Search

Structural characteristics of optical quality poly(2-methoxy-5-(2‘-ethylhexyloxy)-1,4-phenylenevinylene) (MEH−PPV) films drop-cast from toluene solutions have been examined by use of wide-angle (WAXS) and small-angle X-ray scattering (SAXS) as well as field-emission scanning electron microscopy. For the as-cast film SAXS and WAXS patterns clearly suggest existence of nanodomains of mesomorphic order. Under grazing incidence, both SAXS and WAXS patterns of the as-cast film exhibit impressive uniaxial symmetry with strong scattering along the film normal; however, the corresponding normal-incidence patterns are circularly isotropic, implying in-plane random orientation. A structural model consisting of preferentially uniaxial-oriented nanodomains and disordered matrix is therefore proposed for the as-cast film. Annealing at 210 °C results in disorientation of nanodomains:  this decrease in structural asymmetry upon heat treatment correlates well with concomitant changes in charge transport behavior determined from time-of-flight measurements, manifesting dramatically decreased charge mobility as well as transition from nondispersive to dispersive modes.

We have successfully prepared a new class of self-assembled biomaterial:  a polypeptide-block-polypseudorotaxane diblock copolymer. This diblock copolymer is comprised of an α-helical polypeptide rod, based on γ-benzyl-l-glutamate, and an originally coiled segment P(EO19-r-PO3); it forms inclusion complexes with α-cyclodextrins (α-CDs) to give crystalline polypseudorotaxanes. Formation of the polypseudorotaxane converts the conformation of P(EO19-r-PO3) from a flexible chain into a rodlike structure, which results in a novel block copolymer exhibiting a rod−rod conformation. Intrinsic interactions (e.g., the polypseudorotaxane's channel-type crystallization, the polypeptide's secondary structure, and microphase separation) within and between these rod−rod diblock copolymers contribute to their hierarchical self-assembly behavior, which we characterized using DSC, ¹H NMR spectroscopy, ¹³C CP/MAS NMR spectroscopy, WAXS, and SAXS. The data obtained from the WAXS and SAXS studies clearly indicate the formation of juxtaposed bilayer-like nanostructure featuring hexagonally packed PBLG stacks and channel-type polypseudorotaxane moieties.

In-situ X-ray absorption spectroscopic investigations have been carried out to examine the changes of the electronic transitions and local structure at the Mn, Co, and Ni K-edge for the LiNi1/3Co1/3Mn1/3O2 electrode during charging and discharging process in this study. It was found that only Ni atom in Li1-xNi1/3Co1/3Mn1/3O2 is electroactive from the evolution of the XANES spectra and the bond length variation of Ni−O. It was found that the redox pairs of Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺ exist and the oxidation states of Mn and Co remain as Mn^IV and Co^III, respectively, in Li1-xNi1/3Co1/3Mn1/3O2 upon charge and discharge. The oxygen, rather than the transition-metal ions (Ni, Co, and Mn), functions as electron donor at the end of charge. In addition, the irreversible capacity at the first cycle derives mainly from the appearance of inactive Ni, which is evidenced by the energy shift E − E0 of the absorption edge for the Ni absorber and the bond length change of the Ni−O. A decrease/increase of Debye−Waller factor of Ni−O contribution results from a decrease/increase of Jahn−Teller active Ni^III concentration during cycling. The trends of the variations for the bond length and Debye−Waller factor for the second shell Mn−M and Ni−M contributions are significant and similar, suggesting the short-range ordering between Ni^II and Mn^IV may take place in this compound.

Three series of palladium(II) complexes 1−3 derived from 1,3,4-oxadiazoles exhibiting mesogenic properties are prepared and characterized. It was found that the formation of mesophases was sensitive to the numbers of alkoxy side chains. The compounds 3 appended with twelve side chains exhibited columnar (Col) phases, however, all other compounds 1−3 appended with four or eight side chains formed crystalline phases. Some derivatives (n = 8, 10, 12) of the series 3 were in fact mesogenic at room temperature. Powder XRD data indicated that the formation of columnar mesophase varied from rectangular (Colr) to hexagonal arrangements (Colh) was observed as carbon chains length increases. The crystal and molecular structure of palladium(II) complex of 2,5-bis(3,4,5-trimethoxy phenyl)-1,3,4-oxadiazole (3; n = 1) was determined by means of X-ray structural analysis. It crystallizes in the monoclinic space group p21/n, with a = 8.7736 (3) Å, b = 19.1568 (6) Å, c = 15.7834 (5) Å, β = 100.106 (1)°, and Z = 2. The geometry at palladium center is perfectly square planar, and two trans-chlorine atoms are almost perpendicularly located to the molecular plane determined by four 1,3,4-oxadiazole rings. The fluorescent properties of these compounds were also examined. All λmax peaks of the absorption and photoluminescence spectra of compounds 4 and 6 occurred at ca. 303−312 nm and 358−391 nm, respectively; whereas the quantum yields of some compounds were relatively low.

