Pinning-depinning of the contact line on nanorough surfaces
Laboratoire de Physique de la Matière Condensée et Nanostructures (UMR 5586), Université Claude Bernard Lyon 1 et CNRS - Domaine Scientifique de la Doua, 69622, Villeurbanne Cedex, France
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Accepted: 25 January 2006
Published online: 10 April 2006
We study the pinning-depinning phenomenon of a contact line on a solid surface decorated by a random array of nanometric structures. For this purpose, we have investigated the contact angle hysteresis behaviour of six different wetting and non-wetting fluids with surface tensions varying from 25 to 72mN m^-1. For low values of the areal density of defects φd, the hysteresis H increases linearly with φd indicating that “individual” defects pin the contact line. Then, from a given value of φd, the hysteresis H becomes to decrease with increasing φd, indicating a new kind of collective depinning. These two regimes were observed for all fluids used. In both cases, our experimental results are compared with the theoretical predictions for contact angle hysteresis induced by single or multiple topographical defects. We ascribe the decrease of H to the formation of cavities along the wetting front.
PACS: 68.08.Bc Wetting – / 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions – / 61.46.-w Nanoscale materials –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2006