Impalement of fakir drops

¹  Physique et Mécanique des Milieux Hétérogènes, UMR 7636 du CNRS, ESPCI - 75005 Paris, France
²  The Rudolf Peierls Centre for Theoretical Physics, University of Oxford - 1 Keble Road, Oxford OX1 3NP, UK

Received: 7 September 2007
Accepted: 19 November 2007

Abstract

Water drops deposited on hydrophobic materials decorated with dilute micro-posts generally form pearls. Owing to the hydrophobicity of the material, the drop sits on the top of the posts. However, this ”fakir state” is often metastable: if the drop impales inside the texture, its surface energy is lowered. Here we discuss the transition between these two states, considering the drop size as a parameter for inducing this transition: remarkably, it is found that a drop impales when it becomes small, which is interpreted by considering its curvature. This interpretation allows us to propose different recipes for avoiding this detrimental effect.