Functional Adhesive Surfaces with “Gecko” Effect: The Concept of Contact Splitting

Abstract

Nature has developed reversibly adhesive surfaces whose stickiness has attracted much research attention over the last decade. The central lesson from nature is that “patterned” or “fibrillar” surfaces can produce higher adhesion forces to flat and rough substrates than smooth surfaces. This paper critically examines the principles behind fibrillar adhesion from a contact mechanics perspective, where much progress has been made in recent years. The benefits derived from “contact splitting” into fibrils are separated into extrinsic/intrinsic contributions from fibril deformation, adaptability to rough surfaces, size effects due to surface‐to‐volume ratio, uniformity of stress distribution, and defect‐controlled adhesion. Another section covers essential considerations for reliable and reproducible adhesion testing, where better standardization is still required. It is argued that, in view of the large number of parameters, a thorough understanding of adhesion effects is required to enable the fabrication of reliable adhesive surfaces based on biological examples.

Numerical implementation of multiple peeling theory and its application to spider web anchorages

“…It is well known [7,8] that a larger number of contacts occurring in the pyriform silk implies a greater peeling line, and, therefore, a higher delamination strength. However, we will show in this section that other mechanisms related to the architecture of the anchorages can explain the differences between their different behaviour and maximal pull-off force.…”

“…Gecko adhesion, which is based on van der Waals forces, achieves strengths of up to 1 MPa through the contact of billions of spatulae for each foot pad [5,6]. As in other cases of natural adhesives, the key to strong adhesion seems to lie in their hierarchical structure, which allows good adaptation to the surface and repeated contact splitting to increase the total peeling line without selfbunching [7,8]. The observation of these natural structures has inspired the design and realization of artificial dry adhesives (i.e.…”

Funnel‐Shaped Microstructures for Strong Reversible Adhesion

“…[7,[13][14][15][16] Patterned surfaces can exhibit better adhesion compared to nonpatterned counterparts, e.g., due to a higher compliance and, therefore, reduced elastic strain energy penalties and a higher conformability to various substrate topographies; these benefits have been termed the "contact splitting" effect. [2,17,18] The adhesion relies mainly on van der Waals interactions across the pattern-substrate interface. In addition, capillary forces may support the adhesive interaction.…”

Fibrillar Elastomeric Micropatterns Create Tunable Adhesion Even to Rough Surfaces

“…[6][7][8][9][10][11] There are several studies that have demonstrated and characterized the adhesion of gecko-inspired micropatterned surfaces on hard, smooth substrates (for reviews see, for instance, refs. [12][13][14][15][16][17][18][19] ). However, considering that all natural and almost all artifi cial surfaces have a roughness on one or more different length scales, little research has been conducted to comprehend and optimize the adhesion of such structures to rough surfaces.…”