  The issue of the buckling mechanism in droplets stabilized by solid particles
(armored droplets) is tackled at a mesoscopic level using dissipative particle
dynamics simulations. We consider spherical water droplet in a decane solvent
coated with nanoparticle monolayers of two different types: Janus and
homogeneous. The chosen particles yield comparable initial three-phase contact
angles, chosen to maximize the adsorption energy at the interface. We study the
interplay between the evolution of droplet shape, layering of the particles,
and their distribution at the interface when the volume of the droplets is
reduced. We show that Janus particles affect strongly the shape of the droplet
with the formation of a crater-like depression. This evolution is actively
controlled by a close-packed particle monolayer at the curved interface. On the
contrary, homogeneous particles follow passively the volume reduction of the
droplet, whose shape does not deviate too much from spherical, even when a
nanoparticle monolayer/bilayer transition is detected at the interface. We
discuss how these buckled armored droplets might be of relevance in various
applications including potential drug delivery systems and biomimetic design of
functional surfaces.
