Capillary‐Bridge Mediated Manipulation of Nonmagnetic Droplets Using Low Magnetic Fields with Self‐Locking Feature

Abstract

AbstractActive control of droplet motion on solid surfaces has attracted tremendous attention due to its wide range of applications. Manipulation of nonmagnetic droplets using magnetic fields is realized using magnetoresponsive surfaces, though they require large magnetic fields and the positioning accuracy is poor. Here, the authors propose a new strategy to manipulate nonmagnetic droplets using low magnetic fields with high positioning accuracy. Using a channeled superhydrophobic surface that enables the magnetic particle to move freely along the channel and interact with the droplet on the surface through capillary interaction, the droplet can be manipulated using a low magnetic field. When the magnetic particle is suspended in the channel, the droplet can be driven smoothly on the surface with the smallest surface friction. Increasing the magnetic field results in a stepwise motion of the transported droplet, which can be understood based on the magnetic force distribution around the magnet. Even on highly inclined surfaces, the transported droplets can self‐lock without shedding off after the removal of the magnetic field. By tuning the channel structure, 3D droplet manipulation, on‐demand droplet releasing, and multiple droplet manipulation without interference can also be realized. This versatile strategy provides an ideal platform for programming droplet behavior using magnetic fields.