Mechanisms and control of single-step microfluidic generation of multi-core double emulsion droplets

Seyed Ali Nabavi,Goran T Vladisavljević,Vasilije Manović

doi:10.1016/j.cej.2017.04.008

Seyed Ali Nabavi, Goran T Vladisavljević + Show 1 more

Open Access

https://doi.org/10.1016/j.cej.2017.04.008

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Abstract

Single-step generation of monodisperse multi-core double emulsion drops in three-phase glass capillary microfluidic device was investigated using a micro-particle image velocimetry (micro-PIV) system. Phase diagrams were developed to predict the number of encapsulated inner drops as a function of the capillary numbers of inner, middle and outer fluid. The maximum stable number of inner drops cores in uniform double emulsion drops was six. Starting from core/shell drops, the formation of double emulsion drops with multiple cores was achieved by decreasing the capillary number of the outer fluid and increasing the capillary number of the middle fluid. A stable continuous jet of the middle fluid loaded with inner drops was formed at high capillary numbers of the middle fluid. Empirical correlations predicting the size and generation frequency of inner drops as a function of the capillary numbers and the device geometry were developed. Dual-core double emulsion drops were used as templates for the fabrication of polymeric capsules using “on-the-fly” photopolymerisation. The capsule morphology was controlled by manipulating the stability of the inner drops through adjusting the concentration of the lipophilic surfactant in the middle fluid. At low concentration of the lipophilic surfactant, inner drops coalesced during curing and single compartment capsules with thin shells were produced from dual-core drops. The core/shell capsules produced from multi-core drops were monodispersed and larger than those produced from core/shell drops in the same device.

Highlights

Multi-core double emulsions are complex emulsions composed of several inner drops dispersed in an immiscible middle phase, which is itself dispersed in the outer phase
Phase diagrams have been constructed based on the capillary numbers of the inner, middle and outer fluid to map out the regions where monodispersed double emulsion drops with specified number of inner drops can be generated
The formation of outer drops with multiple inner drops was achieved by decreasing the capillary number of the outer phase and increasing the capillary number of the middle phase

Summary

Introduction

Multi-core double emulsions are complex emulsions composed of several inner drops dispersed in an immiscible middle phase, which is itself dispersed in the outer phase. Multiple emulsions are produced in two consecutive emulsification steps through high-shear mixing of immiscible liquids [7] This approach is associated with broad particle size distribution, low batch-to-batch reproducibility, low encapsulation efficiency, high energy consumption, and a lack of control over the size of the drops and the number of encapsulated inner drops [8,9]. Using a two-step microfluidic device composed of three coaxial glass capillaries, Kim et al [11] observed that the number of inner drops increased with increasing middle-to-inner volumetric flow rate ratio. The number of inner drops was reduced by increasing the outer phase flow rate

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