title: On the concept of ionicity in ionic liquids.
abstract: 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.
authors: Department of Materials Engineering, Monash University, Clayton, Victoria, Australia. D.Macfarlane@sci.monash.edu.au
authors: Douglas R
authors: DR
authors: MacFarlane
authors: Maria
authors: M
authors: Forsyth
authors: Ekaterina I
authors: EI
authors: Izgorodina
authors: Andrew P
authors: AP
authors: Abbott
authors: Gary
authors: G
authors: Annat
authors: Kevin
authors: K
authors: Fraser
mesh_terms: D052578:Ionic Liquids / Q000737:chemistry*; D007477:Ions
chemical_list: D052578:Ionic Liquids; D007477:Ions