Mobilities of a drop and an encapsulated squirmer

Abstract

We have analyzed the dynamics of a spherical, uni-axial squirmer which is located inside a spherical liquid drop at general position rs. The squirmer is subject to an external force and torque in addition to the slip velocity on its surface. We have derived exact analytical expressions for the linear and rotational velocity of the squirmer as well as the linear velocity of the drop for general, non-axisymmetric configurations. The mobilities of both, squirmer and drop, are in general anisotropic, depending on the orientation of rs, relative to squirmer axis, external force or torque. We discuss their dependence on the size of the squirmer, its distance from the center of the drop and the viscosities. Our results provide a first step towards a discussion of the trajectories of the composite system of drop and enclosed squirmer.