Solvent and rotational relaxation of Coumarin-153 in a micellar solution of a room-temperature ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, in ethylammonium nitrate

► 1-Butyl-3-methylimidazolium octyl Sulfate (bmimOs) forms micelle in EAN. ► The CMC of bmimOs in EAN was nine times greater than the CMC of bmimOs in water. ► Micelle formation has little effect on the interaction between the ions of RTIL. ► Even at three times CMC the average solvation time increases only by a factor of 4.65.