Detachment of compliant films adhered to stiff substrates via van der Waals interactions: role of frictional sliding during peeling

Abstract

The remarkable ability of some plants and animals to cling strongly to substrates despite relatively weak interfacial bonds has important implications for the development of synthetic adhesives. Here, we examine the origins of large detachment forces using a thin elastomer tape adhered to a glass slide via van der Waals interactions, which serves as a model system for geckos, mussels and ivy. The forces required for peeling of the tape are shown to be a strong function of the angle of peeling, which is a consequence of frictional sliding at the edge of attachment that serves to dissipate energy that would otherwise drive detachment. Experiments and theory demonstrate that proper accounting for frictional sliding leads to an inferred work of adhesion of only approximately 0.5 J m 22 (defined for purely normal separations) for all load orientations. This starkly contrasts with the interface energies inferred using conventional interface fracture models that assume pure sticking behaviour, which are considerably larger and shown to depend not only on the mode-mixity, but also on the magnitude of the mode-I stress intensity factor. The implications for developing frameworks to predict detachment forces in the presence of interface sliding are briefly discussed.

Grasping Without Squeezing: Design and Modeling of Shear-Activated Grippers

“…Tape peeling models that incorporate stretch and slip are quite relevant [27], [28], however they do not consider the cases where the peel angle is zero, or when the slip zone is much larger than the thickness of the tape, as in the present case. In creating a model capable of including both slipping and stretching of a film while pulled along a surface, we assume pulling along a flat surface for simplicity.…”

Continuum contact models for coupled adhesion and friction

“…Some of these models also incorporate sliding friction. As experiments show, approaches of this type are suitable to accurately capture the peeling force of structures with small bending stiffness such as elastomer films [26], adhesive tape [28], and adhesive beetle pads [62]. These models are thus often applied to discuss the properties of bio-adhesive systems.…”

Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

“…As the pads changed from static to dynamic contact, sliding of the entire pad was likely preceded by partial slippage close to the peel front. Such interfacial slippage can lead to a profound increase in the apparent strain energy release rate [20,21,22,18,23], as sliding 'consumes' part of the available energy, so that eqs. 1 and 2 are no longer valid.…”

“…In fracture mechanics, G is often modelled as a function of 'mode-mixity', i. e. the extent to which interfacial failure occurs via shear versus tensile stresses (e. g. [32,33]). For tape peeling, however, the mode-mixity dependence of G may largely arise from frictional 'dissipation' [18,23], and is thus unlikely to provide an explanation (see above). Instead, the 'true' tensile strength of the interface must increase.…”