文摘
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 morphologicalstructures. 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 containedpendent carboxylate groups. The complexes were formed through interactions of the carboxylates with the surfacesof the magnetite nanoparticles. The magnetite cores of the magnetite-copolymer complexes were near 10 nm indiameter, and the particles were superparamagnetic. Complexes with mass ratios of polymer to magnetite varying from50:50 to 85:15 were studied. One of our objectives is to design complexes that form stable dispersions of discreteparticles in water, yet that can be actuated (moved together) upon exposure to a uniform magnetic field. DLVOcalculations that accounted for magnetic attractive interparticle forces, as well as van der Waals, steric, and electrostaticforces are presented. Compositions were identified wherein a shallow, attractive interparticle potential minimumappears once the magnetic term is applied. This suggests that it may be possible to tune the structures of superparamagneticnanoparticle shells to allow discrete dispersions without a field, yet weak flocculation could be induced upon exposureto a field.
