Rebound of a Particle from a Solid Surface with a Viscous or Nonlinear Viscoelastic Liquid Film in the Contact Zone
A summary is presented of previous work on the cohesive characteristics of thin films of viscous and nonlinear viscoelastic liquids that were studied using atomic force microscopy (AFM) for a range of separation velocities. It was possible to estimate the measured maximum cohesive forces as a function of the Capillary number by using models of the capillary and viscous forces, and also by developing a closed-form approximation for the nonlinear viscoelastic forces. Polymeric liquid binders are used in wet granulation and when the concentration and molecular weight exceed critical values, such binders are viscoelastic. In the current work, the models employed in the AFM studies were applied to the impact of particles on a planar half-space with viscous and viscoelastic liquid films in the contact region. This involved a simplistic description of an impact in which the elastic deformation of the particles was ignored. Nevertheless, it was demonstrated that, under conditions leading to stick for a viscous fluid, it is likely that a viscoelastic fluid will rebound. The molecular mechanisms involved are discussed in the paper.