Abstract
This study presents the development of 3-dimensional PDMS microfluidic channel network that is capable of generating water-in-oil-in-water double emulsions in a controlled manner. Microfluidic channels are designed to guide the individual and coupled flows, which are driven by 3 independent sources, and to manipulate the flow fields along the emulsification process. In addition to liquid flow-rates and channel geometries, interfacial tensions are also critical to the emulsification process. By introducing surfactant molecules to the interfaces, the breakup process and the emulsion structure are stabilized as desired. In the prototype demonstration, plastic molds with millimeter and micrometer-sized channels were fabricated by milling and multi-step lithography processes, respectively. The molded PDMS plates were surface treated and bonded irreversibly to form stereo channel network. Afterward, the generation of water-in-oleic-acid-in-water double emulsions was performed by the fabricated PDMS devices with various flow-rate and surfactant combinations. It was verified in the trials that: (1) totally three different breakup modes can be successfully induced to generate double emulsions, and (2) the sizes and the core-to-shell ratios of the resulted emulsions can be controlled independently by the outermost and the inner flow-rates, respectively. As such, the presented double emulsification scheme could potentially realize the consistency and controllability on the emulsion structure and size distribution, which are desired for various biological and pharmaceutical applications.