Metastable states and activated dynamics in thin-film adhesion to patterned surfaces

Abstract

We consider adhesion due to London-van der Waals attraction between a thin film and a patterned surface with nanometer asperities. Depending on the surface topography and the stiffness of the film, three regimes of adhesion are identified: complete contact adhesion, partial contact adhesion, and glassy adhesion. For complete contact adhesion, the film conforms to the undulations of the surface, whereas for partial contact and glassy adhesion, the adhesive interface breaks down into microscopic areas of contact. When a film in the glassy regime is peeled off the surface, metastable states develop at which the crack front becomes arrested, analogously to the frustrated motion of the three-phase contact line across a heterogeneous surface. For this glassy regime, we use transition state theory to model the thermally activated progression of the crack front. This theoretical treatment suggests that the rate of the adhesive failure increases exponentially with the applied force.

Understanding Surface Adhesion in Nature: A Peeling Model

“…The periodic fibrils topped by a thin plate on the backing enhances the peel strength through periodically variable peel energy . The patterned surface on the substrate also increases the peel force because of crack nucleation or pinning . Simply introducing interlocking linkers can enhance the peel force resulted from increasing adhesion energy …”

“…c,d,e) Various topographies of substrate with flat surface, corrugated surface, and grid of spheres. Adapted with permission . Copyright 2014, American Physical Society.…”

“…There are two parameters controlling the apparent adhesion energy: the period of adhesion energy and the adhesive zone size at substrate. For more systematical analysis, Lindström et al studied a patterned surface with nanometer asperities (Figure c,d,e). By considering the surface geometry and the film stiffness, they identified three adhesion regimes.…”

“…The adhesive interface in the partial contact adhesion is subdivided into microscopic zones of contact. For glassy adhesion, during peeling, the crack front becomes arrested at the metastable states …”

“…Among various adhesion models attempting to describe the actual adhesion, the peeling model has been developed to understand surface adhesion of ants, bees, flies, cockroaches, geckos, frogs, spiders, and so on. As peeling model is approaching to describing the attachment and detachment processes of two adhesive surfaces accurately, it is being regarded as the theoretical foundation to design surface adhesive materials including modulating the topography of two surfaces, adding the interfacial linkers . What is more, peeling is an interesting and ubiquitous process in biological and artificial adhesive systems.…”