Sticking and restitution in collisions of charged sub-mm dielectric grains

Abstract

In microgravity experiments, dielectric spherical glass grains of 225 μm radius with electrical charges between 105 e and 107 e collide with a metal wall. Collision velocities range from about 0.01 m/s up to 0.2 m/s. Grains rebound from the wall down to a threshold impact velocity below which particles stick. This threshold velocity for sticking increases linearly from below 0.01 m/s to 0.15 m/s with increasing charge on the grains. This can be explained by non-homogeneous surface charges on the grains and mirror charges on the metal wall. The Coulomb attraction boosts the grain speed just prior to impact. This increases the energy dissipated upon impact, and grains can no longer escape the Coulomb field of the mirror charge if they are too slow. For rebounding particles, the final boost decreases the measurable, effective coefficient of restitution and induces a wide spread.