Liquid bridge instability applied to microfluidics
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This paper presents a new way of combining and mixing reagents within one droplet, which may then be used as a microfluidic biochemical reactor. This is made possible by coalescing aqueous droplets on opposing microcapillary tips immersed in density-matched silicone oil. It was found that there are two possible outcomes from a binary capillary-suspended droplet interaction. The droplets may coalesce to form a stable fluid bridge between opposing capillary tips. The droplets may, however, coalesce to form an unstable liquid bridge that quickly ruptures resulting in the two fluid volumes combining into one droplet suspended from a single capillary tip. The stability boundary that determines one outcome or the other was found to be related to a number of variables that describe the equilibrium shape of the liquid bridge interface. Suspending the host droplet from a larger diameter microcapillary dramatically increases the range of volumes that the system can combine by shifting the stability boundary. This ensures the desired effect of pinch-off near the tip of the finer microcapillary thereby dispensing microfluidic samples in one direction.
KeywordsLiquid bridges Droplet coalescence Interfacial tension Microfluidic mixing
Polymerase chain reaction
The authors would like to thank Stokes Research Institute, University of Limerick and le Laboratoire de Génie Mécanique de Toulouse for the financial support and facilities, which made this research possible. The authors would also like to extend their gratitude to Dr. Laurent Prat and Flavie Sarrazin from Laboratoire de Génie Chimique, Toulouse for the use of the Fermat Platform high-speed camera. We would also like to thank Prof. Catherine Colin, Institut de Mécanique des Fluides de Toulouse for enlightening discussions on the subject.
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