Effects of the long-range cohesive forces in binary particle packing dynamics

Studies on random packing of bidispersive particles have shown that such systems can capture the underlying behavior of more complex phenomena found in physics and materials engineering. In industry, bidispersive particles are used to allow the increase of density and fluidity of the formed compounds. The understanding of the dynamics of these processes is therefore of great theoretical and practical interest. In this paper, we perform molecular dynamics (MD) simulations to study the packing process of particles with binary size distribution. Samples with different particle population densities (p) as well as different particle size ratios (λ) have been assessed. The initial positions of five thousand non-overlapping particles are assigned inside a confining rectangular box. After that, the system is allowed to settle under gravity towards the bottom of the box. Both the translational and rotational movements of each particle are considered in the simulations. In order to deal with interacting particles, we take into account both the contact and long-range cohesive forces. The normal viscoelastic force is calculated according to the nonlinear Hertz model, whereas the tangential force is calculated through an accurate nonlinear-spring model. Assuming a molecular approach, we account for the long-range cohesive forces using a Lennard-Jones(LJ)-like potential. The packing processes are studied assuming different long-range interaction strengths. We carry out statistical calculations of the different quantities studied including packing density, radial distribution function and orientation pair correlation function.