"Ordered" structure in ionic dilute solutions: dendrimers with univalent and bivalent counterions.

摘要: As an intermediate sample of ionic solutes between colloidal particles (macroions) and simple electrolyte ions, we made small-angle x-ray scattering (SAXS) measurements for aqueous solutions poly(amido amine) dendrimers three generations (G4, G7, G10). The SAXS curves univalent acid showed a single peak, as observed synthetic macroions. peak position was dependent on the dendrimer concentration but independent not only (degree protonation) also counterion species. effective charge density determined by conductivity found to be insensitive nearest neighbor interparticle distance 2D(exp) calculated from structure factor G7 G10 obviously smaller, though slightly, than average 2D(0) molecular weights concentrations dendrimers, implying that formed two-state structures attractive force. ultra-small-angle curve hydrochloric solution did show upturn, which indicates existence large scale structural inhomogeneities such localized ordered structures, probably due weak attraction hence less clear distinction disordered regions. For sulfuric solutions, peaks were observed. bivalent counterions more strongly associated with ions ones. resulting low number confirmed directly measurements. These observations confirm counterion-mediated does exist even point out frequently advanced claim potential is essentially repulsive while appears necessarily correct. It noted intensity in dictated both number, contrast macroionic or dispersions appeared important.