Spontaneous Oscillations and Synchronization of Active Droplets on a Water Surface via Marangoni Convection

Shape-oscillations
and synchronization are intriguing phenomena
in many biological and physical systems. Here, we report the rhythmic
mechanical oscillations and synchronization of aniline oil droplets
on a water phase, which is induced by Marangoni convection during
transfer of the solute. The repetitive increase and decrease in the
surface concentration in the vicinity of the contact line leads to
the oscillations of droplets through an imbalance in surface tensions.
The nature of the oscillations depends on the diameter of the droplet,
the depth of the bulk aqueous phase, and the concentration of the
aqueous phase. A numerical simulation reproduces the essential behaviors
of active oscillations of a droplet. Droplets sense each other through
a surface tension gradient and advection, and hydrodynamic coupling
in the bulk solution induces the synchronization of droplet oscillations.