Adhesion of Bioinspired Micropatterned Surfaces:  Effects of Pillar Radius, Aspect Ratio, and Preload

Abstract

Inspired by biological attachment systems, micropatterned elastomeric surfaces with pillars of different heights (between 2.5 and 80 microm) and radii (between 2.5 and 25 microm) were fabricated. Their adhesion properties were systematically tested and compared with flat controls. Micropatterned surfaces with aspect ratios above 0.5 were found to be more compliant than flat surfaces. The adhesion significantly increases with decreasing pillar radius and increasing aspect ratio of the patterned features. A preload dependence of the adhesion force has been identified and demonstrated to be crucial for obtaining adhesives with tunable adherence.

Buckling of sheared and compressed microfibrils

“…Inspired by these micro-and nanostructures, many research groups have fabricated synthetic mimics using various polymers or carbon nanotubes to create arrays of microfibrils. Typically, fibrils in these arrays are terminated with either a thin film or a spatula to enhance contact and adhesion (Gorb et al 2006;Kim & Sitti 2006;Aksak et al 2007;del Campo et al 2007;Greiner et al 2007;Reddy et al 2007;Schubert et al 2007). These fibrils are part of a backing layer that is made up of the same material, typically a soft elastomer such as poly(dimethylsiloxane) or polyurethane.…”

Compliance of a microfibril subjected to shear and normal loads

“…Recent interest in bio-inspired adhesives has motivated many researchers to fabricate microfibril arrays (Liu & Bhushan 2003;Peressadko & Gorb 2004;Chung & Chaudhury 2005;Crosby et al 2005;Glassmaker et al 2005Glassmaker et al , 2007Huber et al 2005;Northen & Turner 2005;Yurdumakan et al 2005;Kim & Sitti 2006;Majidi et al 2006;Aksak et al 2007;Gorb et al 2007;Greiner et al 2007; and to study their contact mechanics and adhesion (Jagota & Bennison 2002;Gao et al 2003Gao et al , 2005Persson & Gorb 2003;Hui et al 2004;Persson et al 2005;Spolenak et al 2005a,b;Tang et al 2005;Bhushan et al 2006;Tian et al 2006;Yao & Gao 2006;Chen & Gao 2007). Most of these studies focus on how the interface between the microfibrils and a smooth, hard substrate separates under a normal load.…”

Strength statistics of adhesive contact between a fibrillar structure and a rough substrate

“…Nevertheless, the conclusion of this paper is valid since we are interested in the maximum pull-off force. In practice, the pull-off force can be smaller and will depend on the preload, as demonstrated by Schargott et al (2006), Aksak et al (2007), Greiner et al (2007) and Kim & Bhushan (2007). …”

“…Fabrication of synthetic structures with a high degree of hierarchy is still technologically challenging and most of the fibrillar adhesives fabricated so far are either one-or two-level structures. The one-level structure typically consists of pillars having approximately uniform cross-sections and nominally flat tips (Geim et al 2003;Sitti & Fearing 2003;Glassmaker et al 2004;Gorb et al 2006;Greiner et al 2007). Although these structures typically show an increase in adhesion per unit area of actual contact, the overall adhesion was still less than that of a flat interface.…”