title: Unusual deviations from bulk behavior in ultrathin films of poly(tert-butylstyrene): can dead layers induce a reduction of T(g)?
abstract: The temperature and thickness dependence of the thermal expansivity of ultrathin thin films of poly(tert-butylstyrene) capped between aluminum layers revealed an unusual and intriguing confinement scenario. Below 50 nm, both the glass transition temperature and the thermal expansion coefficients decreased. Such a mixed behavior implies an enhancement of the molecular mobility, without the presence of any free surface, but dead layers. On the basis of a careful analysis of averaged quantities measured by capacitive dilatometry, we deduced a profile of thermal expansivity that explains our experimental data and previous observations in polymer nanocomposites. The effect of density-conformation coupling in proximity of a nonattractive interface allows the coexistence of an immobilized fraction in direct contact with the metal and an excess of thermal expansivity, arising from the long-range effects of packing frustration penetrating inside the bulk-like core of the film.
authors.affiliation: Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium. simone.napolitano@fys.kuleuven.be
authors.forename: Simone
authors.initials: S
authors.lastname: Napolitano
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pilleri
authors.forename: Pierangelo
authors.initials: P
authors.lastname: Rolla
authors.forename: Michael
authors.initials: M
authors.lastname: Wübbenhorst