Probing the Heterogeneity of Ionic Liquids in Solution through Phenol‐Water Phase Behavior.

Abstract

AbstractPhenol‐water system is important considering its resemblances to biological systems. Here, we explore this phenol‐water system to get crucial information on ionic liquids (ILs). Comparative studies on the effect of high melting salts, micelles and ionic liquids (ILs) reveal interesting facts: while normal high melting salts such as KCl, CsCl and ionic surfactants (above and below critical micelle concentration (CMC)) show only an enhancement of critical solution temperature (CST) along with no substantial change in the shape of phase diagram, TX‐100 shows an interesting trend. Below CMC, TX‐100 shows normal trend while complete deviation is observed above CMC. When IL is added at various concentrations in the phenol‐water system, the concentration‐dependent effect on the phase diagram is observed. While at the low concentration, it follows the normal trend, at higher concentration phase diagram deviates drastically. The concentration at which this deviation is observed is termed here as Critical Ionic Liquid Aggregation Concentration (CILAC). Above CILAC, ILs exert an effect that resembles the effect of TX‐100 micelles in the phenol‐water phase diagram. Viscosity measurements of the system substantiate these data. Based on our observations, we propose that imidazolium chloride ILs constitute elliptical aggregates similar to TX‐100 (having ∼300 Å length) in solution above CILAC. To the best of our knowledge, this is the first report on the possible shape and size of ILs aggregation in solution.