(24g) Magneto-Capillary Dynamics of Amphiphilic Janus Particles at Curved Liquid Interfaces

It is commonly held that static homogenous fields cannot be used to drive the translational motions of magnetic colloids. Such field can exert no net force but torque on a colloidal particle. However, by coupling particle orientation to its position on a curved interface, even static homogenous fields can be used to drive rapid particle motions. Here, we demonstrate this effect using magnetic Janus particles with amphiphilic surface chemistry adsorbed at spherical interface of a water drop in decane. The particles move along the drop surface to align their magnetic moments parallel to the applied field, as explained quantitatively by a model that accounts for the magnetic torque on the particle and the constraints imposed by the interface. Notably, the effective magnetic force experienced by particles adsorbed on small drops can be many orders of magnitude larger than those due to field gradients. This mechanism may be useful in creating highly responsive emulsions and foams stabilized by magnetic particles.