Optimizing Adhesive Design by Understanding Compliance

Abstract

Adhesives have long been designed around a trade-off between adhesive strength and releasability. Geckos are of interest because they are the largest organisms which are able to climb utilizing adhesive toepads, yet can controllably release from surfaces and perform this action over and over again. Attempting to replicate the hierarchical, nanoscopic features which cover their toepads has been the primary focus of the adhesives field until recently. A new approach based on a scaling relation which states that reversible adhesive force capacity scales with (A/C)(1/2), where A is the area of contact and C is the compliance of the adhesive, has enabled the creation of high strength, reversible adhesives without requiring high aspect ratio, fibrillar features. Here we introduce an equation to calculate the compliance of adhesives, and utilize this equation to predict the shear adhesive force capacity of the adhesive based on the material components and geometric properties. Using this equation, we have investigated important geometric parameters which control force capacity and have shown that by controlling adhesive shape, adhesive force capacity can be increased by over 50% without varying pad size. Furthermore, we have demonstrated that compliance of the adhesive far from the interface still influences shear adhesive force capacity. Utilizing this equation will allow for the production of adhesives which are optimized for specific applications in commercial and industrial settings.

High strength reversible adhesive closures

“…We can calculate the compliance of an adhesive loop closure, by summing the compliance of each individual component of the system . The adhesive loop is composed of three components, a soft elastomer “pad,” a composite “skin,” and a fabric “tendon.” The elastomer pad, of thickness, t e , width, w , length, L e , and modulus, E e , primarily undergoes shear for thin samples tested here, such that …”

“…Here, we show that this scaling parameter also applies when both sides of the interface contribute compliance. Furthermore, we have shown that ( A/C ) 1/2 can be calculated by superposition of the mechanical properties of individual components . An equation was derived specifically to calculate the generalized reversible adhesive scaling parameter for adhesive closures, and again ( A/C ) 1/2 was calculated accurately.…”

“…Samples were created in a similar manner as described in previous publications . Briefly, the system consists of two materials, fabric and elastomer.…”

“…The elastomer storage moduli were 3.1 MPa for ST1060, 1.0 MPa for ST3040, and 0.4 MPa for F15. The elastomers exhibited little rate dependence except at high frequency, likely making the mechanical properties of the adhesive closures rate independent . Four fabrics were used; 24K unidirectional carbon fiber tape with a nominal thickness of 0.3 mm was purchased from Soller Composites, 3K carbon fiber/Kevlar composite fabric and glass fiber fabric with nominal thicknesses of 0.21 mm and 0.3 mm were purchased from US Composites, and plain weave nylon fabric with a nominal thickness of 0.2 mm was purchased from Joann Fabrics (Hadley, MA).…”

“…Samples were created in a similar manner as described in previous publications. 28,32 Briefly, the system consists of two materials, fabric and elastomer. The elastomers consisted of commercially available two-part polyether-based polyurethane elastomers purchased from BJB Enterprises.…”