Interfacial properties required for net propulsion of a capsule encapsulating squirmer(s)

A viscous drop enclosing a swimmer is known to propel due to the flow created by the swimmer inside. However, it takes a lot more for a giant unilamellar vesicle to move by encapsulating a motile swimmer. In this work we investigate the role of interfacial rheology in the propulsion of a capsule encapsulating a squirmer. This capsule can be a viscous drop or a vesicle, and we focus on the interaction between the capsule interface and the squirmer to elucidate the conditions for propulsion of the capsule+squirmer complex. In addition to shear viscosity and dilatational viscosity, we also incorporate a weak extensibility and permeability to explore various combinations of surface properties that could work with the internal squirmer to produce net propulsion for the whole capsule. This is joint work with Bryan Quaife, On Shun Pak and Herve Nganguia.