Encapsulation with an interfacial liquid layer: Robust and efficient liquid-liquid wrapping.

Hypothesis: We developed an impact driven liquid-based encapsulation method by utilizing the fundamental thermodynamic tendency of a suitable three-liquid combination towards formation of a core-shell structure.

Experiments: Stable wrapping is achieved by impinging a core drop from a vertical separation on an interfacial liquid film floating on a host liquid bath. The resulting interfacial dynamics is captured using a high-speed camera. Several combinations of impact height and interfacial film thickness are investigated for a quantitative description of the phenomena.

Findings: The stability and integrity of the liquid encapsulating layer are confirmed both experimentally (by analyzing the under-liquid wetting signature) and theoretically (by equilibrium thermodynamic analysis). Effect of viscous dissipation on the dynamics is explained and a consequent theoretical threshold for minimum allowable drop size is provided. A non-dimensional experimental regime is also constructed for successful encapsulation in terms of impact kinetic energy and interfacial layer thickness. Additionally, the encapsulating layer is shown to protect the core drop even when the core and host liquids are miscible. The demonstrated method is simple to implement yet robust, offers flexibility regarding varying both the size and the material properties of the core and shell liquids and consistently produces stable monodispersed encapsulated drops in an ultrafast manner.