Physical constraints lead to parallel evolution of micro- and nanostructures of animal adhesive pads: a review

• Thies H. Büscher and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2021, 12, 725–743, doi:10.3762/bjnano.12.57

• convergent results. In the next subsections we discuss the following functional principles: (1) Adaptation to fractal substrate surfaces due to hierarchical organization and thin surface layer, (2) micro- and nanostructural surface pattern and contact splitting, (3) pad material (structure) that is soft

• , reduced due to the reduced ability to form a close contact with rough substrata. Surface pattern and contact splitting The function of hairs/setae in hairy pads is partially discussed in the previous paragraphs. Comparative studies on different animal groups comprising hairy attachment pads reveal

• correlations between the morphometric features of the setal tips and the weight of these animals (Figure 6C): heavier animals possess smaller terminal contact elements, which are also more densely packed [247]. Contact splitting can be used to explain this scaling effect: following this principle, the adhesion

Contact splitting in dry adhesion and friction: reducing the influence of roughness

• Jae-Kang Kim and
• Michael Varenberg

Beilstein J. Nanotechnol. 2019, 10, 1–8, doi:10.3762/bjnano.10.1

• , stronger adhesion, and a more uniform stress distribution with higher tolerance to defects. However, while it is widely believed that contact splitting helps to mitigate the negative effects of roughness on adhesion- and friction-based attachment, no decisive experimental validation of this hypothesis has

• more easily to the surface waviness and by reducing the effective average peeling angle. These findings can be used to guide the development of biomimetic shear-actuated adhesives suitable for operation not only on smooth but also on rough surfaces. Keywords: biomimetics; contact splitting; gecko

• surfaces, stronger adhesion, and more uniform stress distribution with higher tolerance to defects [30][31][32][33][34][35]. However, although it is generally believed that contact splitting helps to mitigate the negative effects of roughness on adhesion- and friction-based attachment [23][30][32], no

Adhesive contact of rough brushes

• Qiang Li and
• Valentin L. Popov

Beilstein J. Nanotechnol. 2018, 9, 2405–2412, doi:10.3762/bjnano.9.225

• structure and an elastic half-space is numerically simulated using the fast Fourier transform (FFT)-based boundary element method and the mesh-dependent detachment criterion of Pohrt and Popov. The problem is of interest in light of the discussion of the role of contact splitting in the adhesion strength of

• gecko feet and structured biomimetic materials. For rigid brushes, the contact splitting does not enhance adhesion even if all pillars of the brush are positioned at the same height. Introducing statistical scatter of height leads to a further decrease of the maximum adhesive strength. At the same time

• modification due to finite size effect of the brush. Keywords: adhesion; brushes; contact splitting; pressure sensitive adhesion; roughness; Introduction The study of adhesive contacts has been largely enhanced by studies of the extremely effective adhesion pads of geckos [1]. For example, the adhesion can

Dry adhesives from carbon nanofibers grown in an open ethanol flame

• Christian Lutz,
• Julia Syurik,
• C. N. Shyam Kumar,
• Christian Kübel,
• Michael Bruns and
• Hendrik Hölscher

Beilstein J. Nanotechnol. 2017, 8, 2719–2728, doi:10.3762/bjnano.8.271

• GPa [30]. CNTs act similarly to the hairs of a Gecko, due to their diameters in the nanometer-range, they can bend quite easily when getting in contact with a rough surface. This effect enables effective contact splitting [31], which leads to an increased contact area, resulting in a high adhesion

• a maximum adhesion energy of 75 fJ at a preload force of 4 μN. Randomly oriented CNFs show a maximum adhesion energy of 47 fJ at a preload force of 3.4 μN. This can be explained with the contact-splitting theory [31] stating that adhesion rises with the number of contacts per area. From SEM images

Stiffness of sphere–plate contacts at MHz frequencies: dependence on normal load, oscillation amplitude, and ambient medium

• Jana Vlachová,
• Rebekka König and
• Diethelm Johannsmann

Beilstein J. Nanotechnol. 2015, 6, 845–856, doi:10.3762/bjnano.6.87

• can be explained by nanoroughness. In other words, contact splitting (i.e., a transport of shear stress across many small contacts, rather than a few large ones) can be exploited to reduce partial slip. Keywords: contact mechanics; contact splitting; contact stiffness; partial slip; quartz crystal

• crack tip. The load dependence of µ points to yet another benefit of “contact splitting” [40][41]. A large number of small contacts will experience less partial slip (less fretting wear) than a small number of correspondingly larger contacts. A side remark: The agreement between the two friction

• by the finite radius of the crack tip at the edge of the contact or by nanoscale roughness. These effects are most pronounced for the smallest contacts. Contact splitting can lower the amount of partial slip and fretting wear. Sketch of the mechanisms underlying partial slip. A Hertzian contact under