Low-Frequency Spectra of 1-Methyl-3-octylimidazolium Tetrafluoroborate Mixtures with Poly(ethylene glycol) by Femtosecond Raman-Induced Kerr Effect Spectroscopy

Abstract

This is the first report on low-frequency spectra of ionic liquid (IL)/polymer mixtures using femtosecond Raman-induced Kerr effect spectroscopy. We studied mixtures of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm]­[BF4]) and poly­(ethylene glycol) (PEG) with M n = 400 (PEG400) at various concentrations. To elucidate the unique features of the IL/polymer mixture system, mixtures of PEG400 with a molecular liquid, 1-octhylimidazole (OIm), which is a neutral analog of the cation, were also studied. In addition, mixtures of [MOIm]­[BF4] with ethylene glycol (EG) and poly­(ethylene glycol) with M n = 4000 (PEG4000) were also investigated. The first moments of broad low-frequency spectra, mainly due to intermolecular vibrations for the [MOIm]­[BF4]/PEG400 and OIm/PEG400, increased slightly with increasing concentration of PEG400, indicating that microscopic intermolecular interactions, in general, are slightly enhanced. We also compared the [MOIm]­[BF4] mixtures with EG, PEG400, and PEG4000 at concentrations of 5 and 10 wt % PEG or EG. The low-frequency spectra of samples with the same concentrations were quite similar, but a comparison of the normalized spectra showed that the spectral intensity in the low-frequency region below ∼50 cm–1 of the [MOIm]­[BF4] mixtures with PEG400 and PEG4000 is somewhat lower than that of the [MOIm]­[BF4] mixtures with EG. Although the effect of the polymer is small compared to other polymer solution systems, this feature is attributed to a suppression of translational motion in the mixtures of [MOIm]­[BF4] with PEG compared to the mixtures of [MOIm]­[BF4] with EG due to the greater mass of PEG than EG. Density, surface tension, viscosity, and electrical conductivity were also estimated. From Walden plots, it was found that the [MOIm]­[BF4]/PEG4000 system showed more ideal electrical conductive behavior than the [MOIm]­[BF4]/PEG400 and [MOIm]­[BF4]/EG systems.

Exploring the Microscopic Aspects of 1-Methyl-3-octylimidazolium Tetrafluoroborate Mixtures with Formamide, N-Methylformamide, and N,N-Dimethylformamide by Multiple Spectroscopic Techniques and Computations

“…Figure shows the concentration dependence of the liquid properties (density ρ, viscosity η, electrical conductivity σ, and surface tension γ) for the [MOIm]­[BF 4 ] mixtures with FA, NMF, and DMF at 293 K. The values of the liquid properties of the mixtures are listed in Table S3. The results for neat [MOIm]­[BF 4 ], FA, NMF, and DMF are consistent with those in our previous studies ,,,,, and other reports. − Figure a shows that the ρ of the neat [MOIm]­[BF 4 ] is smaller than that of the neat FA but larger than those of the neat NMF and DMF. Therefore, with increasing X ML , ρ of [MOIm]­[BF 4 ]/FA increases but those of [MOIm]­[BF 4 ]/NMF and [MOIm]­[BF 4 ]/DMF decrease.…”

“…Figure 1 shows the concentration dependence of the liquid properties (density ρ, viscosity η, electrical conductivity σ, and surface tension γ) for the [MOIm][BF 4 ] mixtures with FA, NMF, and DMF at 293 K. The values of the liquid properties of the mixtures are listed in Table S3. The results for neat [MOIm][BF 4 ], FA, NMF, and DMF are consistent with those in our previous studies 32,36,58,63,91,92 and other reports. 93−102 1c exhibits the maximum peak at X ML = 0.9, which is similar to that in our previous study 58,92 and other reports.…”

“…The results for neat [MOIm][BF 4 ], FA, NMF, and DMF are consistent with those in our previous studies 32,36,58,63,91,92 and other reports. 93−102 1c exhibits the maximum peak at X ML = 0.9, which is similar to that in our previous study 58,92 and other reports. 2,103,104 In Figure 1d, the γ values for the [MOIm][BF 4 ] mixtures with NMF and DMF gradually increase with increasing X ML .…”

“…This phenomenon has also been observed in [MOIm][BF 4 ] mixtures with methanol, acetonitrile, dimethyl sulfoxide, 58 and poly(ethylene glycol). 92 This indicates that the ion concentration effect is dominant compared to the viscosity.…”

“…The η of the [MOIm][BF 4 ] mixtures almost logarithmically decreases with X ML , and this trend is almost similar to the results for [MOIm][BF 4 ] mixtures with H 2 O, benzene, methanol, acetonitrile, DMSO, and poly(ethylene glycol). 58,63,91,92 Given that the differences in η of the three amides relative to [MOIm][BF 4 ] are in the order η FA > η NMF > η DMF , the magnitude of the change in η by the alternation of X ML is also the smallest in [MOIm][BF 4 ]/FA and the largest in…”