Effects of mono- and divalent cations on the structure and thermodynamic properties of polyelectrolyte gels

Matan Mussel, Peter J. Basser, Ferenc Horkay

Research output: Contribution to journalArticlepeer-review


Measurements are reported on the effect of monovalent and divalent salts on the swelling behavior and supramolecular structure of sodium polyacrylate gels (NaPA) made by osmotic swelling pressure and small angle neutron scattering measurements. The swelling response of the gels in solutions of ten different monovalent salts is found to be practically identical indicating that the principal effect of monovalent ions is screening the electrostatic repulsion among the charged groups on the polyelectrolyte chains; i.e., chemical differences between the monovalent ions do not play a significant role. Introducing Ca2+ ions into the equilibrium NaCl solution results in a sharp volume transition of the gels. The threshold Ca2+ ion concentration at which the transition occurs increases with increasing NaCl concentration in the surrounding bath. It is demonstrated that the swelling behavior of NaPA gels exhibits universal properties in solutions containing both NaCl and CaCl2. Osmotic swelling pressure measurements reveal that both the second and third virial coefficients decrease with increasing CaCl2 concentration until the volume transition is reached. The macroscopic measurements are complemented by small angle neutron scattering that reveals the variation of the thermodynamic length scales as the volume transition is approached. The thermodynamic correlation length L increases with increasing CaCl2 concentration.

Original languageEnglish
Pages (from-to)4153-4161
Number of pages9
JournalSoft Matter
Issue number20
StatePublished - 2019
Externally publishedYes

Bibliographical note

Funding Information:
This research was supported by the Intramural Research Program of the NICHD, NIH. We acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the neutron research facilities used in this work. This work utilized facilities supported in part by the National Science Foundation under Agreement No. DMR-0944772. We gratefully acknowledge the help and consultation of Drs Jack Douglas and Boualem Hammouda (NIST).

Publisher Copyright:
© 2019 The Royal Society of Chemistry.

ASJC Scopus subject areas

  • Chemistry (all)
  • Condensed Matter Physics


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