Active control for droplet-based microfluidics

Active control of microdroplets in microchannels is an important task in droplet-based microfluidics. The break-up process of droplets at an T-junction is usually controlled passively by the fluidic resistance of the branches. We used thermal control to actively manipulate aqueous droplets in microchannels. The temperature affects both viscosity and interfacial tension between the phases. The concept was first simulated with a two-dimensional model. The simulation results show that increasing temperature at a branch can change the size ratio of the two daughter droplets from 0 to 1. That means, droplet switching is possible with this concept. Control of droplet size during the formation process and splitting process was demonstrated experimentally by varying the temperature of the branches. At a critical temperature, droplet switching can be achieved. The used control temperature of less than 40 °C shows that this active control concept is suitable for biochemical applications. Thermal control promises to be a simple and effective manipulation method for droplet-based lab on a chip.