Shaping of sessile magnetic drops due to electromagnetic stress.

While electric fields have been widely studied for drop shaping and digital microfluidics, a unified electromagnetic approach inclusive of magnetic fields is by far less known. Here using the electromagnetic stress tensor, we derive the stress acting on a droplet and test the results experimentally by measuring the shape of a paramagnetic drop in a magnetic field. We show through a simple transformation that our model can be applied to shaping of droplets by electric fields, thus giving a holistic description of the electromagnetic stresses acting on drops. This provides a blueprint for controlled shaping of sessile magnetic drops and has application to magnetic technologies in displays, liquid lenses, and chemical mixing of drops in microfluidics.