Abstract
A simple and robust co-flowing microfluidic device for double emulsion preparation is designed and assembled to visually study the double emulsion formation by the use of a microscope and high-speed camera. Using a visualization system, the transient processes of double emulsion formation in co-flowing stream are observed and recorded for a variety of flow rates. The effects of flow rates of each fluid on flow modes, drop sizes, and polydispersities are examined and analyzed. The results indicate that the detaching of the inner drops accelerates the detaching of the outer drops and speeds up the drop formation process of double emulsions. The manipulation of flow rates is capable to actively control the sizes of the inner and outer drops as well as the number of inner drops encapsulated. Without surface modification, the microfluidic device produces a variety of emulsions, including the single-core and multi-core O/W/O double emulsions as well as binary emulsions of single and double emulsions. The proposed co-flowing microfluidic device is highly desirable in producing double emulsions in an easy and cheap way.
Highlights
Monodispersed drops in emulsions [1,2] are ideal vessels for reactions in small scale [3], control release [4] and drug delivery [5]
The results indicate that, multi-core double emulsions produced by the one-step device are polydispersed in both inner and outer drops and are only generated under the condition when the flow rate of the outer fluid is at the same magnitude with the middle and inner fluid
A cheap and robust co-flowing microfluidic device is proposed in this paper to generate double emulsions in one step without requirement of surface modification
Summary
Monodispersed drops in emulsions [1,2] are ideal vessels for reactions in small scale [3], control release [4] and drug delivery [5]. Additional scalability and flexibility was achieved by Wang et al [16] who developed a modular microfluidic device comprised of a drop maker, connector, and liquid extractor Using these modules, the multi-core, multi-component double emulsions and high-order emulsions in a variety of forms can be produced by controlling the flow rates. A three-dimensional co-flowing microfluidic device is designed and assembled in the current investigation with the outlets of the inner fluid and middle fluid on the same cross section where the double emulsions are formed in one step. Based on this microfluidic device, the hydrodynamic behaviors of various drop formation modes are examined via a visualization system using a microscope and high-speed camera. The influence of flow rates on flow modes, drop sizes, and polydispersities are examined and analyzed
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