## 3 Results and Discussion
Relative intensities of the IR bands are given in increments of 0.05; the scale bar is displayed in the upper left corner of the figure. TFS\({}^{-}\) anion, has required an expansion of the classical definition of hydrogen bonding. One of the intriguing aspects of C-H--O interactions is that the C-H bond tends to shorten as a result of the formation of blue-shifting hydrogen bonds. We demonstrate in Figure 3 that high pressure is a valuable method to probe pressure-enhanced blue-shifting of C-H hydrogen bonds in the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture. [PERSON]'s group and [PERSON]'s group indicated that the origin of both red-shifting and blue-shifting hydrogen bonds may be the same, and suggested that both types of hydrogen bonds result from a combination of electrostatic, polarization, charge transfer, dispersion, and exchange/steric repulsion forces between proton donors and acceptors [22; 23]. Figure 4 shows the infrared spectra of the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture attributed to the absorption of TFS\({}^{-}\) anions under various pressures. As the mixture is compressed to 0.4 GPa in Figure 4b, the 1270 cm\({}^{-1}\) (doublet) band narrowed and the band at 1165 cm\({}^{-1}\) splits into two  
Figure 3: IR spectra of the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture obtained under ambient pressure (curve a) and at 0.4 (curve b), 0.7 (curve c), 1.1 (curve d), 1.5 (curve e), 1.8 (curve f), and 2.5 GPa (curve g). Relative intensities of the IR bands are given in increments of 0.1; the scale bar is displayed in the upper left corner of the figure. distinct bands at ca. 1152 and 1175 cm\({}^{-1}\). These spectral changes may indicate a pressure-induced phase transition arising from both structural reorganization (due to ordered local structures) and a decrease in inhomogeneous broadening. The spectral features of the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture revealed in Figure 4 are almost identical to those of pure [BMIM][TFS]. In contrast to the bandwidth narrowing of asymmetric SO\({}_{3}\) stretching vibration at ca. 1270 cm\({}^{-1}\), the 1032 cm\({}^{-1}\) band (symmetric SO\({}_{3}\) stretching) displays anomalous bandwidth broadening upon compression in Figure 4b-g. It is likely that transverse optic (TO)-longitudinal optic (LO) splitting of the symmetric SO\({}_{3}\) stretching band plays a non-negligible role in Figure 4[11; 12; 24]. Figure 5 displays the IR spectra of a [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture after five washes with ethanol obtained under ambient pressure (curve a) and at 0.4 (curve b), 0.7 (curve c), 1.1 (curve d), 1.5 (curve e), 1.8 (curve f), and 2.5 GPa (curve g). As shown in Figure 5a,b, no appreciable changes in the spectral features of C-H vibrations occur as the sample is compressed to 0.4 GPa. This result is remarkably different from that is revealed for the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture in Figure 3b. It appears that the presence of nano-Al\({}_{2}\)O\({}_{3}\) has an influence on the supramolecular assemblies of the remaining ILs on the surface of Al\({}_{2}\)O\({}_{3}\) after five washes and under high pressures, as revealed in Figure 5. The nano-Al\({}_{2}\)O  
Figure 4: IR spectra of the [BMIM][TFS]/Al\({}_{2}\)O\({}_{3}\) mixture obtained under ambient pressure (curve a) and at 0.4 (curve b), 0.7 (curve c), 1.1 (curve d), 1.5 (curve e), 1.8 (curve f), and 2.5 GPa (curve g). Relative intensities of the IR bands are given in increments of 0.25; the scale bar is displayed in the upper left corner of the figure. surfaces may weaken the cation/anion interactions in the interfacial area as a result of the formation of enhanced ionic liquid/particle surface interactions under high pressures. The Al\({}_{2}\)O\({}_{3}\)/ionic liquid interactions may also affect the hydrogen-bonded network of interfacial [BMIM][TFS] under high pressures.