Adhesive loose packing limit of axisymmetric nonspherical particles.

Abstract

We report computer simulations on the adhesive loose packing (ALP) limit of monodisperse axisymmetric ellipsoids, spherocylinders, and polymers by the random ballistic deposition method with the hit-stick-freeze assumption. The mean-field results demonstrate that the global packing fraction reaches a maximum value of 0.1469 for spheres, and it is nicely correlated with the aspect ratio in the 1 and -2 power-law relations for extremely oblate and prolate particles, respectively. For a given aspect ratio λ, the density follows the sequence of decreasing packing fraction: spheres > prolate ellipsoids > spherocylinders > polymers for λ<3, or spheres > spherocylinders > prolate ellipsoids > polymers for λ≥3. In addition, we highlight that the local coordination number excellently follows the normal distribution with a universal mean value of 2.001, regardless of the particle type and aspect ratio. The standard deviation is 0.730 for spheres, which increasingly approaches the asymptotic values of 0.850 for λ→0 and 1.112 for λ→+∞. Furthermore, we find that the radial distribution function is dominantly governed by the first contact shell with three distinct features, corresponding to the local minor-to-minor, minor-to-major, and major-to-major contacts between two particles. Finally, we present the universal correlation forms for both the global packing fraction and the standard deviation of coordination number, covering the wide aspect ratio range of 0.003-60 for ellipsoids and 1-60 for spherocylinders and polymers. We emphasize that the ALP limit represents the minimum-density state achievable via random ballistic deposition of strongly adhesive particles, while looser structures may be obtained by other cluster aggregation processes.