We will discuss our efforts to understand the mechanisms behind the adhesion of 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. We find that the structured surfaces lead to faster time to contact due to the reduction of drainage forces and can display stronger adhesion. We compare to our results with that of Reynolds theory modified for structured surfaces. ReferencesR.  Gupta and J. Frechette *, �Interferometry of surfaces with well-defined topography in the surface force apparatus�, Journal of Colloid and Interface Science, 412, 82-88, 2013.R. Gupta and J. Frechette* , �Measurement and scaling of hydrodynamic interactions in the presence of draining channels�, Langmuir, 28, 14703-14712, 2012.

Lubrication and wet adhesion in the presence of draining channels

247th National Meeting (2014)

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