A simple model incorporating the effects of deformation and asperities into the van der Waals force for macroscopic spherical solid particles

The van der Waals interaction between perfectly spherical, infinitely hard spheres is well understood. Unfortunately, real powder particles are not in finitely hard and rarely spherical. Those particles that are approximately spherical are often covered in small asperities. It is often believed that the size of these asperities dominates the cohesive force between powder pa rticles, This paper rigorously examines this phenomenon and demonstrates th e regimes over which the asperities dominate the cohesive force and when th e particle size dominates. Deformation of particles is also investigated wi th a simple model and is shown to produce a significant increase in cohesiv e force. We demonstrate that previous simple models for calculating the eff ect of deformation are inadequate, as they ignore effects that can be as la rge as the correction they suggest. This can lead to an underestimation of the cohesive force by a factor of approximately 2. (C) 2000 Academic Press.