title: Triggered self-assembly of magnetic nanoparticles.
abstract: Colloidal magnetic nanoparticles are candidates for application in biology, medicine and nanomanufacturing. Understanding how these particles interact collectively in fluids, especially how they assemble and aggregate under external magnetic fields, is critical for high quality, safe, and reliable deployment of these particles. Here, by applying magnetic forces that vary strongly over the same length scale as the colloidal stabilizing force and then varying this colloidal repulsion, we can trigger self-assembly of these nanoparticles into parallel line patterns on the surface of a disk drive medium. Localized within nanometers of the medium surface, this effect is strongly dependent on the ionic properties of the colloidal fluid but at a level too small to cause bulk colloidal aggregation. We use real-time optical diffraction to monitor the dynamics of self-assembly, detecting local colloidal changes with greatly enhanced sensitivity compared with conventional light scattering. Simulations predict the triggering but not the dynamics, especially at short measurement times. Beyond using spatially-varying magnetic forces to balance interactions and drive assembly in magnetic nanoparticles, future measurements leveraging the sensitivity of this approach could identify novel colloidal effects that impact real-world applications of these nanoparticles.
authors.affiliation: Smart State Center for Experimental Nanoscale Physics and Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA.|Present Address: MagAssemble LLC, Irmo, SC 29063 USA.
authors.forename: L
authors.initials: L
authors.lastname: Ye
authors.affiliation: Smart State Center for Experimental Nanoscale Physics and Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: T
authors.initials: T
authors.lastname: Pearson
authors.affiliation: Center for Optical Materials Science and Engineering Technologies (COMSET) and Department of Materials Science and Engineering, Clemson University, 161 Sirrine Hall, Clemson, SC 29634 USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Cordeau
authors.affiliation: Center for Optical Materials Science and Engineering Technologies (COMSET) and Department of Materials Science and Engineering, Clemson University, 161 Sirrine Hall, Clemson, SC 29634 USA.
authors.forename: O T
authors.initials: OT
authors.lastname: Mefford
authors.affiliation: Smart State Center for Experimental Nanoscale Physics and Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Crawford