Aggregation Behavior of Triton X‑100 with a Mixture of Two Room-Temperature Ionic Liquids: Can We Identify the Mutual Penetration of Ionic Liquids in Ionic Liquid Containing Micellar Aggregates?

In this manuscript, we have characterized two different micellar aggregates containing all nonvolatile components. We have shown (i) the effect of ethylammonium nitrate (EAN) addition on the properties of micellar solution of Triton X-100 in 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF₆) and (ii) the effect of bmimPF₆ addition on the properties of micellar solution of Triton X-100 in EAN. To investigate the effect, we have used ¹H NMR, pulsed-field gradient spin–echo NMR (PFGSE NMR), and methyl orange (MO) and coumarin 153 (C-153) as absorption and emission probes, respectively. The penetration of added EAN inside the Triton X-100/bmimPF₆ micellar aggregates is indicated by (i) red shift in both the absorption spectra of MO and emission spectra of C-153 and (ii) downfield shift of proton signals of ethylene oxide units in Triton X-100. On the other hand, ¹H NMR and PFGSE NMR indicates the penetration of added bmimPF₆ inside the Triton X-100/EAN micellar aggregates. However, the constancy of both the absorption spectra of MO and emission spectra of C-153 indicates that the microenvironment around the probe molecules remains unaffected. We have also investigated the effect of micelle formation and the effect of penetration of ionic liquids (ILs) in micellar aggregates, on the solvation dynamics of C-153. The solvent relaxation around C-153 gets retarded on going from neat ILs to the micellar solution of Triton X-100 in ILs. In addition to this, we have also observed that with the addition of EAN in Triton X-100/bmimPF₆ micellar aggregates the solvation dynamics becomes faster, whereas with the addition of bmimPF₆ in Triton X-100/EAN micellar aggregates we did not observe any notable change in solvation dynamics. This observation further supports the conclusions drawn from UV–visible and NMR studies.