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  • 1
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Three techniques for analyzing rare earth elements (REE) in geological materials are described, i.e. instrumental neutron activation analysis (INAA), neutron activation analysis with pre-irradiation chemical REE separation (PCS-NAA) and radiochemical neutron activation analysis (RNAA). The knowledge of REE concentrations in eclogites, peridotites and minerals from the earth's lower crust and upper mantle is very useful in constraining their petrogenetic history.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0392-6737
    Keywords: Disperse systems ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The phase diagram of the ternary system,i.e. poly(diallyldimethylammonium chloride), poly(acrylic acid, sodium salt), and water was investigated by varying the molecular weight of the components. In general, a range of phase separation is surrounded by a one-phase system. The range of phase separation can be subdivided into a region of flocculation and/or coacervation in contrast to stable symplex dispersions. By increasing the molecular weight of the components the range of phase separation is increased and phenomena of flocculation followed by coacervation were observed predominantly. Above a molecular weight of 10 000 g/mol the transition to concentrated macroscopic homogeneous one-phase systems was observed at a constant ionic strength of 2 mol/l coinciding with the «critical ionic strength» for Coulombic interactions in this system. That means the transition to concentrated one-phase systems can be understood by the disappearance of Coulombic forces above a system-specific ionic strength resulting in a quite additive behaviour of the mixtures with regard to the components.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of Aryl-bis(trimethylsilyl)-phosphonic Acid Esters via Tris-trimethylsilylphosphite - a Contribution of the Nickel-catalyzed Michaelis-Arbusov Reaction.The preparation of various aryl-bis(trimethylsilyl)-phosphonic acid esters via P(OSiMe3)3 or a mixture of HP(O)(OSiMe3)2/P(OSiMe3)3/Me3Si—NH—SiMe3 in presence of nickel compounds are described. The structures are proved by the 31P n.m.r. spectra.
    Notes: Es wird die nickel-katalysierte Darstellung verschieden-substituierter Aryl-bis(trimethylsilyl)-phosphonsäureester via Tris-trimethylsilylphosphit bzw. eines Gemisches von Bis-/Tris-trimethylsilylphosphit/Hexamethyldisilazan beschrieben. Ihre 31P-NMR-Daten werden mitgeteilt.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1435-1536
    Keywords: Polyelectrolyte complexes ; ampholytes ; surface charge ; electrophoresis ; viscometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Isotachophoresis and viscometric measurements were performed on aqueous dispersions of non-stoichiometric polyelectrolyte complexes in order to elucidate the surface charge situation of the complex particles in dependence on component charge density, ratio of cationic to anionic groups in the complex, and pH and ionic strengths of the ambient medium. Components for complex formation were acryl-based anionic and cationic polyelectrolytes of the pendent type. From our results, an amphoteric character of the polyelectrolyte complex particles can be concluded, with an isoelectric point characterized by zero mobility and a minimum in reduced viscosityη spec/c of the particle dispersion, and with the sign of net surface charge depending on ambient pH and component charge density. The influence of ionic strength on theη spec/c vs pH plots can be interpreted by assuming a competition between salting-out and electrostatic shielding effects. No correlation could be established between the overall molar ratio of cationic to anionic groups and the isoelectric point of the complex particles, which obviously indicates a different composition of “surface” and “bulk” of the polyelectrolyte complex particles.
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  • 5
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Carboxymethyl cellulose and C-6-carboxy cellulose were treated with SO3 and HSO3CL in DMF yielding the corresponding watersoluble sulfate half-esters. A preferred sulfation of primary hydroxyl groups was found by 13C-n. m.r. spectroscopy. The potentiometric titration of the polyelectrolytes showed significant differences in the titration behaviour which can be explained by the different acidity of the carboxy groups in the two cellulose derivatives.
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  • 6
    ISSN: 1435-1536
    Keywords: Key words Polyelectrolytes ; Lamellar liquid crystals ; Vesicle formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The object of the research was to investigate the influence of a semiflexible polyanion (carboxymethylcellulose) in the absence and presence of a more flexible cationic polyelectrolyte [poly(diallyldimethyl-ammonium chloride)] on structure formation in liquid-crystalline model systems consisting of sodium dodecyl sulfate (SDS)/ decanol/water. Small-angle X-ray measurements in combination with electron microscopic investigations show the adsorption of the polycation on the SDS head groups. These polymer-modified lamellae form multilamellar vesicles. The semiflexible polyanion was embedded into the liquid crystal without macroscopic phase separation and multivesicular vesicles were formed on the supramolecular level. In combination the oppositely charged polyelectrolytes induce the formation of multivesicular structures where two lamellar structures coexist.
