the Cassie state (droplet being on top of the nanopillared surface) or the Wenzel state (droplet being in contact with the bottom of nanopillar grooves). To measure the contact-angle hysteresis in a quantitative fashion, the molecular dynamics simulation is designed such that the number of water molecules in the droplets can be systematically varied, but the number of base nanopillars that are in direct contact with the droplets is fixed. We find that the contact-angle hysteresis for the droplet in the Cassie state is weaker than that in the Wenzel state. This conclusion is consistent with the experimental observation. We also test a different definition of the contact-angle hysteresis, which can be extended to estimate hysteresis between the Cassie and Wenzel state. The idea is motivated from the appearance of the hysteresis loop typically seen in computer simulation of the first-order phase transition, which stems from the metastability of a system in different thermodynamic states. Since the initial shape of the droplet can be controlled arbitrarily in the computer simulation, the number of base nanopillars that are in contact with the droplet can be controlled as well. We show that the measured contact-angle hysteresis according to the second definition is indeed very sensitive to the initial shape of the droplet. Nevertheless, the contact-angle hystereses measured based on the conventional and new definition seem converging in the large droplet limit.

Original languageEnglish
Pages (from-to)6834-6842
Number of pages9
JournalACS Nano
Volume5
Issue number9
DOIs
Publication statusPublished - 2011 Sep 27

Fingerprint

Contact angle
Hysteresis
Molecular dynamics
hysteresis
molecular dynamics
Computer simulation
simulation
Contacts (fluid mechanics)
computerized simulation
Water
water
stems
metastable state
grooves
Hysteresis loops
thermodynamics
Phase transitions
Thermodynamics
estimates
Molecules

Keywords

  • contact angle
  • hysteresis
  • molecular dynamics simulation
  • nanopillared surface
  • Wenzel and Cassie states

ASJC Scopus subject areas

  • Engineering(all)
  • Materials Science(all)
  • Physics and Astronomy(all)

Cite this

Measurement of contact-angle hysteresis for droplets on nanopillared surface and in the Cassie and Wenzel states : A molecular dynamics simulation study. / Koishi, Takahiro; Yasuoka, Kenji; Fujikawa, Shigenori; Zeng, Xiao Cheng.

In: ACS Nano, Vol. 5, No. 9, 27.09.2011, p. 6834-6842.

Research output: Contribution to journalArticle

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