2 research outputs found
SAXS and ASAXS on Dilute Sodium Polyacrylate Chains Decorated with Lead Ions
Bivalent lead ions as representative
main group heavy metal cations
form specific interactions with the negatively charged COO<sup>–</sup> residues of sodium polyacrylate chains in dilute aqueous solution.
The interactions eventually lead to aggregation and precipitation
of sodium polyacrylate chains partially neutralized with Pb<sup>2+</sup> cations. The present work outlines a small-angle X-ray (SAXS) and
light scattering study of the polyacrylate chains undergoing changes
in coil conformation and successive aggregation while approaching
and crossing the Pb<sup>2+</sup>-induced precipitation threshold.
The study reveals a coil shrinking while approaching the precipitation
threshold. Anomalous SAXS (ASAXS) complemented this information with
a first insight into the spatial distribution of the Pb<sup>2+</sup> cations captured by the polyacrylate chains together with a semiquantitative
estimation of the amount of Pb<sup>2+</sup> cations located within
the collapsed domains of the shrinking chains. Conformational aspects
of the shrinking coils could be established by means of model form
factors of hybrid chains formed by a freely jointed chain of rods
with spheres located on all or part of the joints. Development and
application of the form factors of the pearl-necklace-like hybrid
model chains and the use of quantitative analysis of ASAXS data are
described and discussed in detail
Coaggregation of Two Anionic Azo Dyestuffs: A Combined Static Light Scattering and Small-Angle X‑ray Scattering Study
The
formation of azo dyestuff aggregates in dilute aqueous solution
induced by the addition of Mg<sup>2+</sup>, Ca<sup>2+</sup>, Sr<sup>2+</sup>, or Ba<sup>2+</sup> 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 Sr<sup>2+</sup> revealed the extent of neutralization
of the dyestuff molecules within the gel by the specifically interacting
alkaline earth cations