Transitions from simple electrolyte to polyelectrolyte in a series of polyphosphates

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 484; pp. 153 - 163
• Main Authors: Maki, Hideshi, Ibaragi, Kie, Fujimoto, Yoshiaki, Nariai, Hiroyuki, Mizuhata, Minoru
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.11.2015
• Subjects: 23Na NMR; Charge density; Donnan model; Polyion; Polymerization degree; Two variable theory; Charge density; Polyion; Polymerization degree; 23Na NMR; Donnan model; Two variable theory
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2015.07.064

[Display omitted] •Dependence of polyelectrolyte effects on the number of ionic groups was revealed.•Polyelectrolyte effects increased non-monotonically with phosphate groups number.•These behaviors were observed not only electrochemical titration but also 23Na NMR. The dependence of polyelectrolyte characteristics on the number of phosphate groups in a series of polyphosphates was clarified by potentiometric titration and 23Na nuclear magnetic resonance using the Donnan model. Ca2+ ion binding to various polyphosphates was consistently inhibited as supporting electrolyte concentration increased. The electrostatic interactions between polyions and counterions, which is peculiar to polyelectrolytes, was enhanced by an increase in the number of phosphate groups. The polyelectrolyte characteristics increased non-monotonically with the number of phosphate groups that constituted the molecules, that is, (1) gradual emergence with three or four phosphate groups, (2) marked strengthening from four to eight phosphate groups, and (3) saturation with eight or more phosphate groups. The characteristics of polyelectrolyte molecules comprising eight or more phosphate groups were independent of the degree of polymerization. These interesting behaviors were observed to be closely similar using two quite different experimental techniques, electrochemical titration and nuclear magnetic resonance.