We describe and illustrate a forward modeling method for quantitatively reconstructing the geometry and orientation of microstructural features inside of bulk samples from high energy x-ray diffraction microscopy data. Data sets are comprised of CCD images of Bragg diffracted beams originating from individual grains in a thin planar section of sample. Our analysis approach first reduces the raw images to a binary data set in which peaks have been thresholded at a fraction of their height after noise reduction processing. We then use a computer simulation of the measurement and the sample microstructure to generate calculated diffraction patterns over the same range of sample orientations used in the experiment. The crystallographic orientation at each of an array of area elements in the sample space is adjusted to optimize overlap between experimental and simulated scattering. In the present verification exercise, data are collected at the Advanced Photon Source beamline 1-ID using microfocused 50keV x-rays. Our sample is a thin silicon wafer. By choosing the appropriate threshold fraction and convergence criteria, we are able to reconstruct to ≤ 10µm errors the sub-region of the silicon wafer that remains in the incident beam throughout the rotation range of the measurement. The standard deviation of area element orientations is ≈ 0.3 degrees. Our forward modeling approach offers a degree of noise immunity, is applicable to polycrystals and composite materials, and can be extended to include scattering rules appropriate for defected materials.

No abstract

A series of copolymers was designed and synthesized to elucidate the nature of bisphenol A polycarbonate (BPA-PC) -relaxation. Specifically, the investigation was focused on the extent of cooperativity and the origin of this cooperative motion. The structure of bisphenol A polycarbonate was modified to different extents by inserting units of bulkier monomer analogue, tetramethylbisphenol A, into the polymer main chain at regular intervals. The dynamic mechanical relaxation technique was used to follow the change of relaxation behavior of the copolymers. The dynamic mechanical spectra of the synthesized homologues suggest that the intrachain interactions are the dominant factor of this cooperative relaxation and the extent of the cooperation is about seven repeat units. These results may explain why BPA-PC has such outstanding ductility.

Dynamic mechanical-loss spectra at 1 Hz, and dipolar rotational spin-echo 13C NMR spectra at 15.1 MHz, have been obtained for a series of copolymers of polycarbonate made from monodisperse oligomers of Bisphenol A polycarbonate (B X ), alternating (via connecting carbonate linkages) with single units of 3,3‘,5,5‘-tetramethylbisphenol A (T). The mechanical-loss relaxation of B X T suggests cooperative motions in the copolymer glass at T = −100 and −20 °C. The NMR results indicate that no phenylene rings undergo π flips in T units and that most but not all of the B rings flip faster than 10 kHz at 300 K. A necessary but not sufficient condition to constrain a B ring from flipping in B X T is the presence of both interchain and intrachain T-unit nearest neighbors. These results are interpreted in terms of a packing model for polycarbonate-like systems that emphasizes the importance for chain dynamics of the proximity and cooperative motion of nearest-neighbor chains having similar local orientational order.

In the absence of solvent, highly selective hydrogenation of o-chloronitrobenzene and m-chloronitrobenzene, with selectivity to the corresponding chloroanilines of ≥99.4% and complete conversion of the substrates, was realized over a robust Pt/Fe(3)O(4) catalyst which was prepared by adsorbing Pt nanoclusters on a Fe(3)O(4) support.