A dedicated high-resolution high-throughput X-ray powder diffraction beamline has been constructed at the Advanced Photon Source (APS). In order to achieve the goals of both high resolution and high throughput in a powder instrument, a multi-analyzer detector system is required. The design and performance of the 12-analyzer detector system installed on the powder diffractometer at the 11-BM beamline of APS are presented.

The surface dynamics of supported ultrathin polystyrene films with thickness comparable to the radius of gyration were investigated by surface sensitive x-ray photon correlation spectroscopy. We show for the first time that the conventional model of capillary waves on a viscous liquid has to be modified to include the effects of a shear modulus in order to explain both static and dynamic scattering data from ultrathin molten polymer films.

The structure and proton conductivity of sulfonated styrene−ethylene copolymers have been studied. Conductivities in excess of 0.1 S/cm are obtained depending upon copolymer composition and sulfonation level. The dependence of conductivity on humidity has been measured and compared with that of Nafion and a partially sulfonated block copolymer. X-ray and neutron scattering studies suggest the presence of a bicontinuous network of hydrophilic and hydrophobic domains in water-swollen samples.

Changes to the structure of polystyrene melt films as measured through the spectrum of density fluctuations have been observed as a function of film thickness down to the polymer radius of gyration (R g ). Films thicker than 4R g show bulklike density fluctuations. Thinner films exhibit a peak in SðqÞ near q ¼ 0 which grows with decreasing thickness. This peak is attributed to a decreased interpenetration of chains resulting in an enhanced compressibility. Measurements were made using small angle x-ray scattering in a standing wave geometry designed to enhance scattering from the interior of the film compared to interface scattering. DOI: 10.1103/PhysRevLett.101.115501 PACS numbers: 61.05.cf, 68.60.Àp, 82.35.Gh A fundamental question in the theory of molecular liquids is how is their structure affected by confinement on a scale comparable to the molecular size. This is particularly relevant to polymer melts since their molecular size can extend to tens of nanometers. Improved understanding of the structure of molten polymers is of technological interest for nanoscale polymeric materials. It is also of fundamental interest as a test of basic theories of polymer fluids, and to evaluate how well these theories predict structural modifications in response to perturbations which vary over molecular length scales.Silberberg [1] advanced a hypothesis that the main effect of an interface on a polymer fluid is to reflect conformations of the polymer chains when they intersect the interface. More detailed calculations made using a range of techniques including both analytic methods [2,3] as well as Monte Carlo simulations and molecular dynamics [2-5] support Silberberg's basic conjecture. Silberberg's conjecture predicts no other change to the chain conformations. However, in films whose thickness approaches R g reflection of a chain at an interface significantly increases the local density of the coil and thus reduces the degree of entanglement. Since the chain conformation is a function of entanglement, there must be other changes beyond Silberberg's prediction. Specifically, a reduced entanglement in thin films will make the chain conformation more like a self-avoiding random walk at short length scales relative to the random walk approximated by a bulk polymer.Neutron experiments have tried to explore this issue by directly measuring the structure factor of an individual chain in a thin film. Some neutron experiments have observed an expansion of the chain structure [6,7], while other experiments find no change [8,9]. The conflicting results of these measurements may be due to the difficulty of separating surface from interior scattering. Some support for reduced interpenetration in thin films has also been found experimentally using other techniques. Tretinnikov et al. indirectly measured free volume changes in very thin films from the shift in infrared vibration bands [10]. Furthermore, free volume may play a role in the observations of a reduced glass transition temperature in thin films [11][12][13][14].To add...