(61d) Effects of Particle Shape and Surface Roughness on Van Der Waals Interactions

The van der Waals interaction for particles is one of the critical components to understanding particle aggregation and assembly. Although anisotropic particle shapes and surface roughness are known to unavoidable in nanocrystalline materials, their impacts have not been intensively investigated. We develop a scheme to determine the van der Waals forces and torques between cubic particles as a simple case. Our study with representative configurations and relative orientations shows that the van der Waals torque due to anisotropic particle shapes is appreciable at nearly all configurations and mutual angles, dominating over Brownian torque for various materials systems and conditions. Surface roughness enhances the particle shape effect, resulting in stronger van der Waals interactions ascribed to protrusions on the surfaces. We will discuss the importance of both effects on dynamics of two approaching particles. Our results demonstrate that both effects play crucial role in the energetics and kinetics of various particle-scale and emergent phenomena, such as crystal growth by oriented attachment, nanomaterials synthesis/assembly, and mud flow rheology.