Screening lengths and osmotic compressibility of flexible polyelectrolytes in excess salt solutions

Carlos G. Lopez, Ferenc Horkay, Matan Mussel, Ronald L. Jones, Walter Richtering

Research output: Contribution to journalArticlepeer-review


We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length (ξ) and osmotic compressibility are measured as a function of polymer (c) and added salt (cS) concentrations, and the results are compared with scaling predictions and the random-phase approximation (RPA). In Dobrynin et al.'s scaling model the osmotic pressure consists of a counter-ion contribution and a polymer contribution. The polymer contribution is found to be two orders of magnitude smaller than expected from the scaling model, in agreement with earlier observations made on neutral polymers in good solvent condition. RPA allows the determination of single-chain dimensions in semidilute solutions at high polymer and added salt concentrations, but fails for cS ≤ 2 M. The χ parameter can be modelled as the sum of an intrinsic contribution (χ0) and an electrostatic term: χ ∼ χ0 + K′/√cS, where χ0 > 0.5 is consistent with the hydrophobic nature of the backbone of NaPSS. The dependence of χelec ∼ 1/√cS disagrees with the random-phase approximation (χelec ∼ 1/cs), but agrees with the light scattering results in dilute solution and Dobrynin et al.'s scaling treatment of electrostatic excluded volume.

Original languageEnglish
Pages (from-to)7289-7298
Number of pages10
JournalSoft Matter
Issue number31
StatePublished - 21 Aug 2020
Externally publishedYes

Bibliographical note

Funding Information:
F. H. and M. M. acknowledge the support of the Intramural Research Program of the NIH, NICHD. Access to the NGB 30 m SANS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under Agreement No. DMR-1508249. Use of the NGB 10 m SANS was supported by the NIST nSoft Consortium. We thank the ILL for beamtime. We thank Dr B. Hammouda for his excellent advice.

Publisher Copyright:
© The Royal Society of Chemistry.

ASJC Scopus subject areas

  • Chemistry (all)
  • Condensed Matter Physics


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