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Tuning the Collapse Transition of Weakly Charged Polymers by Ion-Specific Screening and Adsorption

preprint
submitted on 10.08.2018 and posted on 10.08.2018 by Richard Chudoba, Jan Heyda, Joachim Dzubiella
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 and shall be useful for further guidance of experiments.

Funding

DFG DZ-74/6; GAČR 16-24321Y

History

Email Address of Submitting Author

richard.chudoba@helmholtz-berlin.de

Institution

Helmholtz-Zentrum Berlin

Country

Germany

ORCID For Submitting Author

0000-0002-8064-0387

Declaration of Conflict of Interest

No conflict of interest.

Licence

Exports