Computer simulation of the packing of nanoparticles

The packing of nanoparticles down to 20 nm is simulated by the discrete element method (DEM). The model is validated by good agreement between the simulated and measured porosity. It is found that the previous relationship between porosity and the force ratio of cohesion to gravity can also be applied to the packing of nanoparticles. However, different from microparticles, nanoparticle packing begins with agglomeration and then the agglomerates are packed together. The resulting packing structure is thus more like chains of agglomerates. The agglomeration process becomes more dominant when particle size decreases. Due to agglomeration, the packing structure of nanoparticles is found to be more sensitive to the initial porosity than that of microparticles, and the effects are analysed in terms of the temporal evolution of agglomerates. The fractal analysis indicates that the agglomerates are fractal-like while the whole packing is not fractal-like. The packing structure can be characterized by the radial distribution function and coordination number. The results indicate that for nanoparticles, with decreasing particle size, local packing structure becomes denser although the overall porosity increases, which is different from that of microparticles. The results link the packing of particles at different scales, from macro to nano, while also reveal the critical difference between the packing of nanoparticles and that of other particles.