Synthesis of iron oxide nanoparticles under oxidizing environment and their stabilization in aqueous and non-aqueous media

Aqueous magnetic fluids were synthesized by a sequential process involving the chemical coprecipitation of Fe(II) and Fe(III) salts with ammonium hydroxide (NH4OH) followed by resuspension of the ultrafine particles in water using fatty acids. This procedure produced Fe3O4 nanoparticles stabilized against agglomeration by bilayers of n-alkanoic acids with 9−13 carbons encapsulating the metal particles. The magnetic properties and particle size and size distributions of these magnetic fluids, characterized by transmission electron microscopy and superconducting quantum interference device, indicated the formation of single-domain nanoparticles of mean diameter ∼9.3 and ∼7.5 nm, respectively; the difference in values determined by the two methods implies the presence of a nonmagnetic layer on the particle surface. Thermogravimetric analysis measurements showed the existence of two distinct populations of surfactants on the particle surface, each having surfactant coverage of ∼21−24 A2/molecule, that was con...

Bilayer Surfactant Stabilized Magnetic Fluids: Synthesis and Interactions at Interfaces

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Magnetite nanoparticles display strong ferrimagnetic behavior and are less sensitive to oxidation than magnetic transition metal nanoparticles such as cobalt, iron, and nickel. For in vivo applications, well-defined organic coatings are needed to surround the magnetite nanoparticles and prevent any aggregation. The goal of this research was to develop complexes of magnetite nanoparticles coated with well-defined hydrophilic polymers so that they could be dispersed in aqueous fluids. Focal points have included the following:  (1) Investigations of polymer systems that bind irreversibly to magnetite at the physiological pH, (2) the design of block copolymers with anchor and tail blocks to enable dispersion in biological fluids, and (3) investigations of copolymer block lengths to maximize the concentration of bound magnetite. Hydrophilic triblock copolymers with ...

Magnetite Nanoparticle Dispersions Stabilized with Triblock Copolymers

Fe3O4 nanoparticles coated with oleic acid bilayer (a diameter about 12 nm) were synthesized. The structure and composition of the particles were analyzed by TEM, FTIR and TGA. The TGA experiments of the bilayer-coated particles show a distinct two-stage mass loss. Partition experiments show that the modified Fe3O4 nanoparticles are affected by aqueous dispersion pH and ion strength. Accordingly, the Pickering emulsions stabilized by modified Fe3O4 particles are also sensitive to pH and ion strength. The phase inversion of the emulsions occurs when 1.00 pH 12.05 , and no phase inversion occurs after complete desorption of the second layer surfactants when pH > 13.50 . The phase inversion of emulsions also can be adjusted by the ion strength. In interfacial adsorption experiments, the hydrophobic Fe3O4 nanoparticles form particle clusters, while the hydrophilic particles form uniform multilayers.

Synthesis of bilayer oleic acid-coated Fe3O4 nanoparticles and their application in pH-responsive Pickering emulsions

Immobilization of albumin on aminosilane modified superparamagnetic magnetite nanoparticles and its characterization

The development of sink-float separators for materials of different densities, which utilize the levitation force of magnetic fluid, have been recently reported. The system usually consists of an electromagnet, separation cell, equipment for recovery of magnetic fluid smeared on the separated products, and controlling system. This paper describes and discusses the construction of sink-float separators using permanent magnets and provides test results for artificial mixtures of nonferrous metals. Ferrite magnet and rare-earth cobalt magnet were used as magnetic field generators in two separators. One for separating aluminum from other nonmagnetic metals, and the other to separate copper, zinc and lead from each other. A series of tests were performed on samples of 6 to 30 mm size, and it was found that the separators operated as expected. The separation of finer metals, however, proved difficult due to the attractive force which acts between nonmagnetic bodies immersed in magnetic fluid in a magnetic field. The chemical process to recover the magnetic fluid from smeared separation products is also proposed.

K. Nakatsuka

Papers

Sink-float separators using permanent magnets and water based magnetic fluid

Correction to "Sink-float separators using permanent magnets and water based magnetic fluid"