Separation of Janus droplets and oil droplets in microchannels by wall-induced dielectrophoresis

•The electrically induced Janus droplets (EIJDs) were fabricated by partially coating oil droplets with nanoparticles.•The wall-induced DEP lateral migrations of oil droplets and EIJDs were studied experimentally and theoretically.•The separations of oil droplets and EIJDs by wall-induced DEP were achieved.•The separation size is controllable by simply adjusting the applied voltages.

The continuous separation of different types of droplets from a mixture is important in industrial and research applications. Currently researches for droplet separation focus on homogeneous emulsion droplets, and there is no study on the separation of heterogeneous droplets. The wall-induced dielectrophoresis, which originates from the non-uniform electrical field around a sphere nearby a planar wall, can be applied to separate dielectric particle and cells. In this work, the continuous separations of oil droplets and the electrically induced Janus droplets (EIJDs) in a microchannel by using the wall-induced dielectrophoresis method were presented. The wall-induced dielectrophoretic lateral migration of a droplet depends on the size and surface charge of the droplet. In this study, the wall-induced dielectrophoretic lateral migrations of oil droplets and Janus droplets in a straight microchannel under different strengths of electrical fields were investigated first, and the experimental results match well with the theoretical predictions. Then, the separations of oil droplets by size, separations of Janus droplets by size, and separation of mixtures of Janus droplets and oil droplets with the same size were conducted, respectively. The experimental results demonstrate that, with this method, the separations of target oil droplets or Janus droplets with specific size can be accomplished by simply adjusting the voltages applied to the microchannel.