The role of interfacial curvature in controlling the detachment strength of bioinspired fibrillar adhesives

In this paper we investigate the influence of interfacial curvature on the detachment strength and load distribution of bio-inspired fibrillar adhesives subjected to normal loading. Previous investigations unraveled the benefits of backing layer (BL) thickness in counteracting the detrimental load concentration created by interfacial misalignment. However, little attention was dedicated to the role of interfacial curvature on the load distribution and the emerging adhesive strength. Based on the concavity of the curvature and on the BL thickness, the adhesive can detach more easily or develop stronger adhesion, compared to a flat-on-flat contact. Investigating concavity suggests the possibility of controlling the detachment strength of the adhesive via shape-actuation, where curvature can provide adhesive strengthening or ease of detachment. We analyze the curvature-induced strengthening/weakening of the adhesive in combination to BL thickness, interfacial misalignment, and the geometric characteristics of the array of fibrils. We discover that detrimental load concentrations, created by BL interaction and interfacial misalignment, drastically reduce when the curvature prompts larger stretch to the central fibrils. Conversely, when the curvature prompts larger stretch to the peripheral fibrils, load concentrations superpose to the detriment of adhesive strength. Our quantitative analysis provides a design tool for strong and controllable curvature-based adhesives.