A molecular dynamics study on the collisional dynamics of soft and sticky single face-centered cubic crystal nanoparticles is presented. The softness and stickiness of the nanoparticles are controlled by varying parameters in the Lennard-Jones potential that is used to describe the interatomic interactions. Softening of nanoparticles due to extensive plastic deformations is observed as was previously found in hard nanoparticles. Further, two primary plastic deformation modes, slip and twinning, of the nanoparticles are found to play important roles in the temperature dependence of the coefficient of restitution. Additionally, we observe the effects of surface roughness, facets, and edges in the collisional behaviors of the sticky nanoparticles in low-velocity collisions. Nevertheless, the Johnson-Kendall-Roberts theory for macroscopic adhesive bodies still remains valid in nearly spherical 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-(i) crystal facets, (ii) sharp edges, and (iii) amorphous surfaces of small nanoparticles with radii <10 nm-are considered. The impact forces are compared with their macroscopic counterparts described by nonlinear contact forces based on Hertz contact mechanics. In our simulations, edge and amorphous surface contacts with weak surface energy reveal that the average impact forces are in excellent agreement with the Hertz contact force. On the other hand, facet collisions show a linearly increasing force with increasing compression. Our results suggest that the nearly spherical nanoparticles are likely to enable some nonlinear dynamic phenomena, such as breathers and solitary waves observed in granular materials, both originating from the nonlinear contact force.
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, F N ∝ δ n with n = 3/2 derived by Hertz ( 1881), where δ 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 ≈ 3/2, 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.
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