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 journalArticle

Abstract

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
Volume16
Issue number31
DOIs
Publication statusPublished - Aug 21 2020

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics

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