Imaging magnetic flux lines with iron oxide nanoparticles using a “fossilized liquid assembly”

Abstract

Directed self-assembly of nanomaterials via external fields is an attractive processing tool for industry as it is inherently inexpensive and flexible. Direct observations of this process are however challenging due to the nano and meso length scales involved. The self-assembly of magnetic nanoparticles in particular has gained much recent interest for applications ranging from biomedical imaging and targeted cancer therapy to ferrofluid mechanical damping devices, that rely on the state of aggregation and alignment of the nanoparticles. We utilize an oil-water platform to directly observe directed selfassembly of magnetic nanoparticles that are field ordered into two-dimensional mesostructures through the fossilized liquid assembly (FLA) method. Our system consisted of polymer-coated iron-oxide nanoparticles (25 nm) which were assembled in the vicinity of the interface between a crosslinkable hydrophobic monomer (UV-polymerizable) oil, and water through the use of external magnetic fields, and then cured with UV light. This flash curing system effectively provides a snapshot of the assembly process and allows for direct visualization of assemblies through the use of both atomic force and optical microscopy. In this study, entire magnetic flux field lines in various geometrical configurations were successfully modelled and mapped out by the magnetic nanoparticles, both in-plane and in perpendicular orientations utilizing FLA. The assemblies showed strong directional selectivity and alignment with the flux field lines and provided evidence of strong dipole interactions which partially caused aggregate sedimentation.

Facile Assembly of Aligned Magnetic Nanoparticle Chains in Polymer Nanocomposite Films by Magnetic Flow Coating

“…Our previous studies have demonstrated the effect of the magnetic field strength and the average nanoparticle agglomeration area and morphology when organized at an oil–water liquid–liquid interface by a method termed “Fossilized Liquid Assembly (FLA)”. ,− By removal of one (water) liquid phase, and embedding the particles in the other (oil) phase by its polymerization with UV light, such nanostructures protruding from the air/film surface were observed under an applied magnetic field. The shape and the morphology of such magnetic field induced agglomerate structures can also decrease the total Gibbs energy of the system at the liquid–liquid interface.…”

Self assembly of magnetic nanoparticles at silicon surfaces

“…In an external magnetic field the magnetic moments of individual particles orient along the field lines, while dipolar interactions simultaneously lead to field-induced ordering. 3 This results, for example in magneto-rheological and other properties which are of strong interest as the viscosity sensitively depends on external magnetic fields. 4 In particular, under the influence of shear, a torque is applied to the particles, leading to a field-induced viscosity anisotropy, as has been observed in a ferrofluid based on nanodisc cobalt particles.…”

Enhancement of infrared absorption through a patterned thin film of magnetic field and spin-coating directed self-assembly of gold nanoparticle stabilised ferrofluid emulsion

“…During magnetic field directed self-assembly, the dipole–dipole interaction between magnetic particles or magnetic fluid droplets builds arrays of chain-like clusters that can span over a long distance at the microscale along the generated flux lines of the magnetic source. 28,29 The density of these flux lines is dependent on both the size and strength of the magnetic field; 30 therefore, the chain length, thickness, and gaps between them can be controlled by suitably selecting the magnetic field strength, orientation, and distance from the subject. Additionally, these arrays of chains must be immobilized on the substrate, either by drying or curing an aqueous polymer.…”