Self-similarity of contact line depinning from textured surfaces

• Published in: Nature communications Vol. 4; no. 1; p. 1492
• Main Authors: Paxson, Adam T., Varanasi, Kripa K.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.02.2013; Nature Publishing Group; Nature Pub. Group
• Subjects: 639/766/189; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms2482

The mobility of drops on surfaces is important in many biological and industrial processes, but the phenomena governing their adhesion, which is dictated by the morphology of the three-phase contact line, remain unclear. Here we describe a technique for measuring the dynamic behaviour of the three-phase contact line at micron length scales using environmental scanning electron microscopy. We examine a superhydrophobic surface on which a drop’s adhesion is governed by capillary bridges at the receding contact line. We measure the microscale receding contact angle of each bridge and show that the Gibbs criterion is satisfied at the microscale. We reveal a hitherto unknown self-similar depinning mechanism that shows how some hierarchical textures such as lotus leaves lead to reduced pinning, and counter-intuitively, how some lead to increased pinning. We develop a model to predict adhesion force and experimentally verify the model’s broad applicability on both synthetic and natural textured surfaces. The motion of liquid drops on surfaces is governed by adhesion forces, but the microscopic mechanism is unclear. Paxson et al . image the dynamic distortion of the edge of a droplet as it moves across a surface, allowing them to predict the wetting ability of different hierarchically textured surfaces.