Liquid structure of 1-ethyl-3-methylimidazolium alkyl sulfates by X-ray scattering and molecular dynamics.

We report a joined X-ray diffraction and molecular dynamics study on the series of 1-ethyl-3-methylimidazolium alkyl sulfates (alkyl = ethyl, butyl, hexyl, octyl) ionic liquids. A general good agreement between experimental and theoretical structure functions has been found for each term of the series in all ranges of q values. Once the quality of the employed force field in reproducing structural data was tested, we used dynamics simulations to access information on morphology and properties of these systems. The series of ionic liquids presents nanoscale structural heterogeneity, whose size depends on the anion alkyl chain size. Analyzing our simulation data on the basis of alkyl chain length, we propose a structural model consistent with the presence of low q peaks.