Thermally mediated control of liquid microdroplets at a bifurcation

The ability to precisely control the motion of droplets is essential in droplet-based microfluidics. It serves as the basis for various droplet-based devices. This paper presents a thermal control technique for microdroplets at a bifurcation. Control was achieved using an integrated microheater that simultaneously induces a reduction in fluidic resistance and thermocapillarity. The temperature of the heater was monitored by an integrated temperature sensor. At a bifurcation with symmetric branches, a droplet can be split into two daughter droplets of controllable sizes or entirely switched into a desired branch. The physics of this phenomenon was investigated with the help of a numerical model. Splitting and switching were demonstrated within an operational temperature range 25-38 °C. The relatively low operational temperature range allows this technique to be used for droplets containing biological samples. The present control concept is not limited to bifurcations, but can be employed in other geometries.