title: Cooperative strings and glassy interfaces.
abstract: We introduce a minimal theory of glass formation based on the ideas of molecular crowding and resultant string-like cooperative rearrangement, and address the effects of free interfaces. In the bulk case, we obtain a scaling expression for the number of particles taking part in cooperative strings, and we recover the Adam-Gibbs description of glassy dynamics. Then, by including thermal dilatation, the Vogel-Fulcher-Tammann relation is derived. Moreover, the random and string-like characters of the cooperative rearrangement allow us to predict a temperature-dependent expression for the cooperative length ξ of bulk relaxation. Finally, we explore the influence of sample boundaries when the system size becomes comparable to ξ. The theory is in agreement with measurements of the glass-transition temperature of thin polymer films, and allows quantification of the temperature-dependent thickness hm of the interfacial mobile layer.
authors.affiliation: Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada N2L 2Y5; Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI ParisTech, PSL Research University, 75005 Paris, France; thomas.salez@espci.fr jforrest@perimeterinstitute.ca.
authors.forename: Thomas
authors.initials: T
authors.lastname: Salez
authors.affiliation: Laboratoire de Probabilités et Modèles Aléatoires, Université Paris Diderot, 75013 Paris, France;
authors.forename: Justin
authors.initials: J
authors.lastname: Salez
authors.affiliation: Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI ParisTech, PSL Research University, 75005 Paris, France; Department of Physics and Astronomy, McMaster University, Hamilton, ON, Canada L8S 4M1;
authors.forename: Kari
authors.initials: K
authors.lastname: Dalnoki-Veress
authors.affiliation: Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI ParisTech, PSL Research University, 75005 Paris, France;
authors.forename: Elie
authors.initials: E
authors.lastname: Raphaël
authors.affiliation: Perimeter Institute for Theoretical Physics, Waterloo, ON, Canada N2L 2Y5; Department of Physics & Astronomy, University of Waterloo, Waterloo, ON, Canada N2L 3G1 thomas.salez@espci.fr jforrest@perimeterinstitute.ca.
authors.forename: James A
authors.initials: JA
authors.lastname: Forrest
keywords: cooperative rearrangement; glass transition; thin films