Formation of core–shell droplets for the encapsulation of liquid contents

Accurate control of monodisperse core–shell droplets generated in a microfluidic device has a broad range of applications in research and industry. This paper reports the experimental investigation of flow-focusing microfluidic devices capable of producing size-tuneable and monodisperse core–shell droplets. The dimension of the core–shell droplets was controlled passively by the channel geometry and the flow rate of the liquid phases. The results indicate that microchannel geometry is more significant than flow rates. The highly controllable core–shell droplets could be subsequently employed as a template for generating core–shell microparticles with liquid core. Optical, electron scanning microscopy and X-ray computed microtomography showed that the geometry of the core–shell droplets remains unchanged after solidification, drying and collection. The present study also looks at the thermal stability of core–shell particles depending on the particle size. The larger core–shell particles with a thicker shell provide a higher resistance to heating at elevated temperature. The high degree of control with a flow-focusing microfluidic device makes this a promising approach for the encapsulation, storage, and delivery of lipophilic contents.