Design of surface hierarchy for extreme hydrophobicity

Yongjoo Kwon, Neelesh Patankar, Junkyu Choi, Junghoon Lee*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

212 Scopus citations


An extreme water-repellent surface is designed and fabricated with a hierarchical integration of nano- and microscale textures. We combined the two readily accessible etching techniques, a standard deep silicon etching, and a gas phase isotropic etching (XeF 2) for the uniform formation of double roughness on a silicon surface. The fabricated synthetic surface shows the hallmarks of the Lotus effect: durable super water repellency (contact angle < 173°) and the sole existence of the Cassie state even with a very large spacing between roughness structures (<1:7.5). We directly demonstrate the absence of the Wenzel's or wetted state through a series of experiments. When a water droplet is squeezed or dropped on the fabricated surface, the contact angle hardly changes and the released droplet instantly springs back without remaining wetted on the surface. We also show that a ball of water droplet keeps bouncing on the surface. Furthermore, the droplet shows very small contact angle hysteresis which can be further used in applications such as super-repellent coating and low-drag microfludics. These properties are attributed to the nano/micro surface texture designed to keep the nonwetting state energetically favorable.

Original languageEnglish (US)
Pages (from-to)6129-6136
Number of pages8
Issue number11
StatePublished - Jun 2 2009

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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