Study on the interfacial dynamics of free oscillatory deformation and breakup of single-core compound droplet

Abstract

Compound droplets are usually taken as microcontainers for biomedical and material encapsulation applications in which a good understanding of the free oscillatory deformation and breakup behavior is essential. In this work, the dynamics of free oscillatory deformation and breakup of a single-core compound droplet with an initial ellipsoidal shell was investigated numerically using the volume-of-fluid method. The effects of droplet diameter and the outer droplet initial deformation parameter are considered. Four outcomes are identified: oscillatory deformation, separation, separation breakup, and breakup. The evolution of the kinetic energy and pressure field of the compound droplet for the four typical outcomes is also analyzed in detail. A clear boundary exists between the first and the latter three outcomes (initial deformation parameters of 0.600–0.773), while the critical factor for the latter three outcomes is the inner and outer droplet diameter ratio. The oscillatory deformation is characterized by the inner and outer droplet undergoing a finite deformation and subsequent oscillatory behavior, with the maximum deformation of the inner and outer droplets being related to the energy transfer between the two, and the outer droplet being a periodic decaying oscillation, while the inner droplet is a large deformation oscillation interspersed with a small deformation oscillation. Separation, separation breakup, and breakup are characterized by breakup at the inner or outer interface during deformation; separation and breakup times are largely dependent on droplet diameter and the initial deformation parameter of the outer droplet; and the neck width at separation is also analyzed in detail.