Molecular dynamics simulations of head-on low-velocity collisions between particles. II. Temperature dependence.

Abstract

Molecular dynamics (MD) simulations have demonstrated that viscous effects arising from thermal motion and molecular rearrangement play a substantial role in collisions between submicron-sized particles. However, most of these simulations have been conducted at fixed temperatures, and the influence of temperature has not been specifically evaluated. In this study, we perform MD simulations of head-on collisions between particles with a radius of 30 nm to examine the temperature dependence of collisions at impact velocities below a few percent of the sound velocity. The results indicate that the coefficient of restitution decreases with increasing temperature, demonstrating that high-temperature collisions cause considerable dissipation of the particles' kinetic energy. We further find that the hysteresis of the interparticle force and contact radius-the difference between the loading and unloading phases-increases with temperature and accounts for the observed temperature dependence of the coefficient of restitution. This hysteresis is attributable to atomic rearrangement: at higher temperatures, stronger atomic random motion promotes more frequent rearrangement. Compression at the contact area forces atoms outward, producing cracks throughout the particles and expanding the contact area. These processes lead to plastic deformation, indicating that greater energy dissipation occurs through plastic deformation at higher temperatures. Atoms that enlarge the contact area also contribute to the attractive force between particles, further enhancing the hysteresis. Finally, we also validate the stress-dependent dissipation model developed in our previous study by fitting it to the MD simulation results and show that the model successfully reproduces the MD simulation.