Remote-controlled deposit of superparamagnetic colloidal droplets

Evaporation of sessile droplets is a way to organize suspended particles and create surface coating. Many studies have demonstrated that suspensions with various compositions can give rise to qualitatively different dried patterns, often by focusing on the radial density profile of deposited particles. We demonstrate that a single suspension of superparamagnetic colloids can give rise to several dried patterns thanks to an external magnetic field applied during the evaporation process. We show the various patterns obtained with zero, constant, rotating, and oscillating magnetic fields, and evidence the continuous control given by the intensity of a constant magnetic field. We also show that this magnetic control has a substantial effect on the morphological details of the deposits.