Application of hole theory to define ionic liquids by their transport properties.

Eutectic mixtures of quaternary ammonium salts with Lewis or Brønsted acids have been described as ionic liquid, but doubt exists over the compositional range for which this description is valid. In the current work, the conductivity, viscosity, density, and surface tension of a number of glycolic mixtures with choline chloride are measured over the mole fraction range 0 to 0.33. The data are fitted to hole theory, and it is proposed that the composition at which the measured conductivity matches the theoretical value is the point at which hole mobility becomes the dominant mechanism for charge mobility. For the mixtures of ethylene glycol and butanediol, this occurs at a ChCl mole fraction of approximately 0.2.