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Faraday Discuss. 2017 Jul 1;199:239-259. doi: 10.1039/c6fd00250a. Epub 2017 May 3.

Underscreening in concentrated electrolytes.

Author information

1
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA. alphalee@g.harvard.edu.
2
Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UK. susan.perkin@chem.ox.ac.uk.
3
Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UK. susan.perkin@chem.ox.ac.uk and Department of Inorganic and Analytical Chemistry, University of Geneva, 1205 Geneva, Switzerland.

Abstract

Screening of a surface charge by an electrolyte and the resulting interaction energy between charged objects is of fundamental importance in scenarios from bio-molecular interactions to energy storage. The conventional wisdom is that the interaction energy decays exponentially with object separation and the decay length is a decreasing function of ion concentration; the interaction is thus negligible in a concentrated electrolyte. Contrary to this conventional wisdom, we have shown by surface force measurements that the decay length is an increasing function of ion concentration and Bjerrum length for concentrated electrolytes. In this paper we report surface force measurements to test directly the scaling of the screening length with Bjerrum length. Furthermore, we identify a relationship between the concentration dependence of this screening length and empirical measurements of activity coefficient and differential capacitance. The dependence of the screening length on the ion concentration and the Bjerrum length can be explained by a simple scaling conjecture based on the physical intuition that solvent molecules, rather than ions, are charge carriers in a concentrated electrolyte.

PMID:
28466925
DOI:
10.1039/c6fd00250a

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