title: Is the reduction in tracer diffusivity under nanoscopic confinement related to a frustrated segmental mobility?
abstract: We developed an experimental method for the determination of the tracer diffusivity D(tr) in ultrathin polymer films, and the changes in the segmental mobility of tracer molecules while they diffuse through matrices of different thickness and get adsorbed onto a target substrate. D(tr) starts decreasing already at 120-150  nm and drops to 1% of its bulk value in films as thin as 7.5  nm. We discuss the results highlighting a strong decoupling between the reduction in mass transport at the nanoscale and the increase in the glass transition temperature determined via capacitive dilatometry together with a breakdown of the Stokes-Einstein relation between orientational and translational degrees of freedom.
authors.affiliation: Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium. simone.napolitano@fys.kuleuven.be
authors.forename: Simone
authors.initials: S
authors.lastname: Napolitano
authors.forename: Cinzia
authors.initials: C
authors.lastname: Rotella
authors.forename: Michael
authors.initials: M
authors.lastname: Wübbenhorst
mesh_terms: D000327:Adsorption; D002152:Calorimetry, Differential Scanning; D058266:Dielectric Spectroscopy; D004058:Diffusion; D005898:Glass / Q000737:chemistry*; D008567:Membranes, Artificial; D044367:Phase Transition; D011137:Polystyrenes / Q000737:chemistry*; D013499:Surface Properties; D013997:Time Factors; D044366:Transition Temperature
chemical_list: D008567:Membranes, Artificial; D011137:Polystyrenes