title: Observation of dynamical heterogeneities and their time evolution on the surface of an amorphous polymer.
abstract: Although the formation of dynamic heterogeneities in glass-forming materials is believed to play an essential role in determining their properties as the glass transition is approached, direct imaging of these heterogeneities remains a challenge. Here, we report on a direct observation of nanoscale dynamic heterogeneities and their time evolution over ~10(3) s on the surface of a glassy polymer, polystyrene (PS), using atomic force microscopy with a 1 nm radius tip. The length scale of these heterogeneities was measured to be ~2.1 nm and the lifetime was determined to be ~10(2) s, in agreement with the length and time scales of heterogeneous dynamics reported for bulk polymers around the glass transition. These results are consistent with the existence of a very thin liquid-like layer at the glassy polymer surface. The validity of the method is confirmed by comparing the properties of surface dynamics of neat and plasticized films.
authors.affiliation: WPI-Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan. knakaji@wpi-aimr.tohoku.ac.jp.
authors.forename: Hung K
authors.initials: HK
authors.lastname: Nguyen
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Russell
authors.forename: Ken
authors.initials: K
authors.lastname: Nakajima