An investigation of the hydrodynamic resistance of droplets in microchannels using active control

Droplet microfluidics involves two immiscible phases: typically, water in oil. The passive manipulations of the droplets highly depend on the hydrodynamic resistance of the channel network. Both phases contribute to the overall resistance. However, while the continuous phase (i.e. oil) can be calculated accurately from the literature, the contribution to the resistance from the droplet(s) is a complex relationship that has yet to be fully quantified. Variables contributing to droplet hydrodynamic resistance include: viscosity ratio, droplet speed, surface tension, channel geometry, size and spacing of droplets.

The objective of this empirical study is to estimate the resistance of a channel containing a droplet under various conditions. Although this problem has been approached by several researchers, the methods herein proposed is novel as it leverages a visual-feedback assisted active control platform rather than a passive method. This platform allows the generation of a single droplet under various conditions. From the input (pressure) and the output (water-oil interface displacement) with respect to time, the properties of the system can be retrieved using system identification techniques. Hence, an empirical correlation for predicting droplet resistance can be obtained.