Shaping the Assembly of Superparamagnetic Nanoparticles

Abstract

Superparamagnetism exists only in nanocrystals, and to endow micro/macro-materials with superparamagnetism, superparamagnetic nanoparticles have to be assembled into complex materials. Most techniques currently used to produce such assemblies are inefficient in terms of time and material. Herein, we used evaporation-guided assembly to produce superparamagnetic supraparticles by drying ferrofluid droplets on a superamphiphobic substrate in the presence of an external magnetic field. By tuning the concentration of ferrofluid droplets and controlling the magnetic field, barrel-like, cone-like, and two-tower-like supraparticles were obtained. These assembled supraparticles preserved the superparamagnetism of the original nanoparticles. Moreover, other colloids can easily be integrated into the ferrofluid suspension to produce, by co-assembly, anisotropic binary supraparticles with additional functions. Additionally, the magnetic and anisotropic nature of the resulting supraparticles was harnessed to prepare magnetically actuable microswimmers.

Magnetic Nanoparticle Systems for Nanomedicine—A Materials Science Perspective

“…As a consequence, the MNPs accumulate at the ferrofluid drop-water interface, resulting in strongly non-spherical shape nanocomposite particles [39]. Magnetic field guided evaporation of ferrofluid droplets [78,79], making use of specific Rosensweig instabilities and tuning the concentration of ferrofluid, allows for preparing various shaped nanocomposites (so-called "supraparticles") and also preserving superparamagnetic behavior. The high evaporation rate organic ferrofluids having oleic acid monolayer coated magnetite NPs were used to fabricate magnetoactive fibrous nanocomposites and multi-responsive co-networks [80,81], which exhibit promising characteristics for magnetothermally or pH triggered drug delivery.…”

Flexible Ferrofluids: Design and Applications

“…Apart from ferrofluid‐derived microneedles, the fabrication of micro‐/macrosized 3D superparamagnetic particles based on ferrofluid has been reported recently . These supraparticles were generated via an evaporation‐directed self‐assembly by fixing ferrofluid droplets on a superamphiphobic surface and drying them under an external magnetic field ( Figure a).…”

“…c) Disassembly and assembly of supraparticles: i) disassembled supraparticles with long interparticle distance; ii) supraparticles assembled into complex structures when the interparticle distance decreases. a–c) Reproduced with permission . Copyright 2019, American Chemical Society.…”

Magnetoresponsive Surfaces for Manipulation of Nonmagnetic Liquids: Design and Applications

“…Funct. [94][95][96][97] These magnetic interactions can be used for active control of liquid motion on surfaces. 2020, 30,1906507 [81] Copyright 2015, American Chemical Society.…”

“…[94,95] On a ferrofluid-infused porous surface, a perpendicular magnetic field can trigger the formation of rough surface structures. [94,95] On a ferrofluid-infused porous surface, a perpendicular magnetic field can trigger the formation of rough surface structures.…”