Abstract
Breakup of droplets at bi-layer bifurcating junction in polydimethylsiloxane (PDMS) microchannel has been investigated by experiments and numerical simulation. The pressure drop in bi-layer bifurcating channel was investigated and compared with single-layer bifurcating channel. Daughter droplet size variation generated in bi-layer bifurcating microchannel was analyzed. The correlation was proposed to predict the transition between breakup and non-breakup conditions of droplets in bi-layer bifurcating channel using a phase diagram. In the non-breakup regime, droplets exiting port can be switched via tuning flow resistance by controlling radius of curvature, and or channel height ratio. Compared with single-layer bifurcating junction, 3-D cutting in diagonal direction from bi-layer bifurcating junction induces asymmetric fission to form daughter droplets with distinct sizes while each size has good monodispersity. Lower pressure drop is required in the new microsystem. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation, fission and sorting. The model system can be developed to investigate the encapsulation and release kinetics of emulsion templated particles such as drug encapsulated microcapsules as they flow through complex porous media structures, such as blood capillaries or the porous tissue structures, which feature with bifurcating junctions.
Highlights
Emulsions are ubiquitous in the daily life and have been extensively applied in food industry, cosmetics, pharmacy, and biochemical reactions [1,2,3]
A numerical study demonstrates that compared with single-layer bifurcating junction, 3-D cutting in diagonal direction from bi-layer bifurcating junction leads to droplet fission in more effectively way, obviating the need of expensive fabrication approach to ensure the microchannel has exquisitely controlled surface roughness and extremely sharp tip of bifurcating junction
The bifurcating junction arranged in two separate layers leads to asymmetric splitting of mother droplets, leading to formation of daughter droplets with distinct sizes [34], the mechanism for forming daughter droplets with different sizes has not been clearly elucidated, and the effect to daughter droplet size variations due to Capillary number has not been investigated quantitatively by experiments. These examples attest to the need for a comprehensive understanding of the role of pressure drop and Capillary number associated with the droplet breakup dynamics in bi-layer bifurcating microchannel
Summary
Emulsions are ubiquitous in the daily life and have been extensively applied in food industry, cosmetics, pharmacy, and biochemical reactions [1,2,3]. A numerical study demonstrates that compared with single-layer bifurcating junction, 3-D cutting in diagonal direction from bi-layer bifurcating junction leads to droplet fission in more effectively way, obviating the need of expensive fabrication approach to ensure the microchannel has exquisitely controlled surface roughness and extremely sharp tip of bifurcating junction. Pressure drop is the driving force of fluid flow in bifurcating microchannel for the formation and fission of droplets. These examples attest to the need for a comprehensive understanding of the role of pressure drop and Capillary number associated with the droplet breakup dynamics in bi-layer bifurcating microchannel. Daughter droplet size variation was confirmed from experimental study of bi-layer bifurcating microchannel, hypothesis was made to relate the size variation with the different pressure distribution in upper and lower channels, and the hypothesis was verified. The novel droplet fission approach provides insights for the design and fabrication of higher order emulsions with custom-made volume and shape, inspiring new biomedical and industrial applications based on microfluidic emulsification platform
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