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Cosolvent-tuned interactions in ionic liquids: A vibrational and quantum-chemical study of ethylene glycol ratio effects
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DOI：10.1016/j.jil.2026.100190.png)
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Abstract
En 中文
Ionic liquids (ILs) are attractive media for CO2 capture but remain limited by viscosity and cost. Blending ILs with ethylene glycol (EG) is a practical route to mitigate these constraints, yet the molecular origins of cosolvent effects and their dependence on composition are not well resolved. We combine Fourier-transform infrared (FT-IR) spectroscopy with quantum-chemical (DFT) analysis to elucidate how the IL:EG molar ratio modulates intermolecular interactions and electronic structure. Computed vibrational frequencies enable mode assignment and deconvolution of overlapping bands, revealing systematic, ratio-dependent shifts and broadenings in (i) EG O-H stretching, (ii) cation and EG C-H stretchings (imidazolium C2-H, C4-H, C5-H, methyl and ethyl groups,-CH2 of EG), (iii) anion signature modes (e.g., CN motifs), and (iv) EG C-O and C-C stretchings, consistent with the redistribution of hydrogen-bonding networks. Molecular electrostatic potential (MESP) maps quantify attenuation of extreme potential regions with increasing EG, indicating progressive screening of cation-anion electrostatic interactions. Quantum Theory of Atoms in Molecules (QTAIM) identifies emergent bond critical points between EG and the IL ions, while Reduced Density Gradient-Noncovalent Interaction (RDG-NCI) analysis differentiates strong directional hydrogen bonds from dispersive contacts across compositions. Together, these results show that EG fraction controls a switch from predominantly ion-ion to mixed ion-EG coordination, altering local polarity and polarizability that underlie the observed FT-IR trends. The framework provides composition-structure-spectrum relationships that can guide rational selection of IL:EG ratios to balance favorable molecular interactions with practical performance targets in scalable CO2 capture systems.
Keywords:
IL-cosolvent
FT-IR
H -bonding
QTAIM analysis
Salting-out effect
DAC
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