The self-assembly of water reverse micelles with imidazolium ionic liquids in supercritical carbon dioxide: A molecular dynamics simulation study

Abstract

Molecular dynamics (MD) simulations were employed to investigate the self-assembly of water reverse micelles (RMs) with imidazolium ionic liquids (ILs) stabilized by dodecyl polyoxyethylene (3) polyoxypropylene (6) ether (LS-36) in supercritical carbon dioxide (scCO2) at 308 K and 20 MPa. The study explored the impact of various factors, including the IL concentration, the alkyl chain length of the imidazolium cations (1-ethyl-3-methylimidazolium [EMIM]+, 1-octyl-3-methylimidazolium [OMIM]+), and the anion type (bis(trifluoromethylsulfonyl)imide [NTf2]-, tetrafluoroborate [BF4]-, acetate [ACE]-) on the solubilization of ILs by water reverse micelles. The findings revealed that water, ILs, and the surfactant formed spherical RMs in the fluid phase, with varying structures depending on the hydrophobicity of the IL. The presence of ILs was found to expedite the self-assembly process and increase the number of assembled surfactants. Higher IL concentrations resulted in greater water content in the polar core of the RMs and reduced water solubility in scCO2. The intermolecular interactions occurring between components of the systems as well as dynamical properties are discussed in terms of radial distribution functions, density distribution, hydrogen bond number and lifetime, number of contacts, and self-diffusion coefficients.