title: Measurement of the interior structure of thin polymer films using grazing incidence diffuse x-ray scattering.
abstract: A method is developed for calculating the small-angle x-ray scattering originating from within the interior of a thin film under grazing incidence illumination. This offers the possibility of using x-ray scattering to probe how the structure of polymers is modified by confinement. When the diffuse scattering from a thin film is measured over a range of incident angles, it is possible to separate the contributions to scattering from the interfaces and the contribution from the film interior. Using the distorted-wave Born approximation the structure factor, S(q), of the film interior can then be obtained. We apply this method to analyze density fluctuations from within the interior of a silicon supported molten polystyrene (PS) film. Measurements were made as a function of film thickness ranging from one to ten times the polymer radius of gyration (Rg). The compressibility, calculated by extrapolating the measured S(q) to q=0, agrees well with that of bulk PS for thick films, but thinner films exhibit a peak in S(q) near q=0. This peak, which grows with decreasing thickness, is attributed to a decreased interpenetration of chains and a consequent enhanced compressibility.
authors.affiliation: Department of Physics, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Mukhopadhyay
authors.forename: L B
authors.initials: LB
authors.lastname: Lurio
authors.forename: Z
authors.initials: Z
authors.lastname: Jiang
authors.forename: X
authors.initials: X
authors.lastname: Jiao
authors.forename: Michael
authors.initials: M
authors.lastname: Sprung
authors.forename: Curt
authors.initials: C
authors.lastname: DeCaro
authors.forename: S K
authors.initials: SK
authors.lastname: Sinha