Perspective: Ferromagnetic Liquids

Abstract

Mechanical jamming of nanoparticles at liquid–liquid interfaces has evolved into a versatile approach to structure liquids with solid-state properties. Ferromagnetic liquids obtain their physical and magnetic properties, including a remanent magnetization that distinguishes them from ferrofluids, from the jamming of magnetic nanoparticles assembled at the interface between two distinct liquids to minimize surface tension. This perspective provides an overview of recent progress and discusses future directions, challenges and potential applications of jamming magnetic nanoparticles with regard to 3D nano-magnetism. We address the formation and characterization of curved magnetic geometries, and spin frustration between dipole-coupled nanostructures, and advance our understanding of particle jamming at liquid–liquid interfaces.

Ferromagnetic liquid droplets with adjustable magnetic properties

“…We stress that this terminology is motivated by magnetic properties and does not infer mechanical jamming of all layers from a chemical point of view. The capacity of the FMLD to form magnetic surfactant multilayers is highly dependent on the ligand functionalization (10), which is in support of the current interpretation of a magnetic stray field-induced assembly.…”

“…3C) and numerical modeling (Fig. 3B) (10). In fact, the hydrodynamic angular frequency of all investigated FMLDs is at least one order of magnitude lower than the driving frequency ω0.…”

“…Experimentally, we observed the transition from unjammed to partially and completely jammed interfaces in the form of the structural deformation of the initial and final spherical droplet in the presence of a rotating magnetic field (Fig. 2D) due to spatial variations in rigidity, magnetization, and magnetic in-surface anisotropy driven by magnetic dipole interactions within the magnetic NP-surfactant layer (10).…”

“…For perfect spherical NPs without magneto-crystalline or shape anisotropy, the surfactant layer would exhibit an insurface magnetic anisotropy with magnetization and, to a great extent, magnetic stray fields confined to the interface (Fig. 1A) (10). A more realistic picture is the random distribution of NP shape, size, and crystal axes orientation (Fig.…”

“…ferromagnetic liquid droplet | magnetic nanoparticle-surfactants | liquid-liquid interface | self-assembly | 3D nanomagnetism L iquid-liquid interfaces act as traps to molecular surfactants (1, 2), polyelectrolytes (3,4), biomaterials (5), and microparticles/nanoparticles (NPs) (6, 7) that reduce the interfacial energy (6) and endow the interface with their inherent properties. This functionalization enables novel magnetic (8)(9)(10), optical (11)(12)(13), electric response (14,15), and bio-inspired (16) materials. The particles jammed at the interface provide the system with high stability against deformation and coalescence, which is relevant for applications like encapsulation for drug delivery and fluidic reactors (17,18).…”