Contact Angle Hysteresis on Superhydrophobic Surfaces: An Ionic Liquid Probe Fluid Offers Mechanistic Insight

Krumpfer, J. W. and Bian, P. and Zheng, P. W. and Gao, L. C. and McCarthy, T. J.. (2011) Contact Angle Hysteresis on Superhydrophobic Surfaces: An Ionic Liquid Probe Fluid Offers Mechanistic Insight. Langmuir, 27 (6). pp. 2166-2169. ISSN 0743-7463

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Silicon/silicon dioxide surfaces containing 3 mu m (width) x 6 mu m (length) x 40 mu m (height) staggered rhombus posts were prepared using photolithography and hydrophobized using a, perfluoroallkyl-containing monofunctional silane. These surfaces exhibit water contact angles of theta(A)/theta(R) = 169 degrees/156 degrees. Water drops come to rest on a carefully aligned horizontal sample but roll when the surface is tilted slightly. No visible trail or evidence of water "left behind" at the receding edge of the drop is apparent on surfaces that water drops have rolled on or on samples removed from water through the air-water interface. When dimethylbis(beta-hydroxyethyl)ammonium methanesulfonate (N(+)S(-), a nonvolatile ionic liquid) is used as the liquid probe fluid (instead of water), contact angles of theta(A)/theta(R) = 164 degrees/152 degrees are Observed and similar to 3-mu m-diameter sessile drops are visible (by scanning electron microscopy - SEM) on the top of every post of a sample drawn out of this liquid. We interpret the formation of these sessile microdrops as arising from microcapillary bridge failure that occurs during receding events and emphasize that the capillary bridges rupture in primarily a tensile failure mode. Smaller sessile drops could be prepared using mixtures of Water and N(+)S(-). Microdroplets of N(+)S(-) were also observed to form selectively at particular features on surfaces containing square holes separated by ridges. This suggests that pinning sites can be identified using microscopy and this ionic liquid probe fluid.

Item Type: Article
InterNano Taxonomy: Nanomanufacturing Processes > Nanopatterning/Lithography
Collections: Nanomanufacturing Research Collection > Nanomanufacturing Nanoscale Science and Engineering Centers > Center for Hierarchical Manufacturing
Depositing User: Robert Stevens
Date Deposited: 03 May 2012 18:03
Last Modified: 03 May 2012 18:04

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