Simple and complex forms of disorder in ionic liquids

Abstract

An analysis of the structural features of high and room temperature liquids is proposed, which attempts to explain the differences in disorder between these two types of systems by the particles shape and the ratio of the molecular size to the temperature. This is achieved by the study of different types of models, by computer simulations and liquid state integral equation techniques. The comparative study of the correlation functions and structure factors explains the origin of the pre-peak observed in room temperature ionic liquids, and clarifies the respective roles of the electrostatic and neutral part of the various atom–atom interactions. The study equally clarifies the differences between the fluctuations, and in particular critical fluctuations, and the structural micro-heterogeneity. The excellent agreement between the theory and the simulations, as opposed to the poorer agreement often observed in case of associated molecular liquids (such as water and alcohols), illustrates the conceptual difference between free and bound charges, ionic and molecular liquids. It is argued herein that different forms of disorders are associated to this underlying difference.