The hydrogen bonding structures of room-temperature ionic liquids 1,3-dimethylimidazolium methyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate have been studied by infrared spectroscopy. High-pressure infrared spectral profiles and theoretical calculations allow us to make a vibrational assignment of these compounds. The imidazolium C-H bands of 1,3-dimethylimidazolium methyl sulfate display anomalous non-monotonic pressure-induced frequency shifts. This discontinuity in frequency shift is related to enhanced C-H...O hydrogen bonding. This behavior is in contrast with the trend of blue shifts in frequency for the methyl C-H stretching mode at ca. 2960 cm(-1). Our results indicated that the imidazolium C-H groups are more favorable sites for hydrogen bonding than the methyl C-H groups in the pure 1,3-dimethylimidazolium methyl sulfate. Nevertheless, both methyl C-H and imidazolium C-H groups are favorable sites for C-H...O hydrogen bonding in a dilute 1,3-dimethylimidazolium methyl sulfate/D(2)O mixture. Hydrogen bond-like C-H...F interactions were observed between PF(6)(-) and H atoms on the alkyl side chains and imidazolium ring for 1-butyl-3-methylimidazolium hexafluorophosphate.
Thin silicate platelets in a dimension of approximately 80 × 80 × 1 nm 3 are isolated for the first time by a newly developed process involving one-step exfoliation of natural montmorillonite clay and toluene/aqueous NaOH extraction. The platelets are observed to be polygon shape by transmission electron microscopy (TEM) and round bent-leaf shape by dynamic force microscopy (DFM). Individual platelets possessing high-aspectratio dimension and ionic character are able to self-assemble into microscale fiber bundles after water evaporation. The self-stacking mechanism indicated strong face-to-face ionic charge stacking propensity in triggering a vertical growth. Regularity of fibrous bundles in an average 5 µm length has been observed.
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