A new strategy for the simultaneous modeling of molecular weight distribution (MWD) and degree of branching distribution (DBD) for such branched polymers as bimodal low-density polyethylene is presented, based on the Galerkin h-p finite element package PREDICI, a commercial code.The key problem of how to address a bidimensional distribution is successfully solved by using so-called reduced or pseudo distributions. The branching distribution per chain length is modeled by moment equations, thus yielding distributions of branching moments over chain length. No closure relationships are required. The MWD/DBD curves obtained are the most probable ones for the given reaction mechanisms and kinetic data. Simulated MWD and DBD curves are compared to experimental data from gel permeation chromatography and light scattering; the agreement found is good in general and excellent in one case. The bimodal MWD of the autoclave low-density polyethylene (ldPE) IUPAC Alpha could be reproduced well. It is finally shown that the shapes of MWD and DBD are highly sensitive, quantitative measures for random scission.
Poiseuille flow to measure the viscosity of particle model fluids.Backer, J.A.; Lowe, C.P.; Hoefsloot, H.C.J.; Iedema, P.D. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The most important property of a fluid is its viscosity, it determines the flow properties. If one simulates a fluid using a particle model, calculating the viscosity accurately is difficult because it is a collective property. In this article we describe a new method that has a better signal to noise ratio than existing methods. It is based on using periodic boundary conditions to simulate counter-flowing Poiseuille flows without the use of explicit boundaries. The viscosity is then related to the mean flow velocity of the two flows. We apply the method to two quite different systems. First, a simple generic fluid model, dissipative particle dynamics, for which accurate values of the viscosity are needed to characterize the model fluid. Second, the more realistic Lennard-Jones fluid. In both cases the values we calculated are consistent with previous work but, for a given simulation time, they are more accurate than those obtained with other methods.
An infrared spectroscopic study of the nature of zinc carboxylates in oil paintingsHermans, J.J.; Keune, K.; van Loon, A.; Iedema, P.D. Published in:Journal of analytical atomic spectrometry DOI:10.1039/c5ja00120jLink to publication Citation for published version (APA):Hermans, J. J., Keune, K., van Loon, A., & Iedema, P. D. (2015). An infrared spectroscopic study of the nature of zinc carboxylates in oil paintings. Journal of analytical atomic spectrometry, 30(7), 1600-1608. DOI: 10.1039/c5ja00120j General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 12 May 2018An infrared spectroscopic study of the nature of zinc carboxylates in oil paintings † Joen J. Hermans, * Katrien Keune, Annelies van Loon and Piet D. IedemaThe formation of metal soaps is a major problem for oil paintings conservators. The complexes of either lead or zinc and fatty acids are the product of reactions between common pigments and the oil binder, and they are associated with many types of degradation that affect the appearance and stability of oil paint layers.Fourier transform infrared spectroscopy (FTIR) reveals that a paint sample from The Woodcutter (after Millet) by Vincent van Gogh contains two distinct zinc carboxylate species, one similar to crystalline zinc palmitate and one that is characterized by a broadened asymmetric stretch COO À band shifted to 1570-1590 cm À1 . This observation has been made in many paintings. Although several hypotheses exist to explain the shifted broad carboxylate band, these were not supported by experimental evidence. In this paper, experiments were carried out to characterize the second zinc carboxylate type. It is shown that neither variations in the composition of zinc soaps (i.e. zinc soaps containing mixtures of fatty acids or metals) nor fatty acids adsorbed on pigment surfaces are responsible for the second zinc carboxylate species. X-Ray diffraction (XRD) and FTIR analysis indicate that the broad COO À band represents amorphous zinc carboxylates. These species can be interpreted as either non-crystalline zinc soaps or zinc ions bound to carboxylate moieties on the polymerized oil network, a system similar to ionomers.These findings uncover an intermediate stage of metal soap-related degradation of oil paintings, and lead the way to impr...
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