(689e) Dynamic of Flooded Adhesion in the Presence of Draining Channels

We will discuss our efforts to understand the mechanisms behind the adhesion of the tree frog under wet conditions. Central to the adhesion and locomotion of tree frogs is their structured toe pads, which consist of hexagonal arrays of epithelial cells separated by a network of interconnected channels. It has been proposed that the channels facilitate the drainage of excess fluid trapped between the toe pads and the contacting surface, and thus reduce the hydrodynamic repulsion during approach. We present direct force measurements of the normal and peeling hydrodynamic interactions during the drainage of fluid from the gap between a structured and a smooth surface using surface force apparatus. We investigate two limits: when the interacting surfaces are driven toward each other at constant velocity and constant force. We compare our results to predictions from Reynolds’ theory and discuss how the deviations are related to the surface features. We find agreement between our experiments and the scaling analysis for Reynolds theory in the limit where fluid can drain through the structure.