Effect of particle shape on the random packing density of amorphous solids

The packing density of a particulate solid strongly depends on the shape of the particles that are jammed at random close packing (RCP). To investigate the effect of particle shape on the RCP density of an amorphous solid, we studied jammed packings of binary mixtures of a-thermal or granular spherocylinders by means of mechanical contraction computer simulations. We showed that the packing density of a jammed solid can be optimized by using slightly elongated particles. Starting from the Bernal random sphere packing, the RCP density first raises to a maximum for nearly spherical rod-like particles and only beyond this maximum it monotonically decreases with the particle aspect ratio. We demonstrated that the density maximum appears not only for monodisperse systems but it is a universal feature of mixtures of randomly packed nonspherical particles. The position of the density maximum is also universal – the optimal packing is found when one of the components in the binary mixture has the unique particle aspect ratio 0.5, irrespectively of the mixture composition. In the limit of large particle size disparity in a bidisperse jammed system, we revealed a universal scaling for the total packing density as a function of the aspect ratio of one component, regardless of the shape of the second component. An amorphous solid composed of a binary mixture of spherical and non-spherical, slightly elongated particles.