The coagulation and re-separation process of particles in a slow viscous flow*

The coagulation and re-separation process of two spherical particles immersed in a low-Reynolds-number flow is investigated analytically. The hydrodynamic interaction has to be considered in the present case since such an interaction between the two touching particles turns significant. The complete solution to the exterior velocity field around the two particles can be constructed using the extended successive reflection method, and the forces and couples acting on the two particles are then expressed as a set of dynamical equations of motion. These equations are adopted to describe the motion of the two particles by numerically integrating the equations with respect to time. Our results show that the reversibility of the Stokes equations is broken due to the contact friction between the particle surfaces if the particles touch each other ever before.