Motion, deformation and pearling of ferrofluid droplets due to a tunable moving magnetic field.

We demonstrate unique evolutions of the shape of ferrofluid droplets during their motion over horizontal and inclined planes assisted by an applied field. We substantially extend the basic study regarding the motion of the ferrofluid droplets to address state-of-the-art parametric variation. While doing so, we describe some uncommon phenomena such as pearling, which has not been reported to date in connection with the motion of ferrofluid droplets. The contact angle varies dynamically with the motion of the droplet over horizontal and inclined planes. The shape of the ferrofluid droplet evolves continuously with the variation of different parameters. The spheroidal shape transforms into oblate, pear shape and tear drop with a symmetric corner and finally tears into daughter globules, famously known as pearling. The field strength, magnet velocity and concentration of nanoparticles control the motion, deformation and pearling. We emphasize that pearling is predominant during horizontal translation and depreciates during the ascent of an inclined plane (due to the resolved component of gravity). From a scale analysis, we demonstrate that the deformation and pearling can be predicted in terms of the magnetic Bond number, magnetic Laplace number and Bond number.