title: Facile Assembly of Aligned Magnetic Nanoparticle Chains in Polymer Nanocomposite Films by Magnetic Flow Coating.
abstract: Magnetic nanoparticle chains are found in biosystems, such as in the brain of migratory birds. Inspired by natural assemblies, in a novel approach, the facile assembly of magnetically aligned polymer grafted cobalt nanoparticle (MPGNP) chains in thin polymer films was accomplished by using low strength permanent magnets directly during the flow-casting process. Unlike previous studies of MPGNP chain alignment in the high viscosity melt phase, the high mobility of such dispersed MPGNPs during casting by magnetic flow coating of polystyrene (PS) nanocomposite thin films from a dispersion allowed for formation of well-aligned MPGNP chains at the PS film/air interface. Both spherical (symmetric) and cylindrical (asymmetric) MPGNP aligned chains were obtained with distinct properties. The average chain length and width, number of particles per chain, spacing between parallel chains, and chain alignment were quantified using surface probe and electron microscopy, and grazing incidence X-ray. The aligned chains did not randomize when annealed above the film glass temperature, apparently due to the high translational entropic barrier for macroscopic (GISAXS) chain realignment. The Young's bending modulus of the aligned MPGNP nanocomposite films as revealed by a thin film wrinkling metrology showed that the elastic modulus along the chain axis direction was higher for the film with the cylindrical but not the spherical MPGNP chains. This suggests that PGNP chain flexural properties depend on asymmetry of the local MPGNP unit, much like the persistence length "stiffness" effect of polymer chains. The ferromagnetic nature of the aligned PGMNP chains resulted in film rotation, as well as repulsive and attractive translation under an applied external magnetic field. Such magnetically responsive films can be useful for sensors and other applications.
authors.affiliation: Department of Polymer Engineering, The University of Akron , Akron, Ohio 44325, United States.
authors.forename: Hongyi
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Department of Polymer Engineering, The University of Akron , Akron, Ohio 44325, United States.
authors.forename: Irina J
authors.initials: IJ
authors.lastname: Zvonkina
authors.affiliation: Chemistry Department, Faculty of Science, King Saud University , PO Box 2455, Riyadh 11451, Saudi Arabia.
authors.forename: Abdullah M
authors.initials: AM
authors.lastname: Al-Enizi
authors.affiliation: Materials Science and Technology Program, College of Arts and Sciences, Qatar University , PO Box 2713, Doha, Qatar.|Polymer Materials Research Department, Advanced Technology and New Materials Research Institute, City for Scientific Research and Technology Applications , New Borg El-Arab City, P.O. Box: 21934, Alexandria, Egypt.
authors.forename: Ahmed A
authors.identifier: http://orcid.org/0000-0002-7291-5723
authors.initials: AA
authors.lastname: Elzatahry
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona , Tucson, Arizona 85721, United States.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Pyun
authors.affiliation: Department of Polymer Engineering, The University of Akron , Akron, Ohio 44325, United States.
authors.forename: Alamgir
authors.initials: A
authors.lastname: Karim
keywords: magnetic alignment; magnetic nanoparticles; polymer nanocomposite films; self-assembly; thin films