Aggregation of imidazolium based ionic liquids in binary methanol–water solvents: A linear solvation free energy relationship study

Abstract

Aggregation behavior of an imidazolium based ionic liquid (IL), namely 1-dodecyl-3-methylimidazolium chloride [C 12mim][Cl] and a surfactant with the same aliphatic chain, dodecyl trimethylammonium chloride (DTAC), are studied and compared in different mole fractions of methanol–water binary solvents using conductometry. From the conductivity data, micellar parameters including critical micelle concentration (CMC), degree of counter ion dissociation (α) and Gibbs free energy of micellization (ΔG°mic) for both species were calculated as a function of methanol mole fraction. It was found that similar to the surfactant DTAC, the ionic liquid [C 12mim][Cl] forms micellar aggregation in pure water and methanol as well as in their binary mixtures. The CMC values for both compounds were increased up to a methanol mole fraction of 0.5 and then decreased at higher mole fractions. This was attributed to the preferential solvation and formation of methanol–water cluster in binary mixed solvents. The changes in CMC of [C 12mim][Cl] and DTAC as a function of methanol mole fraction were also described by changing in solvatochromic properties of solvents through linear solvation free energy relationship (LSFER) study. A linear relationship between log (CMC) and two solvatochromic Kamlet-Taff parameters including polarity/polarizability (π*) and hydrogen-bond basicity (β) was observed.