Self-assembly in aqueous solutions of imidazolium ionic liquids and their mixtures with an anionic surfactant

Experimental data on micellization in aqueous solutions of 1-alkyl-3-methylimidazolium salts [Cnmim]X and their mixtures with sodium dodecyl sulfate (NaDS) are reviewed. New results (the critical micelle concentration and enthalpy of micellization) are presented for mixtures of [C4mim]PF6, [C6mim]BF4, [C6mim]Br and [C10mim]Br with NaDS. Our data cover a wide range (from 0 to 0.9) of solvent-free based mole fractions of ionic liquid (IL). Even very small addition of ILs substantially decreases the cmc of NaDS due to the combined effect of electrostatic and hydrophobic interactions, and formation of mixed micelles. It is shown that the quasichemical aggregation model by Nagarajan and Ruckenstein may be successfully applied to aqueous solutions of long-chain ILs and their mixtures with NaDS. The local structure of micelles is obtained from all-atom MD simulations for [Cnmim]Br and [Cnmim]X + NaDS in aqueous medium.

Graphical abstractLeft: critical micelle concentration of NaDS in aqueous solutions containing [C4mim]PF6, [C6mim]BF4 or [C10mim]Br versus the ionic liquid solvent-free mole fraction; T = 298.15 K. Right: mixed micelle of NaDS–[C10mim]Br.Figure optionsDownload full-size imageDownload as PowerPoint slide