SUMMARY We describe a general, linearized fracture mechanics analysis for studying the adhesive properties of elastic, low modulus materials. Several adhesion tests are described, but all involve an elastic material which is brought into contact with a rigid surface along an axis of radial symmetry. Relationships between the load, displacement, and radius of the circular contact area between the two materials are described. These relationships involve the elastic modulus of the compliant material, the energy release rate (or adhesion energy) and various parameters which characterize the geometry of interest. The ratio of the contact radius to the thickness of the elastic material is shown to be a particularly important parameter. After reviewing some general concepts relevant to the adhesion of soft polymeric materials, we describe the fracture mechanics analysis, and provide examples from our own work on the adhesion of elastomers, thermoreversible gels and pressure sensitive adhesives.

We describe a general, linearized fracture mechanics analysis for studying the adhesive properties of elastic, low modulus materials. Several adhesion tests are described, but all involve an elastic material which is brought into contact with a rigid surface along an axis of radial symmetry. Relationships between the load, displacement, and radius of the circular contact area between the two materials are described. These relationships involve the elastic modulus of the compliant material, the energy release rate (or adhesion energy) and various parameters which characterize the geometry of interest. The ratio of the contact radius to the thickness of the elastic material is shown to be a particularly important parameter. After reviewing some general concepts relevant to the adhesion of soft polymeric materials, we describe the fracture mechanics analysis, and provide examples from our own work on the adhesion of elastomers, thermoreversible gels and pressure sensitive adhesives.

ABSTRACT:In this article we use a linear elastic fracture mechanics approach to characterize the adhesive performance of two commercially available pressure-sensitive adhesives (PSAs). An axisymmetric adhesion test involving the contact of a spherical indenter with a thin adhesive layer is used to generate "tack" curves for both adhesives. These curves describe the relationship between the normal loads and displacements during the test. Adhesive failure is understood in terms of crack propagation at the indenter/adhesive interface. We investigate the effects of adhesive layer thickness and crosshead velocity on the tack curves. Using fracture mechanics equations developed for thin layers, we show that the energy release rate is a unique function of the crack velocity for a given adhesive. Based on the tack curves and energy release rates, we discuss the coupling of the bulk and interfacial properties that produce the large adhesion energies typical of pressure-sensitive adhesives.

In this article we use a linear elastic fracture mechanics approach to characterize the adhesive performance of two commercially available pressure‐sensitive adhesives (PSAs). An axisymmetric adhesion test involving the contact of a spherical indenter with a thin adhesive layer is used to generate “tack” curves for both adhesives. These curves describe the relationship between the normal loads and displacements during the test. Adhesive failure is understood in terms of crack propagation at the indenter/adhesive interface. We investigate the effects of adhesive layer thickness and crosshead velocity on the tack curves. Using fracture mechanics equations developed for thin layers, we show that the energy release rate is a unique function of the crack velocity for a given adhesive. Based on the tack curves and energy release rates, we discuss the coupling of the bulk and interfacial properties that produce the large adhesion energies typical of pressure‐sensitive adhesives. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3455–3472, 1999

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.