The effect of surface geometry on collisions between nanoparticles

In this molecular dynamics study, we examine the local surface geometric effects of the normal impact force between two approximately spherical nanoparticles that collide in a vacuum. Three types of surface geometries, facets, sharp crystal edges, and amorphous surfaces of nanoparticles with radii R < 10 nm are considered, and the impact force is compared with its macroscopic counterpart described by a nonlinear contact force, FN proportional to D with n = 3/2 derived by Hertz (1881), where D is the overlap induced by elastic compression. We study the surface geometry-dependent impact force. For facet-facet impact, the mutual contact surface area does not expand due to the large facet surface, and this in turn leads to a non-Hertz impact force, n < 3/2. A Hertz-like contact force, n = 1.5, is recovered in the edge contact and in the amorphous surface contact, allowing expansion of the mutual contact surface area. The results suggest that collisions of amorphous nanoparticles or nanoparticles with sharp edges may maintain dynamic phenomena, such as breathers and solitary waves, originating from the nonlinear contact force.