Water-in-oil-in-water (W/O/W) double emulsion, which is defined as an aqueous droplet surrounded by an oil shell, dispersed in another aqueous phase, is frequently utilized in microcarrier applications. However, these double emulsions are inherently unstable and the molecular transport across the oil shell is difficult to precisely control. Herein, we utilize droplet microfluidics to prepare double emulsion droplets with various emulsifier composition in the micron thick oil shell to systematically investigate their effect on molecular transport. On the basis of the assumption that the molecules are transported across the oil-water interface <i>via</i> spontaneous emulsification, we tune the emulsifier structure and concentration to control the reverse micelle formation that leads to alteration in the permeability of oil membrane. Moreover, as highly permeable double emulsions usually suffer from its low stability, we employ library of conventional monomeric surfactants as well as a silicone based polymeric surfactant to simultaneously achieve enhanced emulsion stability and controlled molecular transport. Interfacial rheology results confirm that these both types of surfactants co-exist at the interface and that the anchoring of the polymeric surfactants at the interface ensures retention of the interface structure even under high osmotic pressure gradient and at elevated temperatures. As the additionally included monomeric surfactant in the oil shell enables to control the permeability of membrane, we envision that this study will provide new perspective in the rational design of stable double emulsions with controllable transport properties.

Design of double emulsions with enhanced stability and controllable molecular transport

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