Hydrodynamic Characteristics of Double Emulsions with a Viscoelastic Polymer Shell in Confined Microchannels

Microfluidic manipulation of double emulsions facilitates pharmaceutical encapsulation and material fabrication. This study investigates the hydrodynamic behavior of double emulsion droplets with viscoelastic polymer shells in confined microchannels through direct numerical simulations using the Volume of Fluid method. The polymer viscoelasticity is modeled by the exponential Phan-Thien-Tanner constitutive equation. A systematic analysis evaluates the effects of polymer viscoelasticity and flow conditions on flow field structure, stress distribution, droplet deformation, and migration velocity. Results show that higher viscosity suppresses radial velocity gradients and reduces vorticity intensity. In contrast, increased elasticity amplifies elastic stresses, leading to irregular velocity profiles and expanded high-vorticity regions. Narrower channels and higher continuous phase velocities enhance axial stretching and radial compression. Droplet velocity decreases with higher viscosity and larger diameter ratios but increases with relaxation time. Finally, a predictive model for average droplet velocity is developed, offering insights for optimizing viscoelastic double emulsion systems in microchannels.