Catastrophic phase inversion in region II of an ionomeric polymer-water system

Previous work has identified distinct regions, on a phase inversion map, for dispersions of polyurethane ionomer (PUI) and water. In this study, events that occur, before, during, and after catastrophic phase inversion (provoked by adding water to polyurethane ionomer (PUI) in the RII regions of the phase inversion map) have been studied in order to characterise the inversion mechanism. Before phase inversion, initial water addition leads to the hydration of ionic groups and eventually water drops start to form in the hydrophobic portions of the polymer matrix. At the phase inversion point, the PUI-water interface restructures and the ionomer disintegrates into a dispersion of spherical particles enclosed by a continuous aqueous phase. It is suggested that pseudo-drop structures are formed simultaneously during the production of the small polymer-in-water drops. After phase inversion, water addition dilutes the emulsion and destroys the apparent ionic-centre-rich environment surrounding any isolated ionic groups on a particle surface. The larger water-in-polymer drops are likely to have participated in the phase inversion and the smaller water drops form the primary water drops in the multiple emulsions. The resultant emulsions are stable over a period of a few months but very few multiple drops remain after 1(1/4) years.     

Graphite furnace atomic absorption spectrometric determination of ruthenium in iron meteorites

A procedure for the determination of ruthenium in iron meteorites involves its oxidation to RuO₄ by sodium periodate in hydrochloric acid and extraction of the tetroxide into chloroform. Various parameters of the method were studied: sample dissolution, optimum amount of oxidant, shaking time, distribution ratio and stability of the complex. The relative standard deviation assessed from replicate analyses of the North Chile iron meteorite was 6.6%. There are no certified standards for iron meteorites, but the value of 20.0 μg g^? obtained for this meteorite compares well with a reported abundance of 19.3 μg g^?1 obtained by radiometric neutron-activation analysis (RNAA). The analysis of 15 meteorites that had previously been analysed by RNAA gave values averaging 11% below those reported by the latter method, but within the standard deviation of the RNAA data. It is considered that the present method is a more practical alternative to RNAA for the determination of ruthenium in iron meteorites.     

Rapid method for the determination of alachlor, atrazine and metolachlor in groundwater by solid-phase extraction

A solid-phase extraction method is described for the separation of alachlor, atrazine and metolachlor from groundwater using solid-phase disposable columns. The method is rapid, reproducible and uses considerably fewer reagents than classical liquid-liquid methods. The average recoveries were greater than 90% for all three compounds.     

Ca(2.5)Sr(0.5)GaMn2O8: diamagnetic Ga in control of the structural and electronic properties of a bilayered manganate

The temperature dependence of the crystal structure and electronic properties of brownmillerite-like Ca(2.5)Sr(0.5)GaMn(2)O(8) has been studied by neutron powder diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO(6) octahedra approximately 50 K above the 3D Néel temperature of approximately 150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO(4) layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn(3+) and Mn(4+) cations in a 1:1 ratio, and the behavior in the region of the Néel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO(4) tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers.     

Interfacial and intrafacial linkage isomerizations of rhenium complexes with aromatic molecules

The mechanisms for the interconversion of facial diastereomers of a variety of TpRe(CO)(L)(eta(2)-L(Ar)) complexes [L = (t)BuNC, pyridine (py), PMe(3), or 1-methylimidazole (MeIm); L(Ar) = benzene, anisole, naphthalene, 1-methylpyrrole, furan, or thiophene; Tp = hydridotris(pyrazolyl)borate] have been investigated by (1)H NMR spin saturation experiments. In addition, the rates and free energies of activation for these processes were calculated from spin saturation experiments and T(1) measurements. The operative mechanisms for interconversion of the pi diastereomers were found to be nondissociative, undergoing either an interfacial or intrafacial linkage isomerization. A comparison of the kinetic parameters for isomerization of related eta(2)-olefin complexes of the [TpRe(CO)(PMe(3))] and [CpRe(NO)(PPh(3))](+) fragments is also presented.     

The extraction of elements with cyclic solvents and its application to geochemical analysis

The extraction of the elements Zn, Cd, Hg, Ga, In, Tl, Sn, Pb, As, Sb and Bi into the solvents cyclohexanone, cyclohexanol, and cyclohexane from hydrochloric acid solutions, has been studied. Cyclohexanone is a more efficient but less selective extracting agent than cyclohexanol while cyclohexane has little extracting power. Solvent extraction of hydrochloric acid solutions of materials of geochemical interest into cyclohexanone has been used to enrich trace elements prior to spectrochemical analysis.     

Harmonic analysis of large systems. I. Methodology

Methods have been developed for the determination of vibrational frequencies and normal modes of large systems in the full conformational space (including all degrees of freedom) and in a reduced conformational space (reducing the number of degrees of freedom). The computational method, which includes Hessian generation and storage, full and iterative diagonalization techniques, and the refinement of the results, is presented. A method is given for the quasiharmonic analysis and the reduced basis quasiharmonic analysis. The underlying principle is that from the atomic fluctuations, an effective harmonic force field can be determined relative to the dynamic average structure. Normal mode analysis tools can be used to characterize quasiharmonic modes of vibration. These correspond to conventional normal modes except that anharmonic effects are included. Numerous techniques for the analyses of vibrational frequencies and normal modes are described. Criteria for the analysis of the similarity of low-frequency normal modes is presented. The approach to determining the natural frequencies and normal modes of vibration described here is general and applicable to any large system. © 1995 John Wiley & Sons, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America.