Effects of surface roughness and film thickness on the adhesion of a bioinspired nanofilm

Abstract

Inspired by the gecko's climbing ability, adhesion between an elastic nanofilm with finite length and a rough substrate with sinusoidal roughness is studied in the present paper, considering the effects of substrate roughness and film thickness. It demonstrates that the normal adhesion force of the nanofilm on a rough substrate depends significantly on the geometrical parameters of the substrate. When the film length is larger than the wavelength of the sinusoidal roughness of the substrate, the normal adhesion force decreases with increasing surface roughness, while the normal adhesion force initially decreases then increases if the wavelength of roughness is larger than the film length. This finding is qualitatively consistent with a previously interesting experimental observation in which the adhesion force of the gecko spatula is found to reduce significantly at an intermediate roughness. Furthermore, it is inferred that the gecko may achieve an optimal spatula thickness not only to follow rough surfaces, but also to saturate the adhesion force. The results in this paper may be helpful for understanding how geckos overcome the influence of natural surface roughness and possess such adhesion to support their weights.

Effects of surface wettability on gecko adhesion underwater

“…Experimental and theoretical studies on gecko adhesion mechanisms have been carried out extensively during the past decades, most of which mainly focus on the van der Waals adhesion mechanism on dry solid surfaces [5,[8][9][10][11]. However, there are more than 1400 species of geckos in the world and different species possess different natural habitats and living conditions [12].…”

Effect of pre-tension on the peeling behavior of a bio-inspired nano-film and a hierarchical adhesive structure

“…It is shown that, for a determined pre-tension, the effective adhesion energy of the second level is improved at small peeling angles, while it is reduced at relatively large ones. As discussed in one of our previous works, 18 the adhesion force of a structure is almost linearly proportional to the effective adhesion energy. Therefore, pre-tension in the first level also improves the adhesion force of the hierarchical structure at small peeling angles, while reduces it at large ones as shown in Fig.…”

“…The adhesive behavior of a bio-inspired nano-film with a finite contact length was investigated by Peng et al, 12 in which the effect of the adhesive length on adhesion force was considered. The influences of surface roughness 18 and environmental relative humidity 6 on nano-film's adhesion were further studied. All the above theoretical results are helpful to explain some existing experimental observations of geckos' adhesion, such as the size effect of a spatula and the rolling behavior of geckos' feet for reversible adhesion.…”

Sticking to the story: outstanding challenges in gecko-inspired adhesives

“…Work in the laboratory, as well as with freeranging geckos, has explored the effects of surface roughness on adhesion and synthetic design in only limited ways, probably because roughness is a deceptively complex parameter; real surfaces vary in roughness over many length scales, making the characterization of roughness non-trivial (Persson and Gorb, 2003). Basic theory and laboratory work on the effects of controlled roughness on gecko adhesion (Persson and Gorb, 2003;Huber et al, 2007;Persson, 2007;Greiner et al, 2009;Peng and Chen, 2011) have made an important contribution to our thinking about the design of the gecko adhesive system, especially as it relates to safety factors (Pugno and Lepore, 2008;Russell and Johnson, 2014). Safety factors in a system reflect the capacity of that system to perform beyond expected or normal limits in ideal circumstances (Hawkes et al, 2015).…”