Manipulation of Ferrofluid‐Wrapped Drops: Translation, Coalescence, and Release

Abstract

Magnetic manipulation of droplets has emerged as a promising strategy to achieve several complex tasks ranging from targeted drug delivery and micro‐robotics to controlled chemical synthesis. Hence, proper control in creating magnetically responsive droplets is indispensable for successful implementation. Here, an impact‐based encapsulation technique is employed to create stable ferrofluid‐wrapped single‐liquid and compound droplets inside a water bath. Thereafter, a permanent magnet is used to manipulate the resulting encapsulated cargo and demonstrate its feasibility for various applications. The manipulations reported herein are underwater magnet‐assisted drop translation and coalescence of compound droplets. The release of the innermost cargo in the compound droplet is also experimentally demonstrated via magnetic actuation. Importantly, for the first time, magnetically controlled coalescence of ferrofluid encapsulated compound droplets containing water‐soluble species in a water pool is demonstrated. The non‐contact manipulation technique presented in this work promises significant implications for magnet‐assisted actuation technologies.

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

“…The film thickness reduces after continuous draining, and the van der Waals force comes into play, resulting in the rupture of the thin film and the merging of the two droplets. It can be mentioned that the drainage of the ferrofluid film at the point of contact (of two drops) can be controlled using a strong magnetic field, as observed in one of our works . The experimental video corresponding to the coalescence of DI water and the EG drop can be found in the Supporting Information (Movie S3).…”

“…It can be mentioned that the drainage of the ferrofluid film at the point of contact (of two drops) can be controlled using a strong magnetic field, as observed in one of our works. 40 The experimental video corresponding to the coalescence of DI water and the EG drop can be found in the Supporting Information (Movie S3). Based on this demonstration, we have performed proof-of-concept experiments to demonstrate the microchemical reactions depicted in the next section.…”

“…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 .…”

Switchable Wettability States of a Ferrofluid Droplet atop a Hydrophobic Interface

“…A substantial collection of scholarly work has previously been reported on the interfacial dynamics and its characterization of ferrofluid droplets. − Guo et al focused on examining the impact of magnetic fields on ferrofluid droplets positioned on a modified hydrophobic surface. They observed that the presence of superhydrophobic surfaces enhances the mobility of ferrofluid droplets as a result of their reduced surface energy and restricted adhesion.…”