Structural Reorganization of Imidazolium Ionic Liquids Induced by Pressure-Enhanced Ionic Liquid—Polyethylene Oxide Interactions

Abstract

Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C–H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM]+ and [HMIM]+. The pressure-induced phase transition of pure 1-butyl-3-methylimidazolium bromide ([BMIM]Br) is observed at a pressure of 0.4 GPa. Pressure-enhanced [BMIM]Br-PEO interactions may assist PEO in dividing [BMIM]Br clusters to hinder the aggregation of [BMIM]Br under high pressures. The C–H absorptions of pure 1-hexyl-3-methylimidazolium bromide [HMIM]Br do not show band narrowing under high pressures, as observed for pure [BMIM]Br. The band narrowing of C–H peaks is observed at 1.5 GPa for the [HMIM]Br-PEO mixture containing 80 wt% of [HMIM]Br. The presence of PEO may reorganize [HMIM]Br clusters into a semi-crystalline network under high pressures. The differences in aggregation states for ambient-pressure phase and high-pressure phase may suggest the potential of [HMIM]Br-PEO (M.W.~900,000) for serving as optical or electronic switches.

Pressure-Dependent Clustering in Ionic-Liquid-Poly (Vinylidene Fluoride) Mixtures: An Infrared Spectroscopic Study

“…Combining the IR technique and high pressures may result in pressure-enhanced interactions. As reported in previous studies [ 32 , 33 , 34 , 35 , 36 ], the associated structures of ILs were influenced by the addition of PEO [ 32 ] and DNA [ 33 ] under high pressure. As the pressure was applied, the polymer (PEO or DNA) disturbed the clustering of the ILs, as polymers and ILs interact with specific pressure-enhanced forces.…”

“…Figure 1 shows infrared spectra of ( Figure 1 a) pure [HEMIm][TFSI] mixtures of [HEMIm][TFSI]-PVdF containing ( Figure 1 b) 30, ( Figure 1 c) 20, and ( Figure 1 d) 10 wt% [HEMIm][TFSI], as well as ( Figure 1 e) pure PVdF obtained at ambient pressure. The IR spectra of pure [HEMIm][TFSI] in Figure 1 a show broad O–H absorptions, two main imidazolium C–H bands, and several alkyl C–H peaks at 3300–3700, 3050–3250, and 2800–3000 cm −1 , respectively, at ambient pressure [ 25 , 32 , 33 , 34 , 35 , 36 ]. As shown in Figure 1 a, the O–H absorption also displays a shoulder peak at ca.…”

“…In contrast to C–H absorption, the O–H stretching bands show a redshift as the pressure is increased from ambient pressure to 2.5 GPa, as shown in Figure 3 . The results in Figure 3 demonstrate that C 2 –H and C 4,5 –H may suffer pressure-induced changes in weak hydrogen-bonding interactions (a blueshift) with anions [ 32 , 33 , 34 , 35 , 36 ]. Conversely, the pressure-induced redshift of the O–H vibrational bands may result from both pressure-enhanced strong hydrogen bonding and the formation of larger cationic clusters (lower frequencies accompanied by band broadening) via pressure-induced association [ 32 , 33 , 34 , 35 , 36 ].…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…The third of the directions officially accepted in the PCCP Section, is represented by only 11 articles [ 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ], including 9 Originals and 2 Reviews. Their distribution by years of publication is presented in Table 4 .…”

“…It also presents new perspectives based on existing data. In addition to these review articles, research articles [ 56 , 57 , 58 ] are devoted to ionic liquids. The rest of the publications of this section are completely dissimilar from each other in thematic respect, and it is very difficult (if not possible at all) to find something in common between them (except that they can all be attributed to the field of electrochemistry).…”