Pressure-dependent cationic associations of ionic liquids with bentonite nanoclay

Burba, Christopher M.; Singh, Dheeraj K.; Chiou, Yen-Wen; Wang, Teng-Hui; Chang, Hai-Chou

doi:10.1016/j.jil.2023.100067

Cited by 1 publication

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“…Whereas the temperature effect of cation–cation clustering has been widely studied, the influence of pressure on the (c–a) and (c–c) cluster distribution remains rarely explored. − Thus, it is the purpose of this work to study cationic cluster formation in hydroxy-functionalized ILs by means of pressure-dependent infrared spectroscopy. Herein, we addressed several questions concerning the stability of (c–a) and (c–c) clusters depending on pressure up to 2.5 GPa.…”

Section: Introductionmentioning

confidence: 99%

Hydroxy-Functionalized Ionic Liquids under Pressure: The Influence on Hydrogen Bonding between Ions of Opposite and Like Charges

Hunger,

Ludwig,

Chuang

et al. 2024

J. Phys. Chem. B

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Hydroxy functionalization of cations in ionic liquids (ILs) can lead to formation of hydrogen bonds between their OH groups, resulting in so-called (c−c) H-bonds. Thereby, the (c−c) H-bonds compete with regular H-bonds (c−a) between the OH groups and the anions. Polarizable cations, weakly interacting anions, and long alkyl chains at the cation support the propensity for the formation of (c−c) H-bonds. At low temperatures, the equilibrium between (c− c) and (c−a) H-bonds is strongly shifted in favor of the cation−cation interaction. Herein, we clarify the pressure dependence on (c−c) and (c−a) H-bond distributions in the IL 1-(2-hydroxyethyl)-3-methylimidazolium hexafluorophosphate [HOC 2 C 1 Im][PF 6 ], in mixtures of [HOC 2 C 1 Im][PF 6 ] with the nonhydroxy-functionalized IL 1-propyl-3-methylimidazolium hexafluorophosphate [C 3 C 1 Im][PF 6 ] and in [HOC 2 C 1 Im][PF 6 ] including trace amounts of water. The infrared (IR) spectra provide clear evidence that the (c−c) H-bonds diminish with increasing pressure in favor of the (c−a) H-bonds. Adding trace amounts of water results in enhanced (c−c) clustering due to cooperative effects. At ambient pressure, the water molecules are involved in the (c−c) H-bond motifs. Increasing pressure leads to squeezing them out of H-bond clusters, finally resulting in demixing of water and the IL at the microscopic level.

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