Numerical simulation on free oscillation interfacial dynamics of single-core compound droplet driven by shell deformation

Abstract

Compound droplets are often used as microcontainers in biomedical, material encapsulation, and so on, and a good understanding of their free oscillatory behavior is essential for controllable product preparation. Herein, the free oscillatory deformation behavior of single-core compound droplet induced by shell deformation is studied computationally using the volume-of-fluid (VOF) method. The effects of the inner droplet diameter, the outer droplet initial deformation and physical properties are considered. The results show that outer droplet oscillation has obvious periodicity and damping attenuation mechanism, and the inner droplet has two oscillation forms: large-deformation forced oscillation and small-deformation free oscillation. The oscillation period is positively correlated with the inertial force, while the damped attenuation mechanism is dominated by the viscous force, and the presence of the inner droplet and the increase of its diameter will enhance the inertial and viscous forces of the outer droplet. The deformation degree of the inner and outer droplet is related to the energy transfer between the two and the initial interfacial energy, which is generally greater for the outer droplet than for the inner droplet, but the larger diameter ratio makes the opposite situation, and the critical value lies between the diameter ratio of 0.625–0.75. The obtained results will provide the possibility to control the morphological structure of the compound droplets after preparation.