Re-entrant swelling and redissolution of polyelectrolytes arises from an increased electrostatic decay length at high salt concentrations

Liu G.;Parsons D.;Craig V. S. J.

2020-01-01

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Abstract

Hypothesis: A detailed understanding of the influence of electrolytes on the conformation of polyelectrolyte chains is an important goal made challenging by the strong coupling between electrostatic interactions and chain conformation. This challenge is particularly evident at moderate to high salt concentrations where mean-field theories of electrolytes are no longer applicable and are therefore unable to predict the interactions between neutral or like charged surfaces that leads to re-entrant swelling of DNA and other polyelectrolytes at high salt concentrations. Recent developments arising from studies of surface forces in ionic liquids that have been extended to include a wide variety of monovalent electrolytes reveal a hitherto unknown increase in the electrostatic decay length at high electrolyte concentrations. We hypothesise that the re-entrant behaviour of polyelectrolytes is driven by an increasing electrostatic decay length with increasing electrolyte concentration. Experiments: We survey numerous experiments in the literature on re-entrant swelling and calculate the effect of ion pairing on the electrostatic decay length in concentrated electrolytes. Findings: Re-entrant solubility is driven by an increasing electrostatic decay length at high salt concentrations and is universal across all polyelectrolytes.