Nanotech 2010

Adhesion of Water on Flat Polymer Surfaces and Superhydrophobic Surfaces (invited presentation)

K.Y. Law, H. Zhao, B. Samuel
Xerox Corporation, US

Keywords: adhesion, superhydrophobic surfaces


The interaction of water droplet with flat polymer surfaces of varying hydrophobicity (contact angle) has been studied using a high-sensitivity microelectromechanical balance system (tensiometer). Both attractive force and pull-off force are studied as the water droplet is approaching and separating from the surface. While the attractive force of water on these surfaces is found to correlate well to the advancing/static water contact angle, the contrary can be said about the pull off force, which is a measure of adhesion between the water droplet and the surface of interest. Rather the pull off force was shown to correlate reasonably well to the receding angle. In this work, we extend our study to measure the interactions of water droplet with rough/textured surfaces with very high water contract angles, ranging from 130 to 160 degree. The attractive force between the water droplet and these surfaces are found to be negligible, which is consistent to their high contact angles. Very interesting results are obtained with the pull off force measurements. Evidence is provided that the adhesion between water and the rough surface can be as strong as the flat polymer surface when the water droplet is in the Wenzel state at the composite interface. Results on the adhesion of water on superhydrophobic surfaces that are in Cassie-Baxter state will be presented and discussed.
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