Volume 143, 2009
From the journal:

Faraday Discussions

Silica nano-particle super-hydrophobic surfaces: the effects of surface morphology and trapped air pockets on hydrodynamic drainage forces

Derek Y. C. Chan,*a   Md. Hemayet Uddin,bc   Kwun L. Cho,b   Irving I. Liaw,b   Robert N. Lamb,b   Geoffrey W. Stevens,c   Franz Grieserb  and  Raymond R. Dagastine*c  

* Corresponding authors

a Department of Mathematics and Statistics, The Particulate Fluid Processing Centre, The University of Melbourne, Parkville, Victoria, Australia
E-mail: D.Chan@unimelb.edu.au

b School of Chemistry, The Particulate Fluid Processing Centre, The University of Melbourne, Parkville, Victoria, Australia

c Department of Chemical and Biomolecular Engineering, The Particulate Fluid Processing Centre, The University of Melbourne, Parkville, Victoria, Australia
E-mail: rrd@unimelb.edu.au

Abstract

We used atomic force microscopy to study dynamic forces between a rigid silica sphere (radius ∼45 μm) and a silica nano-particle super-hydrophobic surface (SNP-SHS) in aqueous electrolyte, in the presence and absence of surfactant. Characterization of the SNP-SHS surface in air showed a surface roughness of up to two microns. When in contact with an aqueous phase, the SNP-SHS traps large, soft and stable air pockets in the surface interstices. The inherent roughness of the SNP-SHS together with the trapped air pockets are responsible for the superior hydrophobic properties of SNP-SHS such as high equilibrium contact angle (>140°) of water sessile drops on these surfaces and low hydrodynamic friction as observed in force measurements. We also observed that added surfactants adsorbed at the surface of air pockets magnified hydrodynamic interactions involving the SNP-SHS. The dynamic forces between the same silica sphere and a laterally smooth mica surface showed that the fitted Navier slip lengths using the Reynolds lubrication model were an order of magnitude larger than the length scale of the sphere surface roughness. The surface roughness and the lateral heterogeneity of the SNP-SHS hindered attempts to characterize the dynamic response using the Reynolds lubrication model even when augmented with a Navier slip boundary.

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Article information

DOI
https://doi.org/10.1039/B901134J
Article type
Paper
Submitted
19 Jan 2009
Accepted
26 Mar 2009
First published
23 Jul 2009

Faraday Discuss., 2009,143, 151-168

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Silica nano-particle super-hydrophobic surfaces: the effects of surface morphology and trapped air pockets on hydrodynamic drainage forces

D. Y. C. Chan, Md. Hemayet Uddin, K. L. Cho, I. I. Liaw, R. N. Lamb, G. W. Stevens, F. Grieser and R. R. Dagastine, Faraday Discuss., 2009, 143, 151 DOI: 10.1039/B901134J

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