Coefficient of restitution for silver nanoparticles colliding on a wet silver substrate

Abstract

Air humidity can intervene in a particle–surface collision by forming a layer of water molecules on the surface. These water molecules act as a buffer layer that alters the collision condition. In this work, we study the effects of condensed water layer on the collision of 5-nm particles on a substrate by molecular dynamics simulations. The coefficient of restitution that is inversely proportional to the adhesion between the nanoparticle and the surface is used to characterize the collision. Results indicate that air humidity can either increase or decrease the coefficient of restitution in the studied nanoscale collisions, depending on the condensed water layer thickness and the surface energy of the substrate. The surface energy of the substrate varies with its Lennard-Jones potential. For a high surface energy substrate, the coefficient of restitution first increases then decreases by increasing the water layer thickness on the substrate when the impact velocity changes from 20 to 500 m/s. For a low surface energy substrate, the coefficient of restitution decreases because of a condensed water layer on the substrate at impact velocities less than 300 m/s. For higher impact velocities, the coefficient of restitution first increases, then decreases, with the condensed water layer thickness.