Synchrotron Source X-ray Diffraction Research Articles

Unique Difference in Transition Temperature of Two Similar Fluorinated Side Chain Polymers Forming Hexatic Smectic Phase: Poly{2-(perfluorooctyl)ethyl acrylate} and Poly{2-(perfluorooctyl)ethyl vinyl ether}

The surface properties of comb-shaped polymers with perfluorooctyl ethyl side-chains are strongly related to the ordered structure of the side-chains at the surface. In this work, the thermal behavior, liquid-crystalline structure, and functional group orientation of comb-shaped polymers containing perfluorooctyl side-chains with poly(acrylate) (PFA-C8) and poly(vinyl ether) (PFAVE8) backbones are discussed based on DSC, synchrotron-source X-ray diffraction, and FTIR measurements. Despite the similar tilted hexatic smectic structures and packing entropies, the isotropization temperature, Ti, of the PFA-C8 is significantly higher than the PFAVE8. Detailed characterization of the conformation, alignment, and organization of the perfluorooctyl side-chains indicate that the difference in Ti is related to the configuration of side-chains and interactions between the carbonyl groups along the acrylate backbone. The present findings show that the type of the linkage between the polymer backbone and fluorinated side-chain mesogens affects the conformation and plays an important role in determining thermal behavior.

Quantitative phase analysis of bauxites and their dissolution products

Quantitative phase analysis for four bauxite samples sourced from different geological regions was conducted with Rietveld refinement of synchrotron sourced X-ray diffraction (XRD) data. Minor and trace phases were concentrated using (i) caustic leaching to selectively remove phases such as gibbsite, boehmite and kaolinite and (ii) dithionite–citrate–bicarbonate leaching to selectively remove the iron oxide phases such as goethite and hematite, and reanalysed. Bauxites are normally recognised as very difficult samples for quantitative phase analysis (QPA). The use of synchrotron XRD in this paper allowed characterisation with QPA, crystallite size determination and elemental substitution in some phases. Elemental composition analysis by X-ray fluorescence demonstrated close agreement with the diffraction data and allowed an estimate of the composition of the non-crystalline component of the bauxite samples. Other characterisation techniques used include thermogravimetric/differential scanning calorimetry to determine the phase transitions and mass loss, and transmission electron microscopy/energy dispersive spectroscopy to capture the morphology of the crystallites in the bauxite samples.

Nanoscale co-precipitation and mechanical properties of a high-strength low-carbon steel

Nanoscale co-precipitation in a novel high-strength low-carbon steel is studied in detail after isothermal aging. Atom-probe tomography is utilized to quantify the co-precipitation of co-located Cu precipitates and M 2C (M is any combination of Cr, Mo, Fe, or Ti) carbide strengthening precipitates. Coarsening of Cu precipitates is offset by the nucleation and growth of M 2C carbide precipitate, resulting in the maintenance of a yield strength of 1047 ± 7 MPa (152 ± 1 ksi) for as long as 320 h of aging time at 450 °C. Impact energies of 153 J (113 ± 6 ft-lb) and 144 J (106 ± 2 ft-lb) are measured at −30 °C and −60 °C, respectively. The co-location of Cu and M 2C carbide precipitates results in non-stationary-state coarsening of the Cu precipitates. Synchrotron-source X-ray diffraction studies reveal that the measured 33% increase in impact toughness after aging for 80 h at 450 °C is due to dissolution of cementite, Fe 3C, which is the source of carbon for the nucleation and growth of M 2C carbide precipitates. Less than 1 vol.% austenite is observed for aging treatments at temperatures less than 600 °C, suggesting that transformation-induced plasticity does not play a significant role in the toughness of specimens aged at temperatures less than 600 °C. Aging treatments at temperatures greater than 600 °C produce more austenite, in the range 2–7%, but at the expense of yield strength.

Exclusive Endo-Cavity Interplay of t-Bu-calix[6]arene with C70

Toluene solutions of fullerene C70 and t-Bu-calix[6]arene form a 2:1 inclusion complex that has been structurally authenticated using synchrotron source X-ray diffraction data. Remarkably, the fullerene is not included in the cavity of the calixarene, and this has implications in predicting the structures of fullerene complexes of other calixarenes and container molecules. The fullerenes shroud the exo surface of the calixarene at the van der Waals limit, with the fullerenes arranged into corrugated sheets, with each calixarene interdigitated at the upper rim with the upper rim of two other calixarenes, the macrocycles forming a bilayer separating the sheets of fullerenes.

Conformational Conversion and Local Packing of Cyclic Olefin Copolymers

Cyclic olefin copolymer (COC, poly(norbornene-co-ethylene)) catalyzed by ansa-ethylenebis(indenyl)zirconium dichloride (Et[Ind]2ZrCl2)/methylaluminoxane (MAO) gives rise to phenomenal increase of Tg upon annealing. Unaveraged solid-state 13C NMR resonance of the CH carbons in the norbornene (53 and 49 ppm) evidenced the conformation conversion from T[X]T and G[X]G to more stable T[X]G conformers (where [X] = [T] or [G] represent the norbornene chain conformation). As the persistent length increases with the conversion, local packing of the rigid chain subsequently occurs. Synchrotron source X-ray diffraction provides clear evidence of the averaged interchain contraction from 12.0 to 8.5 Å and a tighter distribution in the spacing after annealing. In the preannealed state, T1pH relaxation time revealed both mobile (where conformer converts) and rigid components (where conformation is frozen), which coalesce into a further rigid component after extended annealing. The mechanisms governing the packing in amorphous COC are likely by the random chain diffusion and not from cooperative motion as described by the bundle-packing model.

Crystallographic preferred orientation in albite samples deformed experimentally by dislocation and solution precipitation creep

The crystallographic preferred orientations of a series of experimentally deformed fine-grained albite aggregates were measured by synchrotron source X-ray diffraction. Most samples were deformed and extensively recrystallized by low-temperature recrystallization-accommodated dislocation creep. In axial compression as well as simple shear these samples developed weak but distinct crystallographic preferred orientations consistent with intracrystalline slip on {001}<100>; the sheared samples have a marked asymmetry of the <100> maxima with respect to the shear zone boundaries. One sample was axially compressed by solution precipitation creep; it developed a somewhat different but equally strong preferred orientation, perhaps reflecting crystallographic anisotropy in rates of dissolution and growth.

Synthesis of Superlattices of Intercalated Transition Metal Dichalcogenides

Thin films of oriented Fe and Cr intercalated (NbSe2)x(TiSe2)y superlattices have been synthesized by controlled annealing of elementally modulated reactants. Analytic techniques have been developed to extract the average c-axis structure of the unit cell, the distribution of c-axis crystal sizes, and the distribution of structural defects from X-ray diffraction data. High-resolution synchrotron source X-ray diffraction data were collected from a [(Fe0.33NbSe2)8(Fe0.33TiSe2)8]12 sample (i.e., 12 superlattice unit cells in the film, each cell containing 8 layers of Fe0.33NbSe2 followed by 8 layers of Fe0.33TiSe2) at three anomalously scattering wavelengths. Analysis determined structural parameters within 2% of published values for the parent compounds, typical crystal sizes of 200−500 A, and typical coherence losses over a unit cell of ±1%. Theoretical diffraction profiles calculated directly from the model structure are shown to agree satisfactorily with experiment. The flexibility offered by our growth ...