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

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.