Morphology of polyanhydride copolymers: Time‐resolved small‐angle X‐ray scattering studies of crystallization

Synchrotron small‐angle X‐ray scattering (SAXS) was used to study the isothermal crystallization kinetics of a family of polyanhydride copolymers consisting of 1,6‐bis(p‐carboxyphenoxy)hexane and sebacic acid monomers. In situ SAXS experiments permitted the direct observation of the crystallization kinetics. The structural parameters (the long period, lamellar thickness, and degree of crystallinity) were obtained from Lorentz‐corrected intensity profiles, one‐dimensional correlation functions, and interface distribution functions to form a comprehensive picture of the crystal morphology. The combination of these three analyses provided information not only on the lamellar dimensions but also on the polydispersity (nonuniformity) of these dimensions. Where possible, the crystallization kinetics were interpreted with a modified version of the Avrami equation. The results can be used to perform the rational design of controlled‐drug‐release formulations because crystallinity affects drug‐release kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 463–477, 2005     

2.1 Anorganische industrielle Produkte

Ohne Zusammenfassung     

Zur Sicherheit beim Druckaufschluß im Teflongefäß

Analytical and Bioanalytical Chemistry -     

Investigations of hydrogen-bonded systems: Local density approximation and gradient corrections

The applicability of the local density approximation (LDA ) and of corresponding gradient corrections (for the exchange and correlation energy) for the treatment of the hydrogen bond is investigated. As test systems, we consider the water dimer and the H₂O…?HX complexes (X = F, Cl, Br): Using an LCAO scheme, their equilibrium geometries and interaction energies are ?alculated and compared with experimental data and with other calculations. We obtain that the LDA gives the geometries in qualitative agreement with other data, whereas the energies are overestimated. The use of the gradient corrections (GC ) according to Becke and Perdew leads to a significant improvement of the geometry, and especially of the interaction energies. The calculations indicate further that LDA + GC should also be able to describe weaker intermolecular interactions than the usual hydrogen bond. Finally, a short discussion of the charge distribution and the dipole moments of the H₂O…?HX complexes is performed. © 1994 John Wiley & Sons, Inc.     

High-resolution imaging of inhomogeneities in superconducting tunnel junctions by scanning with a modulated electron beam

A two-dimensional image of spatial structures within a superconducting tunnel junction can be obtained by scanning the current-biased junction with an electron beam and detecting the voltage change. The resolution of this imaging technique is governed by the thermal-healing length which describes the spatial diffusion of the beam energy through the superconducting film. Due to the thermal skin efect this resolution can be improved remarkably by high-freqency modulation of the beam intensity and synchronous signal detection.     

2. Spezielle produkte und Anwendungsgebiete

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Strukturelle und magnetische Untersuchungen an Hexachlorowolframaten(V)

Structural and Magnetic Investigations of Hexachlorotungstates(V) CsWCl₆ crystallizes in the monoclinic space group C2/c with the lattice dimensions a = 12.097(8), b = 6.327(5), c = 15.30(1) Å, β = 128.4(1)° and 4 formula units. The compounds AWCl₆ (A = Rb, K, NH₄) are isotypic with CsWCl₆ as shown by powder patterns. Single-crystal photographs of [N(C₂H₅)₄]WCl₆ show monoclinic symmetry, space group P2₁/n with a = 11.737(8), b = 10.239(7), c = 7.191(5), β = 101.46(8)° and Z = 2. Both structures are composed of scarcely deformed WCl₆ octahedra. The trigonal compression of the octahedra results in a slightly negative deformation parameter according to the Figgis-model of the magnetic behaviour of d¹-systems. Above 80 K the μ² vs. T-curve is linear. This leads to a spin-orbit coupling constant of 1250 ± 200 cm^?1 and a covalence parameter of 0.6–0.8. Comparing the spectra of WCl₆, CsWCl₆ and Cs₂WCl₆ the beginning of the charge-transfer region was determined. The crystal field strength for CsWCl₆ was found as Δ = 16 000 cm^?1.