Friction and Adhesion of Gecko-Inspired PDMS Flaps on Rough Surfaces

Abstract

Geckos have developed a unique hierarchical structure to maintain climbing ability on surfaces with different roughness, one of the extremely important parameters that affect the friction and adhesion forces between two surfaces. Although much attention has been paid on fabricating various structures that mimic the hierarchical structure of a gecko foot, yet no systematic effort, in experiment or theory, has been made to quantify the effect of surface roughness on the performance of the fabricated structures that mimic the hierarchical structure of geckos. Using a modified surface forces apparatus (SFA), we measured the adhesion and friction forces between microfabricated tilted PDMS flaps and optically smooth SiO(2) and rough SiO(2) surfaces created by plasma etching. Anisotropic adhesion and friction forces were measured when sliding the top glass surface along (+y) and against (-y) the tilted direction of the flaps. Increasing the surface roughness first increased the adhesion and friction forces measured between the flaps and the rough surface due to topological matching of the two surfaces but then led to a rapid decrease in both of these forces. Our results demonstrate that the surface roughness significantly affects the performance of gecko mimetic adhesives and that different surface textures can either increase or decrease the adhesion and friction forces of the fabricated adhesives.

Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

“…First, the rough surfaces exhibit the highest friction forces and stick-slip magnitude. This can be explained through an interlocking mechanism [33] (figure 6) where the roughness of the surface matches with the interspacing of the array of flaps. Based on the values in table 1, the average distance between asperities on the rough surface (6.7 + 3.5 mm) shows that it is possible to fit the flap dimensions (10 mm  3.5 mm) in between some spots where the asperities are more spread out.…”

“…properties of a gecko footpad were fabricated and have been described elsewhere [16,33]. A modified SFA (SurForce LLC) [16,43] was used to measure the normal F ?…”

“…The slip times are dependent on the elastic material properties of the flap's surface, where they are equivalent regardless of the surface roughness. These characteristic length and time scales give rise to a stick-slip sliding behaviour that is less reliant on the commensurability between the shearing surfaces; however, the surface commensurability is a crucial property that determines the magnitude of friction (and adhesion) forces [33]. While shearing the PDMS microflaps against the silica surfaces (both smooth and rough), f s 2 f k decreased and f k increased as v was increased (figure 4 …”

Multiscale Frictional Properties of Cotton Fibers: A Review

“…Specifically, the tribological properties of conventional bulk plastics [35][36][37][38], rubber-like materials [39], fiber-reinforced composites [40], polymer nanocomposites [41][42][43], cross-linked hydrogels [44], end-grafted polymers (a.k.a. polymer brushes) [45], mammalian articular joints [46], gecko-inspired surfaces [47], and mussel-inspired coatings [48] have been investigated. For viscoelastic solids, such as polymers, it has been shown that friction is velocity-dependent and Equation (1) cannot be valid over a wide range of sliding velocities.…”

The effect of substrate roughness on tape peeling

“…Their model predicts the peeling behavior of adhesive tapes from a glass substrate at peel angles at 90°or less without considering substrate roughness. Pesika's PZ model adds an angle-dependent multiplier to the Kendall equation [8]. A more widely applicable PZ model including large deformation and pre-strain of the backing layer was presented by Molinari and Ravichandran [5].…”