Experimental Analysis of Dynamic Interactions between Micrometer-Scale Stainless Steel Spheres

The quasi-static interactions between macroscopic, spherical particles are well described by the Hertzian contact law. However, little is known about the interaction law at the micrometer scale, where the effects of electrostatic and hydrodynamic forces at the contact are no longer negligible. Contact dynamics at the micrometer scale have been relatively unexplored due to experimental challenges, since the particles are too small in size to be excited by actuators but too massive to be manipulated by electromagnetic fields. In this work, we experimentally study the dynamic interactions between two micrometer-scale spheres colliding in a v-shaped groove. From our experiments we determine physical parameters of interest that inform us about the force laws that apply before, during and after the collision. These parameters include the coefficient of air resistance, the coefficient of friction between the spheres and the groove, the coefficient of friction between two spheres in contact, and the coefficient of restitution