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Tuning the collapse transition of weakly charged polymers by ion-specific screening and adsorption

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Abstract

The experimentally observed swelling and collapse response of weakly charged polymers to the addition of specific salts displays quite convoluted behavior that is not easy to categorize. Here we use a minimalistic implicit-solvent/explicit-salt simulation model with a focus on ion-specific interactions between ions and a single weakly charged polyelectrolyte to qualitatively explain the observed effects. In particular, we demonstrate ion-specific screening and bridging effects cause collapse at low salt concentrations whereas the same strong ion-specific direct interactions drive re-entrant swelling at high concentrations. Consistently with experiments, a distinct salt concentration at which the salting-out power of anions inverts from the reverse to direct Hofmeister series is observed. At this so called isospheric point, the ion-specific effects vanish. Furthermore, with additional simplifying assumptions, an ion-specific mean-field model is developed for the collapse transition which quantitatively agrees with the simulations. Our work demonstrates the sensitivity of the structural behavior of charged polymers to the addition of specific salt beyond simple screening and shall be useful for further guidance of experiments.

Graphical abstract: Tuning the collapse transition of weakly charged polymers by ion-specific screening and adsorption

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Publication details

The article was received on 10 Aug 2018, accepted on 07 Nov 2018 and first published on 08 Nov 2018


Article type: Paper
DOI: 10.1039/C8SM01646A
Citation: Soft Matter, 2018, Advance Article
  • Open access: Creative Commons BY license
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    Tuning the collapse transition of weakly charged polymers by ion-specific screening and adsorption

    R. Chudoba, J. Heyda and J. Dzubiella, Soft Matter, 2018, Advance Article , DOI: 10.1039/C8SM01646A

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