title: Fluid to soft-glass transition in a quasi-2D system: thermodynamic and rheological evidences for a Langmuir monolayer.
abstract: We report an experimental study that points out the existence of a fluid to soft-glass transition in Langmuir polymer monolayers of poly(methyl methacrylate) (PMMA), for which the water/air interface behaves as a poor-solvent. The temperature dependence of surface pressure vs. surface area equilibrium isotherms shows a glass-like transition temperature at T(g,2D)≈ 298 K, significantly lower than the value for bulk PMMA (T(g,bulk)≈ 378 K). The plot of the film thickness h vs. temperature shows a sharp change of slope at about the same temperature, 298 K, which is a typical hallmark of a glass transition in thin polymer films [J. L. Keddie, R. A. L. Jones, R. A. Cory, Europhys. Lett., 1996, 27, 59-64]. Furthermore, slightly above T(g,2D), the temperature dependence of the dilational viscosity does not follow an Arrhenius law, but instead can be described by a Vogel-Fulcher-Tamman equation with parameters that are typical of a fragile glass. Not only the qualitative behavior of three distinct equilibrium and dynamic properties, but also the quantitative agreement of the values of T(g) obtained, are a strong evidence of the existence of a fluid to soft-glass transition in this quasi-2D system.
authors.affiliation: Departamento de Química Física I, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain. maestro@lps.u-psud.fr
authors.forename: Armando
authors.initials: A
authors.lastname: Maestro
authors.forename: Eduardo
authors.initials: E
authors.lastname: Guzmán
authors.forename: Raquel
authors.initials: R
authors.lastname: Chuliá
authors.forename: Francisco
authors.initials: F
authors.lastname: Ortega
authors.forename: Ramón G
authors.initials: RG
authors.lastname: Rubio
authors.forename: Reinhard
authors.initials: R
authors.lastname: Miller