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On the concept of ionicity in ionic liquids

journal contribution
posted on 01.01.2009, 00:00 authored by D MacFarlane, Maria ForsythMaria Forsyth, E Izgorodina, A Abbott, G Annat, K Fraser
Ionic liquids are liquids comprised totally of ions. However, not all of the ions present appear to be available to participate in conduction processes, to a degree that is dependent on the nature of the ionic liquid and its structure. There is much interest in quantifying and understanding this ‘degree of ionicity’ phenomenon. In this paper we present transport data for a range of ionic liquids and evaluate the data firstly in terms of the Walden plot as an approximate and readily accessible approach to estimating ionicity. An adjusted Walden plot that makes explicit allowance for differences in ion sizes is shown to be an improvement to this approach for the series of ionic liquids described. In some cases, where diffusion measurements are possible, it is feasible to directly quantify ionicity via the Nernst–Einstein equation, confirming the validity of the adjusted Walden plot approach. Some of the ionic liquids studied exhibit ionicity values very close to ideal; this is discussed in terms of a model of a highly associated liquid in which the ion correlations have similar impact on both the diffusive and conductive motions. Ionicity, as defined, is thus a useful measure of adherence to the Nernst–Einstein equation, but is not necessarily a measure of ion availability in the chemical sense.

History

Journal

Physical chemistry chemical physics

Volume

11

Issue

25

Pagination

4962 - 4967

Publisher

Royal Society of Chemistry

Location

Cambridge, England

ISSN

1463-9076

eISSN

1463-9084

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2009, Owner Societies