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Göttingen, Germany

Baret J.-C.,Droplets
Lab on a Chip - Miniaturisation for Chemistry and Biology

Surfactants are an essential part of the droplet-based microfluidic technology. They are involved in the stabilization of droplet interfaces, in the biocompatibility of the system and in the process of molecular exchange between droplets. The recent progress in the applications of droplet-based microfluidics has been made possible by the development of new molecules and their characterizations. In this review, the role of the surfactant in droplet-based microfluidics is discussed with an emphasis on the new molecules developed specifically to overcome the limitations of 'standard' surfactants. Emulsion properties and interfacial rheology of surfactant-laden layers strongly determine the overall capabilities of the technology. Dynamic properties of droplets, interfaces and emulsions are therefore very important to be characterized, understood and controlled. In this respect, microfluidic systems themselves appear to be very powerful tools for the study of surfactant dynamics at the time- and length-scale relevant to the corresponding microfluidic applications. More generally, microfluidic systems are becoming a new type of experimental platform for the study of the dynamics of interfaces in complex systems. © 2012 The Royal Society of Chemistry. Source

Lim J.,Droplets | Lim J.,Max Planck Institute for Biophysical Chemistry | Maes F.,Droplets | Taly V.,Paris-Sorbonne University | And 2 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology

We demonstrate a new concept for reconfigurable microfluidic devices from elementary functional units. Our approach suppresses the need for patterning, soft molding and bonding when details on a chip have to be modified. Our system has two parts, a base-platform used as a scaffold and functional modules which are combined by 'plug-and-play'. To demonstrate that our system sustains typical pressures in microfluidic experiments, we produce droplets of different sizes using T-junction modules with three different designs assembled successively on a 3 × 3 modular scaffold. © 2014 the Partner Organisations. Source

Lim J.,Droplets | Caen O.,Droplets | Caen O.,Paris-Sorbonne University | Vrignon J.,Droplets | And 5 more authors.
18th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2014

Several systems have been proposed for the high-throughput production of monodisperse emulsions by parallelizing droplet makers. Such systems have two main limitations: they allow the use of only one disperse phase and are based on multiple layer microfabrication techniques. We present a solution offering the possibility of manipulating simultaneously 10 different disperse phases on a layer device. This system allows the high throughput production of highly monodisperse emulsions with user-defined chemical composition. We demonstrate the reliability of our system by measuring the kinetics of β-galactosidase in droplets using 9 different concentrations of a fluorogenic substrate and 1 internal reference. © 14CBMS. Source

Tan S.H.,Droplets | Semin B.,Droplets | Baret J.-C.,Droplets
Lab on a Chip - Miniaturisation for Chemistry and Biology

We demonstrate the control of droplet sizes by an ac voltage applied across microelectrodes patterned around a flow-focusing junction. The electrodes do not come in contact with the fluids to avoid electrochemical effects. We found several regimes of droplet production in electric fields, controlled by the connection of the chip, the conductivity of the dispersed phase and the frequency of the applied field. A simple electrical modelling of the chip reveals that the effective voltage at the tip of the liquid to be dispersed controls the production mechanism. At low voltages (≲ 600 V), droplets are produced in dripping regime; the droplet size is a function of the ac electric field. The introduction of an effective capillary number that takes into account the Maxwell stress can explain the dependance of droplet size with the applied voltage. At higher voltages (≳ 600 V), jets are observed. The stability of droplet production is a function of the fluid conductivity and applied field frequency reported in a set of flow diagrams. © 2014 The Royal Society of Chemistry. Source

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