Adhesion Failure at 180 000 Frames per Second: Direct Observation of the Detachment Process of a Mushroom-Shaped Adhesive

Lars Heepe, Alexander E. Kovalev, Alexander E. Filippov, and Stanislav N. Gorb

Phys. Rev. Lett. 111, 104301 – Published 5 September 2013

Abstract

Nature has successfully evolved the mushroom-shaped contact geometry in many organisms in order to solve the attachment problem. We studied the detachment process of individual bioinspired artificial mushroom-shaped adhesive microstructures (MSAMSs) resolving the failure dynamics at high spatiotemporal resolution. The experimental data provide strong evidence for a homogeneous stress distribution in MSAMS, which was recently proposed. Our results allow us to explain the advantage of such contact geometry and provide a suggestion for the widely observed mushroom-shaped contact geometry.

Received 30 May 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.104301

Authors & Affiliations

Lars Heepe¹, Alexander E. Kovalev¹, Alexander E. Filippov^1,2, and Stanislav N. Gorb¹

¹Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten 1-9, 24118 Kiel, Germany
²Donetsk Institute for Physics and Engineering of the National Academy of Sciences of the Ukraine, Donetsk 34083, Ukraine

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Issue

Vol. 111, Iss. 10 — 6 September 2013

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Images

Figure 1
Detachment of two differently microstructured adhesive tapes. Although similar crack propagation at the global scale is observed, illustrated by the background shading from bright (detachment) to dark (attached), crack propagation is completely different at the local scale (see shading of individual structures). (a) In the flat punch contact geometry adhesive failure starts at the perimeter due to edge stress concentrations (see inset). (b) In the mushroom-shaped contact geometry the thin contact plate eliminates the edge stress concentration leading to a homogeneous stress distribution (see inset) changing the adhesive failure mode.Reuse & Permissions
Figure 2
(a) Schematic of the experimental setup. HC, high-speed camera; LS, light source; BS, beam splitter; L, lens; OI, oil immersion; GS, glass slide; S, sample; M, manipulator. (b) Schematic of the video analysis procedure. Within a whole sequence, pixelwise, the change in intensity $I_{x y}$ is observed. (c) Representative intensity profile for a pixel in which MSAMS was first in direct contact with the glass (low intensity). The gradual increase (transition) in intensity corresponds to the propagation of the crack over the pixel area with a duration of $w_{x y}$ until the contact is lost (high intensity) at $d_{x y}$ .Reuse & Permissions
Figure 3
Normalized contact area of MSAMSs 1–3 as a function of time $t$ . Data were obtained from individual frames of high-speed video recordings at $5400 frames / s$ . The very moment of detachment could not be properly resolved as indicated by the sharp transition (dashed box). The decrease in contact area was almost entirely due to shrinkage without losing contact (see still images).Reuse & Permissions
Figure 4
(a),(b),(c) MSAMS 1, 2, 3 in contact with the glass (dark area), respectively. Contact below the stalk appears darker indicated by the dashed line in (a). Sample 1 (a) had a PC outside the contact area below the stalk. Sample 3 (c) as well had a PC, but within the contact area below the stalk. (d),(e),(f) Color-coded $D (x, y)$ of samples 1, 2, 3, respectively. Blue regions detached first, red regions detached last, and areas sharing the same color detached at the same time. (g),(h),(i) Color-coded $V (x, y)$ of samples 1, 2, 3, respectively. Scale bar of $10 μ m$ applies to all images.Reuse & Permissions
Figure 5
(a),(b),(c) Contact area $A$ (filled symbols) and average crack velocity $⟨ v ⟩$ (open symbols), shown from the moment of crack nucleation to complete separation, obtained from the data shown in Fig. 4 for samples 1, 2, 3, respectively. Actual detachment durations were 67, 656, and $2672 μ s$ for samples 1, 2, 3, respectively. Dashed lines correspond to the critical dynamic crack size $a_{c}$ predicted by Eq. (2).Reuse & Permissions

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