Impact dynamics of non-ferro liquid droplets under magnetic influence

Abstract

Impacting non-ferro liquid (water) droplets on a hydrophobic surface finds many applications in various sectors. Controlling droplet behavior on the impacting surface remains critically important in terms of affecting contact duration, spreading and contraction rates, and rebound height. Introducing an external magnetic influence on droplets considerably alters the impact characteristics. Consequently, the present study investigates the impacting of water droplets on hydrophobic surfaces with loosely dispersed low-surface-energy ferro particles. Since the interfacial force between the particles and water is large, a droplet picks up some ferroparticles, which are pinned on the droplet surface despite the presence of the magnetic field. The particles pinned on the droplet surface alter the droplet behavior at the impacted surface under the magnetic field. In order to assess the mechanism of how particles are picked up by the impacting droplet liquid, the particles are functionalized to reduce the surface energy. It is demonstrated that the functionalized particles are picked up by the water droplet; however, they are pinned at the droplet surface rather than being immersed into the droplet fluid. The interfacial force due to particles pinned on the droplet surface is higher than the magnetic force created under the magnetic field. This gives rise to lower contact time, droplet spreading, and rebound height. This is more pronounced at low Weber numbers.