Beetle-inspired adhesion by capillary-bridge arrays: pull-off detachment

Abstract

Adhesion by capillarity (‘wet’ adhesion) depends on the surface tension of an array of many small liquid bridges acting simultaneously against a substrate. A particular leaf beetle has been previously shown to defend itself using wet adhesion, and a man-made device, inspired by this beetle, has been previously demonstrated to exhibit electronically controlled switchable wet adhesion. In both cases, measurements of detachment under load have been reported as pull-off strengths. In this paper, we pose models for pull-off failure of adhesion and discuss the predictions of these models in relationship to available observations. The focus is on the role of array geometry and how net adhesive failure relates to the instability of a single liquid bridge.

Keywords:

• adhesion
• beetle
• liquid bridge
• detachment mechanism

Acknowledgments

The authors would like to thank Tom Eisner and Dan Aneshansley for kindly supplying the photo in Figure 9 and for useful clarifications. The work of John Faria was supported in part by a LIFE grant for undergraduate research funded by Cornell University alumni. Useful discussions with Henrik van Lengerich and Brenton Cox are acknowledged. This work was supported by NSF Grant CBET-0653831 and the Defense Advanced Research Planning Agency.

Notes

In memory of Thomas Eisner, tireless advocate for Nature's largely unread dictionary, who passed away 25 March 2011