title: Incoherent neutron scattering and the dynamics of confined polycarbonate films.
abstract: Incoherent elastic neutron scattering measurements are performed on thin (75 to 1015 A) polycarbonate films supported on Si wafers. We find that the mean-square atomic displacement <u(2)> is diminished by thin film confinement. For film thicknesses comparable to the unperturbed dimensions of the macromolecule, we observe two characteristic crossover temperatures in <u(2)> as a function of temperature T, one above and the other below the bulk T(g). Furthermore, the harmonic force constant kappa, defined by the low temperature dependence of <u(2)> (i.e., kappa approximately k(B)T/<u(2)>), increases as the film thickness decreases. These observations suggest that the atoms are more strongly localized in the thin supported films.
authors.affiliation: NIST Polymers Division, Gaithersburg, Maryland 20899-8541, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Soles
authors.forename: J F
authors.initials: JF
authors.lastname: Douglas
authors.forename: W-l
authors.initials: WL
authors.lastname: Wu
authors.forename: R M
authors.initials: RM
authors.lastname: Dimeo