Direct observation of microcavitation in underwater adhesion of mushroom-shaped adhesive microstructure

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

Beilstein J. Nanotechnol. 2014, 5, 903–909, doi:10.3762/bjnano.5.103

• , M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383–385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting

• negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L

• in predominantly liquid environments. Keywords: bio-inspired; biomimetic; cavitation; contact mechanics; gecko; interface; negative pressure; pull-off; surface; tribology; Introduction During the past two decades, bio-inspired microstructured adhesives became a new class of adhesive materials with

The optimal shape of elastomer mushroom-like fibers for high and robust adhesion

• Burak Aksak,
• Korhan Sahin and
• Metin Sitti

Beilstein J. Nanotechnol. 2014, 5, 630–638, doi:10.3762/bjnano.5.74

• mushroom-like fibers is investigated by implementing the Dugdale–Barenblatt cohesive zone model into finite elements simulations. It is found that the magnitude of pull-off stress depends on the edge angle θ and the ratio of the tip radius to the stalk radius β of the mushroom-like fiber. Pull-off stress

• β and θ. An analytical model for pull-off stress, which depends on the location of crack initiation as well as on θ and β, is proposed and found to agree with the simulation results. Results obtained in this work provide a geometrical guideline for designing robust bio-inspired dry fibrillar

• . Furthermore, measured adhesive strengths have matched, and in some instances such as smooth surface applications, surpassed the adhesive strengths recorded for gecko footpads [21][30][33][37]. Work by del Campo et al. [21] reports enhancements in pull-off loads as much as 40-fold with mushroom-like fibers

Hairy suckers: the surface microstructure and its possible functional significance in the Octopus vulgaris sucker

• Francesca Tramacere,
• Esther Appel,
• Barbara Mazzolai and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2014, 5, 561–565, doi:10.3762/bjnano.5.66

• generated in a binary on/off state [14]. These studies also reveal that structured surfaces show a 25% increase in pull-off force when immersed in water, and their underwater attachment is 20 times more effective than that of flat surfaces [15]. The grooves found in the infundibulum area generating a dense

Single-asperity contact mechanics with positive and negative work of adhesion: Influence of finite-range interactions and a continuum description for the squeeze-out of wetting fluids

• Martin H. Müser

Beilstein J. Nanotechnol. 2014, 5, 419–437, doi:10.3762/bjnano.5.50

• ac. Johnson, Kendall, and Roberts (JKR) [6] solved the problem for short-range adhesion, for which the attractive surface forces act directly at the contact line. Unlike Hertz and DMT, JKR found finite values for Ac and d at pull off. Tabor [7] introduced a dimensionless parameter, μT, now known as

• the behavior near pull-off for Δγ > 0. For the latter, it is straightforward to deduce from established results how the ac(FN) relation depends on the Tabor coefficient in the DMT and the JKR limit. Specifically, ac − ap (FN + Fp)κ for FN ≥ −Fp, where Fp and ap are pull-off force and pull-off radius

• , respectively. They both depend on μT just like the exponent κ, e.g., ap > 0 and κ = 1/2 in the JKR limit, while ap = 0 and κ = 1/3 for DMT. In the present comparison of squeeze-out (finite-range repulsion) versus pull-off (finite-range attraction), I also study whether the exponent κ changes continuously

Exploring the retention properties of CaF₂ nanoparticles as possible additives for dental care application with tapping-mode atomic force microscope in liquid

• Matthias Wasem,
• Joachim Köser,
• Sylvia Hess,
• Enrico Gnecco and
• Ernst Meyer

Beilstein J. Nanotechnol. 2014, 5, 36–43, doi:10.3762/bjnano.5.4

• , the tooth enamel, which was mechanically polished before use, had a mean square roughness (RMS) ranging between 3.4–4.0 nm. The higher substrate roughness of enamel would lower the particle–substrate contact area. This has been experimentally verified in earlier studies by measuring the pull-off force

Dynamic nanoindentation by instrumented nanoindentation and force microscopy: a comparative review

• Sidney R. Cohen and
• Estelle Kalfon-Cohen

Beilstein J. Nanotechnol. 2013, 4, 815–833, doi:10.3762/bjnano.4.93

• crosslinking density and chemical surface modifications [80][107][108][109]. The viscoelastic response has been studied both through hysteresis in the loading–unloading portion of the curve [110][111], and in the adhesive pull-off segment [80][109]. Analyzing the results in this fashion allows one to

Ni nanocrystals on HOPG(0001): A scanning tunnelling microscope study

• Michael Marz,
• Keisuke Sagisaka and
• Daisuke Fujita

Beilstein J. Nanotechnol. 2013, 4, 406–417, doi:10.3762/bjnano.4.48

• theory [27]), i.e., in the limit of small deformations. Thus, the adhesive force can be written as where γx is the surface tension and R the radius of the cluster, assuming a spherical particle. With γHOPG = 1.75 J/m2, γNi = 2.45 J/m2, and R = 5.9 nm, a pull off force of Fa = −4.36 nN is expected. The

Switching adhesion forces by crossing the metal–insulator transition in Magnéli-type vanadium oxide crystals

• Bert Stegemann,
• Matthias Klemm,
• Siegfried Horn and
• Mathias Woydt

Beilstein J. Nanotechnol. 2011, 2, 59–65, doi:10.3762/bjnano.2.8

• instantaneously jumps out of contact back into its equilibrium position. The force necessary to pull-off the cantilever represents, to a first approximation, the adhesion force [24][28]. The graphs in Figure 4 provide an analysis of the adhesion forces acquired at the V4O7 cleavage plane at 120 K (i.e., below the

• Johnson–Kendall–Roberts (JKR) model [19]. These two models improved the Hertzian theory [18] by including the effect of adhesion and present the limiting cases of more general contact theories by Maugis [32]. Both models have in common that the pull-off-force is independent of the elastic material

• crystal plane at 120 K and 298 K. The curves show the force interaction during approach and retraction of the tip from the surface. The adhesion force corresponds to the pull-off force between the tip and sample surface. Statistical analysis of the adhesion forces acquired at the V4O7 cleavage plane at (a