Dynamic Measurements of Adhesive Contact with a Soft Gel

Establishing a new adhesive contact is a highly dynamic process. The strong drive to conform into contact can rapidly deform a soft, sticky substrate, even when the contact is made quasi-statically. In compliant gels, establishing an adhesive contact may be governed by a complex interplay between adhesive, elastic, and capillary forces interacting with both viscoelastic and poroelastic dissipation mechanisms. We report a series of experiments designed to capture the three-dimensional evolution of a nascent adhesive contact between a compliant silicone gel and a rigid spherical indenter. We use interference, brightfield, and confocal microscopy, respectively, to directly measure the 3D, time-dependent deformation of the gel surface from high-speed sub-micrometer deformations at the initiation of contact to longer-time structural equilibration on the scale of tens of micrometers. These results provide new insights into the governing physics of dynamic adhesion across a broad range of length and time scales.