8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Thu 811:10-14:00P7.117Suspension of water droplets on individual pillarsTamara Tóth, 1 Davide Ferraro, 1 Matteo Pierno, 1 Giampaolo Mistura, 1 and CiroSemprebon 21 Department of Physics, University of Padova, Via Marzolo 8, 35131, Padova,Italy2 Max Planck Institute of Dynamic and Self-Organization, Göttingen, GermanyA very active field of research in matterial science is the realization of surfaces with controlledwettability. By playing with the surface chemical composition and its morphology it is possible tosignificantly enhance its hydrophobic (hydrophilic) character. An essential feature in all of theserealizations is the presence of rough surface. The experiments indicate that contact angle behavioris determined by interactions between the liquid and the solid at the three phase contact line aloneand that the interfacial area within the contact perimeter is irrelevant. In this context, understandingthe pinning of the contact line due to morphological defects is essential for the desig of effectivesuperhydrophobic surface. We present the results [1, 2] of extensive experimental and numericalstudies of the suspension of water drops produced on individual posts of mesoscopic size anddifferent cross-sections. In the case of circular pillars, the drop contact line is pinned to the wholeedge contour until the drop collapse due to the action of gravity. In contrast, on square pillars, thedrop are suspended on the four corners and spilling along the vertical walls is observed. We havealso studied the ability of the two geometries to substain drops and found that if we compare pillarswith the same characteristic size, the square is more efficient in pinning large volumes, while if wenormalize the volumes to pillar area, the opposite is true.[1] C. Semprebon, G. Mistura, E. Orlandini, G. Bissacco, A. Segato, J. M. Yeomans, Langmuir 25,5619-5625 (2009).[2] T. Tóth, D. Ferraro, E. Chiarello, M. Pierno, G. Mistura, G. Bissacco, C. Semprebon, Langmuir27, 4742-4748 (2011).117