Pairwise scattering and bound states of spherical microorganisms

Abstract

Accurately calculating pairwise collisions between swimming microorganisms typically requires the use of numerical simulations in which hydrodynamic interactions are fully resolved. Here, we utilize analytical expressions for forces and torques acting on two closely separated spherical squirmers to evaluate their scattering dynamics and bound states, by varying incoming angles, the squirmer parameter \ensuremath{\beta}, and gravitational field strengths. These results compare well with full numerical solutions obtained using boundary element methods, highlighting lubrication theory as a candidate for use in future mesoscale continuum models.