title: Transient Cooperative Processes in Dewetting Polymer Melts.
abstract: We compare the high velocity dewetting behavior, at elevated temperatures, of atactic polystyrene (aPS) and isotactic polystyrene (iPS) films, with the zero shear bulk viscosity (η_{bulk}) of aPS being approximately ten times larger than iPS. As expected, for aPS the apparent viscosity of the films (η_{f}) derived from high-shear dewetting is less than η_{bulk}, displaying a shear thinning behavior. Surprisingly, for iPS films, η_{f} is always larger than η_{bulk}, even at about 50 °C above the melting point, with η_{f}/η_{bulk} following an Arrhenius behavior. The corresponding activation energy of ∼160±10  kJ/mol for iPS films suggests a cooperative motion of segments which are aligned and agglomerated by fast dewetting.
authors.affiliation: Institute of Physics, Albert Ludwig University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Sivasurender
authors.initials: S
authors.lastname: Chandran
authors.affiliation: Institute of Physics, Albert Ludwig University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Reiter