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  • 7
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In continuation of our work on the structure of polyanion-polycation-complexes as a function of molecular parameters of the individual polyelectrolytes, the influence of the backbone chain hydrophobicity of polyanions with COOH groups at the end of the side chains on the complex formation has been investigated. As the cationic component were used quaternary polyammonium salts of various charge densities and degrees of branching. A cationic surfactant with C12 alkyl chain with a terminal quaternary ammonium group was included for comparison. The results indicate a weakening of the coulombic interactions with increasing hydrophobicity of the backbone of the polyanion.
    Notes: Im Rahmen unserer Arbeiten zur Bildungsweise und Struktur von Polyanion-Polykation-Komplexen in Abhängigkeit von molekularen Parametern der Ausgangskomponenten wurde der Einfluß der Hydrophobie der Rückgratkette regelmäßig verzweigter Polyanionen mit endständigen COOH-Gruppen an den Seitenketten auf die Komplexbildung untersucht. Als kationische Komponente dienten quaternäre Polyammoniumsalze unterschiedlicher Ladungsdichte und unterschiedlichen Verzwigungsgrades, sowie ein Kationtensid mit C12-Alkylkette und endständiger quaternärer Ammoniumgruppe. Die Ergebnisse sprechen für eine Schwächung der coulombschen Wechselwirkung mit wachsender Hydrophobie der Rückgratkette des Polyanions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The transition range between macroscopic soluble polycation-polyanion-complexes (symplexes) and polysalt precipitates was investigated by combining potentiometry, conductometry and tubidimetry. As starting materials mainly poly(ethylene imine) and cellulose sulphate as well as cationically and anionically modified poly(acrylamide)s were used. Under the conditions applied, only in a few systems the formation of stoichiometric 1: 1-symplexes is indicated by the electrochemical or the turbidimetric endpoint. The course of phase separation depends principally on the structure of the polyelectrolytes, but it is also strongly affected by the choice of the excess component and the contact of the low-molecular electrolyte (NaCl).
    Notes: Der Übergang von makroskopisch löslichen Polyanion-Polykation-Komplex (Symplex) zur Polysalzfällung wird mittels Kombination von Potentiometrie, Konduktometrie und Turbidimetrie untersucht. Als Ausgangsmaterialien dienen vor allem Cellulosesulfat und Polyethylenimin sowie anionisch und kationisch modifizierte Polyacrylamide. Unter den angewandten Bedingungen wurden bei elektrochemischer bzw. bei turbidimetrischer Endpunktanzeige nur in wenigen Fällen 1: 1-Symplexe erhalten. Die Endpunkte und der Verlauf der Trübungskurve hängen von der chemischen Struktur der Komponenten, aber in erheblichem Maße auch vom Salzgehalt (NaCl) und von der Wahl der Überschußkomponente ab.
    Additional Material: 4 Ill.
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  • 9
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Comparing a C-6-substituted carboxy cellulose and carboxy methyl cellulose samples differing in substituent distribution, the acidity of the COOH-group and the symplex formation of these polymers are investigated. The acidity of the COOH-group is inversely correlated to the average distance between the anionic charge centre and the anhydroglucose ring. Obviously, no significant effect of the regioselectivity of substitution on symplex formation exists.
    Notes: Es wird über vergleichende Untersuchungen zur Acidität der Carboxygruppe und zur Symplexbildung bei einer C-6-substituierten Carboxycellulose einerseits, Carboxymethylcellulosen mit unterschiedlicher Substituentenverteilung andererseits berichtet. Die Acidität der Carboxygruppe korreliert invers zum mittleren Abstand zwischen anionischem Ladungszentrum und Anhydroglucosering. Ein signifikanter Einfluß der Regioselektivität der Substitution auf die Symplexbildung besteht offensichtlich nicht.
    Additional Material: 6 Ill.
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