Magnetic Control of Water Droplet Impact onto Ferrofluid Lubricated Surfaces

Abstract

Controlling the impact process of a droplet impacting a liquid film has remained a wide-open challenge. The existing passive techniques lack precise on-demand control of the impact dynamics of droplets. The present study introduces a magnet-assisted approach to control water droplets’ impact dynamics. We show that by incorporating a thin, magnetically active ferrofluid film, the overall droplet impact phenomena of the water droplets could be controlled. It is found that by modifying the distribution of the magnetic nanoparticles (MNPs) present inside the ferrofluid using a permanent magnet, the spreading and retraction behavior of the droplet could be significantly controlled. In addition to that, we also show that by altering the impact Weber number (We i), and the magnetic Bond number (Bo m), the outcomes of droplet impact could be precisely controlled. We reveal the role of the various forces on the consequential effects of droplet impact with the help of phase maps. Without the magnetic field, we discovered that the droplet impact on ferrofluid film results in no-splitting, jetting, and splashing regimes. On the other hand, the presence of magnetic field results in the no-splitting and jetting regime. However, beyond a critical magnetic field, the ferrofluid film gets transformed into an assembly of spikes. In such scenarios, the droplet impact only results in no-splitting and splashing regimes, while the jetting regime remains absent. The outcome of our study may find potential applications in chemical engineering, material synthesis, and three-dimensional (3D) printing where the control and optimization of the droplet impact process are desirable.

Directional Manipulation of Drops and Solids on a Magneto-Responsive Slippery Surface

“…In the absence of a magnetic field, the ferrofluid does not exhibit magnetization. , However, under the magnetic field, the magnetic nanoparticles align their magnetic dipoles along the magnetization of the magnetic field, resulting in magnetic interactions. Ferrofluids have found applications in several fields due to their excellent magnetic response, flexible flowability, and tunable optical and thermal properties. − The MRSS has emerged as a tool that offers to fine-tune the controlling parameters, such as the concentration of MNPs, the strength of the magnetic field, and the viscosity of the ferrofluid for manipulating liquid droplets. In one such study, a ferrofluid-cloaked droplet is deformed by a magnet (located above the droplet) approaching the droplet, resulting in droplet motion .…”