Water-in-oil emulsion separation within a milli-fluidic device

A milli-fluidic method capable of continuous passive separation of water-in-oil emulsions with an efficiency of ∼90% is described. Experiments used high oleic sunflower oil or mineral oil as the continuous phase and aqueous solutions of methylene blue, crystal violet, or dextran with methylene blue as the dispersed phase. To achieve continuous passive separation, a device with opposing channel walls of disparate hydrophobicity is used to stabilize cocurrent laminar flow of oil and water. The disparity in hydrophobicity of the channel walls is accomplished by defining one length of the channel with a hydrogel, in this case polyethylene glycol. Emulsion separation is facilitated by introducing the emulsion at the water/hydrogel interface. Advantages of performing separations at the milli-fluidic scale are presented.

Graphical abstractPassive separation of a water-in-oil emulsion occurs spontaneously upon introduction into a milli-fluidic device where co-laminar flow of water and oil is stabilized by a hydrogel defining one length of the channel. Separation is achieved on the millimeter scale with separation efficiencies of ∼90% for aqueous solutions dispersed in a continuous oil phase (scale bar 800 μm).Figure optionsDownload full-size imageDownload high-quality image (54 K)Download as PowerPoint slideResearch highlights► Milli-fluidic scale water-in-oil emulsion separation with ∼90% efficiency. ► Stable co-laminar flow of immiscible liquids over several cm of channel length. ► Hydrogel–water interface facilitates breaking water-in-oil emulsion.