OPTICALLY CONTROLLED MIXING IN MICRODROPLETS

Liquid microdroplets represent a convenient sys-tem for studies of mixing by chaotic advection in discrete microscopic volumes. The mixing proper-ties of the flows in microdroplets are governed by their symmetries, which give rise to invariant sur-faces serving as barriers to transport. Complete three-dimensional mixing by chaotic advection re-quires destruction of all flow invariants. To illustrate this idea, we demonstrate that complete mixing can be obtained in a time-dependent flow produced by motion of a microdroplet along a two-dimensional path. The theoretical predictions are confirmed by experiments that optically manipulate and mix mi-crodroplets