Close packing density and fracture strength of adsorbed polydisperse particle layers

Abstract

The close packing density of log-normal and bimodal distributed, surface-adsorbed particles or discs in 2D is studied by numerical simulation. For small spread in particle size, the system orders in a polycrystalline structure of hexagonal domains. The domain size and the packing density both decrease as the spread in particle size is increased up to 10.5 ± 0.5%. From this point onwards the system becomes amorphous, and the close packing density increases again with spread in particle size. We argue that the polycrystalline and amorphous regions are separated by a Kosterlitz–Thouless-type phase transition. In the amorphous region we find the close packing density to vary proportional to the logarithm of the friction factor, or cooling rate. We also studied the fracture behaviour of surface layers of sintered particles. Fracture strength increases with spread in particle size, but the brittleness of the layers shows a minimum at the polycrystalline–amorphous transition. We further show that mixing distributions of big and small particles generally leads to weaker and more brittle layers, even though the close packing density is higher than for either of the particle types. We point out applications to foam stability by the Pickering mechanism.