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Ordering of Ionic Solutes in Dilute Solutions through Attraction of Similarly Charged Solutes—A Change of Paradigm in Colloid and Polymer Chemistry
Author(s) -
Ise Norio
Publication year - 1986
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.198603231
Subject(s) - counterion , dispersity , chemistry , colloid , ionic bonding , aqueous solution , chemical physics , polymer , ion , extended x ray absorption fine structure , small angle x ray scattering , scattering , thermodynamics , polymer chemistry , absorption spectroscopy , physics , organic chemistry , optics
EXAFS measurements indicate the presence of a quasi lattice‐like ordering of simple ions in dilute solutions. Small‐angle X‐ray scattering (SAXS) measurements on dilute aqueous solutions of synthetic macroions, polynucleotides, and proteins show a single broad peak; a binary mixture of synthetic macroions of different molecular weight gives a new scattering curve that is entirely different from the composite curve of the constituents before mixing. This would indicate that the macroions are distributed in a fairly regular way in the solution. The intermacroion spacing (2 D exp ) obtained by the Bragg equation is found to be smaller than the average spacing (2 D 0 ) calculated from the polymer concentration. Furthermore, the 2 D exp value decreases with increasing number of charges per macroion. This finding is confirmed by studies on model systems, e. g. on monodisperse ionic latex particles, which are large enough (diameter: about 3000 Å) to be seen under the ultramicroscope. It follows, from the inequality relation 2 D exp <2 D 0 , that there is an attraction between ionic species of like‐charge. This conclusion contradicts prevailing views in colloid chemistry; it has been pointed out that such a behavior can be explained in terms of a new theory, in which counterions between the macroions or ionic latex particles play a decisive role.