Effects of vertical magnetic field on impact dynamics of ferrofluid droplet onto a rigid substrate

Ferrofluid as a smart fluid has a wide range of applications. Although the spreading dynamics of water droplets have been well investigated, spreading dynamics of ferrofluid droplets under a magnetic field has rarely been studied. This paper reports our findings of the impact dynamics of a ferrofluid droplet onto a tempered glass surface in the presence of a vertical magnetic field. The effects of magnetic intensity, impact velocity, and Fe3O4 nanoparticle concentration were investigated. It turned out that with the increased magnetic intensity, the height of the ferrofluid droplet would decrease owing to the energy dissipation increase of ferrofluids under a magnetic field and the additional stretching force in the vertical direction. Interestingly, we found that exertion of the magnetic field could significantly diminish the influence of velocity differences on the droplet spread dynamics in height direction. Satellite droplets were also observed in certain cases when the rebound kinetic energy could overcome the restraint of surface tension and adhesion of viscosity in the presence of the magnetic field. Our work will be a significant reference to with regard to various practical applications, especially when the impact dynamics of ferrofluid droplets need to be under precise control, for instance, as in three-dimensional printing or spray coating, etc.