title: Coaggregation of Two Anionic Azo Dyestuffs: A Combined Static Light Scattering and Small-Angle X-ray Scattering Study.
abstract: The formation of azo dyestuff aggregates in dilute aqueous solution induced by the addition of Mg2+, Ca2+, Sr2+, or Ba2+ions is followed by time-resolved static light scattering (SLS) and time-resolved small-angle X-ray scattering (SAXS). Time-dependent molar mass data of the growing aggregates is interpreted by means of a kinetic model introduced by Lomakin et al. ( Proc. Natl. Acad. Sci. U.S.A. 1996 , 93 , 1125 ) for the description of β-amyloid aggregation. This interpretation reveals significant trends within the homologous series of alkaline earth cations. The trends refer to the nucleation and the growth rate of the dyestuff fibers. Time-resolved SAXS experiments indicate that these first two stages are followed by a third one during which a network forms by partial lateral alignment of fibers. At high enough dyestuff concentrations, this network formation even leads to a gel-like phase. Anomalous SAXS (ASAXS) on such a gel phase formed upon the addition of Sr2+revealed the extent of neutralization of the dyestuff molecules within the gel by the specifically interacting alkaline earth cations.
authors.affiliation: Physikalische Chemie, Universität Paderborn , Warburger Straße 100, D-33098 Paderborn, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Michels
authors.affiliation: Institut Weiche Materie und Funktionale Materialien, Helmholtz-Zentrum Berlin , Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Goerigk
authors.affiliation: Deutsches Elektronen-Synchrotron , Notkestraße 85, D-22607 Hamburg, Germany.
authors.forename: Ulla
authors.initials: U
authors.lastname: Vainio
authors.affiliation: Procter & Gamble Technical Centre , Whitley Road, Longbenton, Newcastle Upon Tyne, Tyne And Wear, NE12 9SR, United Kingdom.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Gummel
authors.affiliation: Physikalische Chemie, Universität Paderborn , Warburger Straße 100, D-33098 Paderborn, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Huber