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Micelle Formation in Aqueous Solutions of Room Temperature Ionic Liquids: A Molecular Dynamics Study
1-Alkyl-3-methylimidazolium
cations in the presence of water are
used as a test system to study by molecular dynamics the formation
of micelles in aqueous mixtures of highly anisotropic room temperature
ionic liquids (IL). Structural properties, i.e., radial distribution
functions (RDF) and transport parameters, such as diffusion coefficients
and conductivities, are computed as a function of the IL/water mole
fraction. The concentration plots reveal a sharp change of the slope
of both the cation self-diffusion coefficient and the first peak of
the head–head RDF at approximately the same value of the concentration.
This transition, considered as a measure of a critical micellar concentration,
appears only for the most anisotropic systems, composed of longer
alkyl chains. The formation of the micelles is confirmed from the
analysis of the tail–tail and cation–water RDFs. As
a general result, we found that the larger the anisotropy of the ionic
liquid the lower the critical concentration and the larger the proportion
of monomers forming part of the micelles. The molecular dynamics predictions
are in line with the experimental evidence reported for these systems