Coalescence of compound droplets with unequal‐sized inner cores

The coalescence of compound droplets with unequal‐sized inner cores are numerically investigated by using a three‐dimensional Shan–Chen multicomponent lattice Boltzmann method. Distinct stages of liquid bridge growth, shape relaxation, and breakup/re‐coalescence phenomenon are discussed in detail. Simulations demonstrate that the outer bridge follows inertial scaling (), while the inner bridge exhibits viscous‐dominated linear growth (). Shape relaxation analysis shows the outer layer achieves equilibrium rapidly through a two‐stage logarithmic decay, while the inner core displays a three‐stage relaxation due to confinement effects. The interesting breakup/re‐coalescence phenomenon is characterized by the pressure field and fluid flow around the droplets, and a theoretical criterion for breakup is derived, which is further validated by a phase diagram. This work advances the fundamental understanding of the coalescence of compound droplets, with implications for industrial applications such as droplet reactors, drug delivery, and droplet‐based microfluidics.