title: Aqueous dispersions of magnetite nanoparticles complexed with copolyether dispersants: experiments and theory.
abstract: Magnetite (Fe3O4) nanoparticles have been synthesized and complexed with carboxylate-functional block copolymers, and then aqueous dispersions of the complexes were investigated as functions of their chemical and morphological structures. The block copolymer dispersants had either poly(ethylene oxide), poly(ethylene oxide-co-propylene oxide), or poly(ethylene oxide-b-propylene oxide) outer blocks, and all of them had a polyurethane center block that contained pendent carboxylate groups. The complexes were formed through interactions of the carboxylates with the surfaces of the magnetite nanoparticles. The magnetite cores of the magnetite-copolymer complexes were near 10 nm in diameter, and the particles were superparamagnetic. Complexes with mass ratios of polymer to magnetite varying from 50:50 to 85:15 were studied. One of our objectives is to design complexes that form stable dispersions of discrete particles in water, yet that can be actuated (moved together) upon exposure to a uniform magnetic field. DLVO calculations that accounted for magnetic attractive interparticle forces, as well as van der Waals, steric, and electrostatic forces are presented. Compositions were identified wherein a shallow, attractive interparticle potential minimum appears once the magnetic term is applied. This suggests that it may be possible to tune the structures of superparamagnetic nanoparticle shells to allow discrete dispersions without a field, yet weak flocculation could be induced upon exposure to a field.
authors.affiliation: The Macromolecules and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.forename: M Shane
authors.initials: MS
authors.lastname: Thompson
authors.forename: Anita Y
authors.initials: AY
authors.lastname: Carmichael-Baranauskas
authors.forename: Beth L
authors.initials: BL
authors.lastname: Caba
authors.forename: Michael A
authors.initials: MA
authors.lastname: Zalich
authors.forename: Yin-Nian
authors.initials: YN
authors.lastname: Lin
authors.forename: O Thompson
authors.initials: OT
authors.lastname: Mefford
authors.forename: Richey M
authors.initials: RM
authors.lastname: Davis
authors.forename: Judy S
authors.initials: JS
authors.lastname: Riffle
mesh_terms: D052203:Ferrosoferric Oxide / Q000737:chemistry*; D008280:Magnetics; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D011108:Polymers; D052203:Ferrosoferric Oxide