Scaling normal adhesion force capacity with a generalized parameter.

The adhesive response of a rigid flat cylindrical indenter in contact with a compliant elastic layer of varying confinement is investigated experimentally and described analytically. Using a soft elastic gel with substrate thickness, t, and indenter radius, a, 28 unique combinations of the confinement parameter, a/t, are examined over a range of 0.016 < a/t < 7.2. Continuous force capacity predictions as a function of a/t and material properties are provided through a scaling theory and are found to agree well with the experimental data. We further collapse all of the data over orders of magnitude in adhesive force capacity onto a single line described by a generalized reversible adhesion scaling parameter, A/C, where A is the contact area and C is the compliance. As the scaling analysis does not assume a specific separation mechanism the adhesive force capacity is well described during both axisymmetric edge separation and during interfacial fingering and cavitation instabilities. We discuss how the geometry of the contact, specifically increasing the degree of confinement, allows reversible adhesive materials to be designed that are not "sticky" or "tacky", yet can be very strong and provide high performance.