title: A direct quantitative measure of surface mobility in a glassy polymer.
abstract: Thin polymer films have striking dynamical properties that differ from their bulk counterparts. With the simple geometry of a stepped polymer film on a substrate, we probe mobility above and below the glass transition temperature Tg. Above Tg the entire film flows, whereas below Tg only the near-surface region responds to the excess interfacial energy. An analytical thin-film model for flow limited to the free surface region shows excellent agreement with sub-Tg data. The system transitions from whole-film flow to surface localized flow over a narrow temperature region near the bulk Tg. The experiments and model provide a measure of surface mobility in a simple geometry where confinement and substrate effects are negligible. This fine control of the glassy rheology is of key interest to nanolithography among numerous other applications.
authors.affiliation: Department of Physics and Astronomy and Guelph-Waterloo Physics Institute, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Chai
authors.forename: T
authors.initials: T
authors.lastname: Salez
authors.forename: J D
authors.initials: JD
authors.lastname: McGraw
authors.forename: M
authors.initials: M
authors.lastname: Benzaquen
authors.forename: K
authors.initials: K
authors.lastname: Dalnoki-Veress
authors.forename: E
authors.initials: E
authors.lastname: Raphaël
authors.forename: J A
authors.initials: JA
authors.lastname: Forrest