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Manfred H. Wagner Heike Bastian Peter Hachmann Joachim Meissner Stefan Kurzbeck H. Münstedt F. Langouche 《Rheologica Acta》2000,39(2):97-109
By generalizing the Doi-Edwards model to the Molecular Stress Function theory of Wagner and Schaeffer, the extensional viscosities
of polyolefin melts in uniaxial, equibiaxial and planar constant strain-rate experiments starting from the isotropic state
can be described quantitatively. While the strain hardening of four linear polymer melts (two high-density polyethylenes,
a polystyrene and a polypropylene) can be accounted for by a tube diameter that decreases affinely with the average stretch,
the two long-chain-branched polymer melts considered (a low-density polyethylene and a long-chain branched polypropylene)
show enhanced strain hardening in extensional flows due to the presence of long-chain branches. This can be quantified by
a molecular stress function, the square of which is quadratic in the average stretch and which follows from the junction fluctuation
theory of Flory. The ultimate magnitude of the strain-hardening effect is governed by a maximum value of the molecular stress,
which is specific to the polymer melt considered and which is the only free non-linear parameter of the theory.
Received: 1 June 1999/Accepted: 24 November 1999 相似文献
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Elena Bermejo Rosa Carballo Alfonso Castieiras Ricardo Domnguez C. Maichle-Mssmer Joachim Strhle Douglas X. West 《Polyhedron》1999,18(27):m816-3702
Reaction of group 12 metal halides in ethanol with the thiosemicarbazones 2-acetylpyridine-4N-ethylthiosemicarbazone (H4EL) and 2-acetylpyridine-N-oxide-4N-ethylthiosemicarbazone (H4ELO) produced the compounds [M(H4EL)X2] and [M(H4ELO)X2] [M=Zn(II), Cd(II) or Hg(II), X=Cl, Br or I]. The ligands and complexes were characterized by elemental analysis and by IR and NMR (1H, 13C, 113Cd, 199Hg) spectroscopy, and the structures of H4ELO·H2O and the complexes [Cd(H4EL)I2]·2DMSO, [Hg(H4EL)Br2]–DMSO, [Zn(H4ELO)Cl2] and [Zn(H4ELO)Br2] were determined by X-ray diffraction. The metal centers in the complexes have coordination number five, H4EL and H4ELO behaving as neutral NNS- and ONS-tridentate ligands, respectively. The coordination polyhedra are close to tetragonal pyramids, the degree of distortion towards trigonal bipyramids was estimated by τ calculation. Against the pathogenic fungi Aspergillus niger and Paecilomyces variotii, the mercury complexes of H4ELO had activities that at some doses exceeded that of nystatin. 相似文献
1000.
Li5ReN4, a Lithium Nitridorhenate(VII) with Anti Fluorite Superstructure At 673 K Li3N reacts with Re powder under N2 to pale yellow, microcrystalline Li5ReN4. The structure determination is based on X‐ray powder data: Spacegroup Pmmn (No. 59), Z = 2, a = 6.719(1) Å, b = 6.627(1) Å, c = 4.893(1) Å. The compound crystallizes in an anti‐type of a fluorite superstructure. In comparison to the aristo‐type – CaF2 – in Li5ReN4 tetrahedral interstices of a ccp nitrogen partial structure are unoccupied. The distribution of these vacancies is related with its orthorhombic distortion. Under aspects of crystal chemistry the tetragonally crystallizing compounds Li6MN4 with M = Mo, W result by partially filling up such vacancies. 相似文献