Dynamic Simulation of Random Packing of Polydispersive Fine Particles

In this paper, we perform molecular dynamics (MD) simulations to study the two-dimensional packing process of both monosized and random size particles with radii ranging from $1.0 \, \mu m$ to $7.0 \, \mu m$. The system was allowed to settle under gravity towards the bottom of a $300 \, \mu m \times 500 \, \mu m$ rectangular box. The initial positions as well as the radii of five thousand fine particles were defined along the box by using a random number generator. Both the translational and the rotational movement of each particle were considered in the simulations. In order to deal with interacting fine particles, we take into account both the contact forces and the long-range dispersive forces. We account for normal and static/sliding tangential friction forces between particles and between particle and wall by means of a linear model approach, while the long-range dispersive forces are computed by using a Lennard-Jones like potential. The packing processes were studied assuming different long- range interaction strengths. We carry out statistical calculations of the different quantities studied such as packing density, mean coordination number and time derivative of the kinetic energy as the system evolves over time. A size spectral analysis was employed to obtain the radial distribution function (RDF) of the random close-packed structures (RCPS) for the case of random size particles. We find that the long-range dispersive forces can strongly influence the packing process dynamics as they might form large particle clusters, depending on the intensity of the long-range interaction strength. However, the general shape of the RDFs for the RCPS is seen to be more influenced by the hardness of the particles than by the long-range dispersive forces.