title: Breakdown of the Stokes-Einstein Relation for the Rotational Diffusivity of Polymer Grafted Nanoparticles in Polymer Melts.
abstract: We report observations of breakdown of the Stokes-Einstein relation for the rotational diffusivity of polymer-grafted spherical nanoparticles in polymer melts. The rotational diffusivity of magnetic nanoparticles coated with poly(ethylene glycol) dispersed in poly(ethylene glycol) melts was determined through dynamic magnetic susceptibility measurements of the collective rotation of the magnetic nanoparticles due to imposed time-varying magnetic torques. These measurements clearly demonstrate the existence of a critical molecular weight for the melt polymer, below which the Stokes-Einstein relation accurately describes the rotational diffusivity of the polymer-grafted nanoparticles and above which the Stokes-Einstein relation ceases to apply. This critical molecular weight was found to correspond to a chain contour length that approximates the hydrodynamic diameter of the nanoparticles.
authors.affiliation: Department of Chemical Engineering, University of Florida , P.O. Box 116005, Gainesville, Florida 32603, United States.
authors.forename: Lorena
authors.initials: L
authors.lastname: Maldonado-Camargo
authors.affiliation: Department of Chemical Engineering, University of Florida , P.O. Box 116005, Gainesville, Florida 32603, United States.|J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida , P.O. Box 116131, Gainesville, Florida 32611, United States.
authors.forename: Carlos
authors.initials: C
authors.lastname: Rinaldi
keywords: Rotational diffusivity; Stokes−Einstein; dynamic magnetic susceptibility; magnetic nanoparticles