How to make the Cassie wetting state stable?

Gene Whyman; Edward Bormashenko

doi:10.1021/la2011869

How to make the Cassie wetting state stable?

Langmuir. 2011 Jul 5;27(13):8171-6. doi: 10.1021/la2011869. Epub 2011 Jun 6.

Authors

Gene Whyman¹, Edward Bormashenko

Affiliation

¹ Applied Physics Department and Department of Chemistry and Biotechnology Engineering, The Research Institute, Ariel University Center of Samaria, Post Office Box 3, Ariel 40700, Israel.

PMID: 21644550
DOI: 10.1021/la2011869

Abstract

Wetting of rough hydrophilic and hydrophobic surfaces is discussed. The stability of the Cassie state, with air trapped in relief details under the droplet, is necessary for the design of true superhydrophobic surfaces. The potential barrier separating the Cassie state and the Wenzel state, for which the substrate is completely wetted, is calculated for both hydrophobic and hydrophilic surfaces. When the surface is hydrophobic, the multiscaled roughness of pillars constituting the surface increases the potential barrier separating the Cassie and Wenzel states. When water fills the hydrophilic pore, the energy gain due to the wetting of the pore hydrophilic wall is overcompensated by the energy increase because of the growth of the high-energetic liquid-air interface. The potential barrier separating the Cassie and Wenzel states is calculated for various topographies of surfaces. Structural features of reliefs favoring enhanced hydrophobicity are elucidated.