Droplet emulsification in microfluidic devices involves the constant formation of fresh interfaces between two immiscible fluids. When the multiphase system contains surfactant, dynamic mass transfer of the surfactant onto the interface results in a dynamic interfacial tension different from the static interfacial tension measured in an equilibrium state. In this work, we have systematically investigated the effects of surfactant concentration and type on the dynamic interfacial tension of two different liquid-liquid two phase systems [N-hexane/water-sodium dodecyl sulfate (SDS) and N-hexane/water-cetyltrimethylammonium bromide (CTAB)] rapidly producing relatively small droplets in coaxial microfluidic devices. Dynamic interfacial tension experiments using the pendent drop method and a tensiometer were conducted, and a semiempirical equation was developed to put into context the effects of surfactants and the experimental conditions on droplet formation and dynamic interfacial tension in dynamic microchannel flows. The results presented in this work provide a more in-depth understanding of the dynamic effects of surfactants on droplet formation and the precise controllable preparation of monodispersed droplets in microfluidic devices.
This work describes a novel microfluidic method to prepare monodispersed chitosan microspheres by using the solvent extraction method. Our strategy is that a chitosan/acetic acid aqueous solution is emulsified in an organic phase containing the extractant by using the co-flowing shear method in a co-axial microfluidic device. The formed droplets are in situ solidified within a synthesizing channel by the extraction of acetic acid from the chitosan aqueous droplets to the organic solution. Based on this approach, the size of chitosan microspheres can be successfully controlled from 100 mum to 700 mum in diameter with a variation of less than 4%. Furthermore, high loading efficiency (>95%) of Bovine serum albumin (BSA) can be in situ encapsulated. The present method has the advantages of actively controlling the droplet diameter, narrow size distribution, good sphericity, and having a simple and low cost process, with a high throughput. This approach for the preparation of chitosan microspheres will provide many potential applications for pharmaceutical area.
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