A series of alkanethiols, n-decanethiol (C10SH), n-dodecanethiol (C12SH), n-tetradecanethiol (C14SH), n-hexadecanethiol (C16SH), and n-octadecanethiol (C18SH), were introduced to study the reactivity of the laser-prepared Cu nanoparticles. The colloidal solutions containing alkanethiols resulted in the disulfide (RSSR) formation. In particular, the colorless and the lathy crystals were generated from the C14SH, C16SH, and C18SH. The psuedo-one-dimensional lathlike structures were resolved by the X-ray crystallographic analysis. UV−vis, TEM, high-resolution XRD, and proton NMR were carried out to characterize the Cu nanoparticles and the disulfide products. XPS and XANES measurements were employed to identify the Cu identity, as well. The laser-prepared Cu particles were mainly +0 charge with the possible formation of a thin Cu2O layer on the copper surfaces. It was interpreted that the disulfides resulted from the Cu and/or Cu (core)/Cu2O (thin shell) particles.

A template synthetic method to prepare densely packed metal nanostructures in functionalized (MCM)‐41 and MCM‐48 is described. The intrachannel surface of host silica has been functionalized to carry positive charges for the accommodation of highly concentrated and negatively charged metal complexes. After reduction, Au and Pt nanowire bundles in MCM‐41 as well as Pd nanowire networks in MCM‐48 are formed. The Pt nanowire bundles in MCM‐41 are observed to grow along a preferred direction and stack along Pt {111} planes relative to the pore wall of the host. Furthermore, bimetallic AuPt alloy nanowire bundles in MCM‐41 have also been prepared and characterized.

Abstract: Various X-ray diffraction methods have been applied to study the compression behavior of gibbsite, Al(OH)3, in diamond cells at room temperature. A phase transformation was found to take place above 3 GPa where gibbsite started to convert to its high-pressure polymorph. The high-pressure (HP) phase is quenchable and coexists with gibbsite at the ambient conditions after being unloaded. This HP phase was identified as nordstrandite based on the diffraction patterns obtained at room pressure by angle dispersive and energy dispersive methods. On the basis of this structural interpretation, the bulk modulus of the two polymorphs, i.e., gibbsite and nordstrandite, could be determined as 85 ± 5 and 70 ± 5 GPa, respectively, by fitting a Birch-Murnaghan equation to the compression data, assuming their Ko′ as 4. Molar volume cross-over occurs at 2 GPa, above which the molar volume of nordstrandite is smaller than that of gibbsite. The differences in the molar volume and structure between the two polymorphs are not significant, which accounts for the irreversibility of the phase transition. In gibbsite, the axial compressibility behaves as c/c o > a/a o > b/b o. This is due to the fact that the dioctahedral sheets along the c-axis are held by the relatively weak hydrogen bonding, which results in the greater compressibility along this direction. In nord- strandite, the axial compressibility is b/b o > c/c o > a/a o, which can also be interpreted as resulting from the the existence of hydrogen bonds along the b-axis.

Synchrotron X-ray radiation was utilized to study the structural change of layer-structured LiNi0.6Co0.25Mn0.15O2during cycling. Unlike the LiNiO2or LiCoO2systems, there was no new H2 phase formed during the whole charge–discharge process. With Li-deintercalated from LiNi0.6Co0.25Mn0.15O2, a single-phase reaction prevailed. It was reveled that both the aand caxes varied with different Li contents in this material system. Besides, the volumetric change after the first charge was only 4%; which was much smaller compared with those of LiNiO2, LiCoO2, and LiMnO2electrode materials. As a result, a better structure stability was derived.