Vibration‐assisted droplet formation of shear‐thinning polymeric fluids in microchannels: Mechanism and scaling laws

Abstract Achieving monodisperse droplets from high‐viscosity, shear‐thinning polymeric fluids presents a fundamental hydrodynamic challenge, as viscous damping and non‐Newtonian rheology modify the growth of capillary‐driven breakup instabilities. This work reports a vibration‐assisted active control strategy to regulate the droplet formation process. Three‐dimensional direct numerical simulations reveal that vibration induces vortices near the necking region, enhancing shear rates and reducing apparent viscosity to ensure rupture. A stability‐based interpretation indicates that the optimal frequency aligns with the maximum growth rate of the instability. A unified flow regime map based on compound dimensionless groups is established to predict the boundary between the uniform droplet and random droplet regimes. Furthermore, a dimensionless scaling law is developed to characterize droplet size. Compared to non‐vibrated conditions, the active vibration reduces the coefficient of variation of microspheres by a factor of up to 7.8. This study provides a methodology for the fabrication of uniform polymeric droplets and microparticles.