Chapter 7: Self-propelling Droplets

Self-propelled droplets provide a very simple and accessible realization of active colloids. To achieve spontaneous and self-sustained propulsion, they only require a generic chemical reaction or molecular transport at an emulsion interface that is susceptible to a chemohydrodynamic instability based on the advection of chemical species by self-induced interfacial flows. In contrast to most solid phoretic colloids, they do not require a pre-engineered front-back asymmetry to function. In this chapter we cover the foundational chemical and engineering aspects on how to produce simple and complex active emulsions, discuss the theoretical foundations of their modeling and the current experimental and numerical evidence of their complex dynamics, as well as their motility under a number of experimental parameters and boundary conditions.