Adhesion of compliant spheres: An experimental investigation

The detachment of soft adhesive spheres is strongly affected by the displacement rate. Nonetheless, the classical Johnson, Kendall & Roberts (JKR) theory is usually adopted to describe both the loading and unloading process, with the implicit assumption of defining different values of the elastic modulus and interfacial adhesion energy for the two phases. In this work, we use a different approach to model the unloading phase, usually characterized by viscoelastic dissipation. Specifically, experimental data are fitted with the numerical model proposed by Muller for the contact of viscoelastic spheres. In such way, by exploiting a mixed JKR-Muller model, we are able to quantify the energy loss due to elastic and viscoleastic adhesion hysteresis. Moreover, we find that the pull-off force is order of magnitude larger than the JKR prediction and increases with the detachment rate, while the effect of the maximum load reached before unloading is, as expected, negligible.