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Description
We present the results of an ongoing experimental study about the statics and dynamics of 2D microfluidic crystals confined in a patterned microchannel. More precisely, droplets of uniform size are produced with a T-junction and inserted into a Hele-Shaw cell whose top is patterned with micrometric holes made by standard lithography techniques. A small hole etched in the top wall generates an attractive force that can be estimated from geometric arguments [1]. In the presence of external flow, the droplet pushed by the continuous phase can remain trapped only if the pinning strength of the hole is sufficient to balance the drag force. An anchored drop can remain stationary indefinitely as long as the driving flow rate remains below a critical value that depends on the sizes of the well and droplet. The statics and dynamics of pressure driven 2D droplet crystals in the patterned Hele-Shaw are recorded via a video camera and the time position of the crystal droplets is deduced by using machine learning visual methods.
[1] R Dangla, S Lee, CN Baroud, Trapping microfluidic drops in wells of surface energy, Phys. Rev. Lett. 107, 124501 (2011).