Characterization of the contact dynamics of spheres coated in a thin viscous film using an electrified Newton's cradle

Measurement of the contact time for two spheres coated in a thin viscous film are considered. Measurements are performed using a Newton's cradle apparatus with a current passed through the apparatus such that the voltage can be used to infer the separation between the spheres. The spheres are coated with either a nonconductive viscous liquid (silicone oil) or a conductive liquid (glycerol and KCl). Measurement of the sphere-film contact time and sphere-sphere contact time for different film thicknesses and precollisional velocities are presented. Measurements of these contact times are compared to numerical simulations using the discrete element method (DEM). The results indicate that a solid-solid contact is the physical mechanism which dictates rebound. A viscous force model where the interstitial liquid undergoes a glass transition was found to represent the dynamics of the system well, despite no glass transition being observed.