The reversible actuation of droplets on superhydrophobic surfaces under ambient conditions is currently an important field of research due to its potential applicability in microfluidic lab-on-a-chip devices. We have recently shown that Si-nanowire (NW) surfaces allow for reversible actuation provided that the surface structures show certain characteristics. In particular it appears that, for such surfaces, the presence of structures with multiple specific length scales is indeed needed to have a robust reversibility of contact angle changes. Here we report on electrowetting (EW) and impalement experiments on double-scale structured surfaces prepared by a combination of silicon micropillars prepared by an association of optical lithography and silicon etching, and nanowire growth on top of these surfaces. We show that while micropillar surfaces have a low impalement threshold and irreversible EW behaviour, a surface with double-scale texture can show both a very high resistance to impalement and a limited reversibility under EW, provided that the roughness of the micro-scale is large enough - i.e. that the pillars are tall enough. The optimal performance is obtained for a space between pillars that is comparable to the height of the nanostructure.

Item Type:	Refereed Article
Research Division:	Engineering
Research Group:	Fluid mechanics and thermal engineering
Research Field:	Fluid mechanics and thermal engineering not elsewhere classified
Objective Division:	Manufacturing
Objective Group:	Instrumentation
Objective Field:	Scientific instruments
ID Code:	99998
Year Published:	2010
Web of Science® Times Cited:	29
Deposited By:	Austn Centre for Research in Separation Science
Deposited On:	2015-04-22
Last Modified:	2015-05-07
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