Double-layered microcapsules, which usually consist of a core (polymeric) matrix surrounded by a (polymeric) shell, have been used in many industrial and scientific applications such as microencapsulation of drugs and living cells. Compound concentric nozzle-based jetting has been favored due to its efficiency and precise control of the core-shell compound structure. Thus far, little is known about the underlying formation mechanism of double-layered microcapsules in compound nozzle jetting. This study aims to understand the formability of double-layered microcapsules in compound nozzle jetting by coupling a theoretical analysis with numerical simulations. A linear temporal instability analysis is used to define the perturbation growth rate and its ratio as a function of the wavenumber; and a computational fluid dynamics (CFD) method is implemented to model the microcapsule formation process in order to determine the good microcapsule forming range based on the growth ratio curve. Using a pseudo-bisection method, the lower and upper bounds of the good formability range have been determined for a given materials-nozzle system. The proposed formability prediction methodology has been implemented and validated in modeling a water-poly (lactide-co-glycolide) (PLGA) – air compound jetting system with satisfactory prediction results.

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