Novel triblock copolymers consisting of end blocks of polyethylene oxide (PEO) and a center block consisting of urethane and carboxylic acid groups have been shown to sterically stabilize magnetite nanoparticles that have potential drug delivery applications.(1) For these applications, it is essential to control the state of dispersion of the magnetite nanoparticles, especially with a coating of a biocompatible polymer such as PEO which can inhibit protein binding. These block copolymers adsorb on particles of magnetite, Fe3O4 approximately 10 nm in diameter via the carboxylic acid-containing center block. This leads to the formation of a PEO brush layer that sterically stabilizes the particles in an aqueous buffer solution for periods of weeks. Critical parameters that were measured included particle size with the adsorbed triblock stabilizer, the number of polymer chains/unit area bound to the particles, and the zeta potential of the particles. The hydrodynamic diameter of the polymer-magnetite complexes can be predicted using the Density Distribution model by Vagberg, et.al., that was based on the blob model for star polymers. The observed colloid stability can be related to the interparticle pair potential that governs particle dispersion by the modified Deryaguin-Landau-Verwey-Overbeek (DLVO) theory in which the steric pair interaction is modeled with a theory developed by Likos et al., based on interactions between star polymers.

(1)L. A. Harris, J. D. Goff, A. Y. Carmichael, J. S. Riffle, J. J. Harburn, T. G. St. Pierre, M. Saunders, Magnetite Nanoparticle Dispersions Stabilized with Triblock Copolymers, Chemistry of Materials, 15, 1367-1377 (2003).