title: Control of magnetite primary particle size in aqueous dispersions of nanoclusters for high magnetic susceptibilities.
abstract: Aqueous dispersions of iron oxide nanoparticles with a high initial magnetic susceptibility (χi) are of interest as contrast agents in electromagnetic tomography. Nanoclusters composed of iron oxide primary particles were formed by co-precipitation of Fe(II) and Fe(III) chlorides at alkaline conditions and high temperature of 95°C. Two-step addition of citrate was used to produce large primary particles and then stabilize the nanoclusters. The size of the primary particles was tuned from 5nm to 15nm by varying the citrate/iron precursor ratio during the normal phase hydrolysis reaction, while the second iteration of citrate stabilized the nanoclusters with hydrodynamic diameters of 30-75nm. The crystallinity of the iron oxide nanoparticles was promoted by annealing at 95°C and systematically studied with Superconducting Quantum Interference Device (SQUID), Vibrating Sample Magnetometer (VSM), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The dependence of χi was examined over a range of low volume fractions (0.005<θ<0.02) to understand the magnetic behavior of dispersions. The χi of the dispersions increased markedly with the size and concentration of the constituent primary particles, reaching an unusually high value of 0.85 at 1.6% v/v for 15nm primary particles, which is 2-3 times higher than that for typical commercial ferrofluids. The high χi values are favored by the high crystallinity and the large magnetic diameter of 9.3nm, indicating a relatively thin surface nonmagnetic layer where the spin orientations are disordered.
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Ki Youl
authors.initials: KY
authors.lastname: Yoon
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Xue
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Yunping
authors.initials: Y
authors.lastname: Fei
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Jae Ho
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Victoria
authors.initials: V
authors.lastname: Cheng
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Hitesh G
authors.initials: HG
authors.lastname: Bagaria
authors.affiliation: Department of Petroleum and Geosystems Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Chun
authors.initials: C
authors.lastname: Huh
authors.affiliation: Department of Petroleum and Geosystems Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Steven L
authors.initials: SL
authors.lastname: Bryant
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Seong Deok
authors.initials: SD
authors.lastname: Kong
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Vincent W
authors.initials: VW
authors.lastname: Ngo
authors.affiliation: Department of Petroleum and Geosystems Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Amir-Reza
authors.initials: AR
authors.lastname: Rahmani
authors.affiliation: Advanced Energy Consortium & Bureau of Economic Geology, University of Texas at Austin, TX 78758, United States.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Ahmadian
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ellison
authors.affiliation: Department of Chemical Engineering, University of Texas at Austin, TX 78712, United States. Electronic address: kpj@che.utexas.edu.
authors.forename: Keith P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D057446:Hydrodynamics; D006868:Hydrolysis; D060328:Magnetic Phenomena; D058185:Magnetite Nanoparticles / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D011789:Quantum Theory; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D058185:Magnetite Nanoparticles; D014867:Water
keywords: Aqueous dispersion; Colloidal stability; Electromagnetic imaging; Magnetic susceptibility; Magnetite; Superparamagnetic nanoparticles