On the compound sessile drops: configuration boundaries and transitions

The geometry of compound sessile drops at equilibrium on a flat substrate can exhibit a variety of complicated morphological configurations. In this paper, we first investigate the configuration boundaries of the compound sessile drops in a wide parameter space, where a specific configuration is not stable outside its boundaries. Then, we focus on the transitions among the axisymmetric configurations, i.e. encapsulation, lens and collars. The configuration transitions result from the variation of the wettability of the substrate and the volume ratio of the two component droplets. With the help of theoretical analysis and numerical simulations, we obtain previously unidentified criteria for the onset of configuration transition, identify the irreversible and reversible configuration transitions, reveal the dynamic behaviours of configuration transitions that are not accessible to theoretical analysis, and provide a further step towards the ultimate purpose of such work, which is the controllable reconfiguration of the compound sessile drops.

Automated summary

The study investigates the configuration boundaries of compound sessile drops on a flat substrate and focuses on transitions among axisymmetric configurations like encapsulation, lens, and collars. These transitions are influenced by changes in substrate wettability and the volume ratio of different droplet components. The research identifies criteria for configuration transition onset, distinguishes between irreversible and reversible transitions, uncovers dynamic behaviors of transitions not accessible to theoretical analysis, and advances towards controllable reconfiguration of compound sessile drops.