Performance of different microfluidic devices in continuous liquid-liquid separation

Droplet-based microfluidics exhibit numerous benefits leading to relevant innovations and many applications in various fields. The precise handling of droplets in capillaries, including droplet formation, manipulation, and separation, is essential for successful operation. Only a few reports are known concerning the separation of segmented flows, particularly the continuous separation of droplets, which is of high interest regarding the control of biochemical and chemical reactions or other applications where the contact time of the involved phases is crucial. Here, the separation must be flexible and adjusted to different flow parameters, such as the surface tension, the volumetric flow rates, and their ratios. This contribution presents two novel open-source approaches based on additive manufacturing and mechanical deforming for continuous liquid–liquid separation under various flow conditions. The Laplace pressure is the driving force for the separation, which is adjusted to the flow conditions by adapting the distance of pinning points provided by the design of the devices. Details of the device design and experimental setup are shown along with limitations to promote further development and to increase availability for researchers. With the right parameters, sophisticated separations can be realized by inexpensive laboratory equipment and simple control of them. It was found that the distance between the pinning points needs to enlarged for increasing volumetric flow rates and reduced for higher viscosities of the continuous phase respectively higher amounts of the dispersed phase. The open source approach of this article expands the exploration space in addition to commercially available phase separators only available to a selected group of people.

Graphical Abstract