Rich collision dynamics of soft and sticky crystalline nanoparticles: Numerical experiments

Abstract

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.

Small nanoparticles, surface geometry and contact forces

“…This hysteresis observed in the force-overlap curves, which is also typical in colliding viscoelastic bodies, indicates the loss of translational kinetic energy of the nanoparticles during collision. The existence of energy dissipation corroborates earlier findings: the coefficient of restitution of colliding nanoparticles is less than 1 if the impact velocity is sufficiently high [12,[16][17][18]20,27]. At an impact velocity as low as the thermal velocity, the coefficient of restitution may exceed 1 [12,16,17,31,32].…”

“…If the impact velocity is set low enough, the attractive force would no longer be negligible as the compressional elastic force decreases. At a velocity below a threshold, determined by the Weber number, nanoparticles actually stick together [6,16,20,27]. In the velocity range and the weak adhesion considered, nanoparticles do not adhere together.…”

“…To this end, a modified LJ potential described in equation (2.1) is introduced, which contains a parameter c αβ in the second term, where α, β ∈ {ξ , η}. This parameter allows us to vary the attraction between atoms, as used in [16,19,20,27]. A situation where c αβ = 1 recovers the standard LJ potential,…”

“…This type of plastic deformation is not observed in the crystalline nanoparticles at the same velocity. At the transition between the elastic and plastic deformations, crystalline nanoparticles begin to crack and dislocations generated on the contact area propagate through the nanoparticles [18,27,45,46]. On the other hand, the underlying mechanism of plastic deformation in amorphous solids, such as metallic glasses, is generally shear band formation instead of dislocation.…”

Bouncing window for colliding nanoparticles: Role of dislocation generation

“…To this end, we study a Lennard-Jones (LJ) material. We note that this (computationally) important system has already been used repeatedly in previous work for studying NP collisions [9][10][11][12][13][14][15][16]. However, some of these simulations have been performed at higher collision energies (leading to NP fragmentation), or with strongly modified potentials, which strongly alter the collision dynamics.…”