Manipulation and control of droplets on surfaces in a homogeneous electric field

Control of droplet coalescence is a major challenge of droplet microfluidics. Here, the authors show that homogenous external electric field can induce dipoles inside droplets, which can be used to withdraw samples from an array of droplets. A method to manipulate and control droplets on a surface is presented. The method is based on inducing electric dipoles inside the droplets using a homogeneous external electric field. It is shown that the repulsive dipole force efficiently suppresses the coalescence of droplets moving on a liquid-infused surface (LIS). Using a combination of experiments, numerical computations and semi-analytical models, the dependence of the repulsion force on the droplet volumes, the distance between the droplets and the electric field strength is revealed. The method allows to suppress coalescence in complex multi-droplet flows and is real-time adaptive. When the electric field strength exceeds a critical value, tip streaming from the droplets sets in. Based on that, it becomes possible to withdraw minute samples from an array of droplets in a parallel process.

Automated summary

The authors demonstrate a method for controlling droplet coalescence by inducing dipoles inside droplets using an external electric field. The repulsive dipole force efficiently suppresses droplet coalescence on a liquid-infused surface, allowing for the manipulation and control of droplets. These findings reveal the dependence of the repulsion force on droplet volumes, distance between droplets, and electric field strength.