Raman band shape analysis of cyanate-anion ionic liquids

Penna, Tatiana C.; Faria, Luiz F. O.; Ribeiro, Mauro C. C.

doi:10.1016/j.molliq.2015.06.038

Cited by 22 publications

(29 citation statements)

References 55 publications

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“…For a better discussion, the main Raman bands and intensity ratios for carbon nanotubes and their dispersions in IL are collected in table 1. In our case, the main absorptions in the Raman spectrum of neat [EMIM][DCA] (Figure 4a) are observed at 2198.4 cm-1, assignable to C-N stretching of the dicyanamide anion[40] and 2949.2 cm-1, assignable to C-H stretching of the imidazolium cation[41]. The first absorption is shifted to lower values, at 2192.7 cm-1 for the dispersions containing SWCNTs and MWCNTs, but when aligned-MWCNTs are dispersed this peak is found at 2189.9 cm-1.…”

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confidence: 59%

Rheological study of new dispersions of carbon nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

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Arias‐Pardilla

et al. 2019

Journal of Molecular Liquids

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Dispersions of three different types of carbon nanotubes in a 1 wt.% proportion in the low viscosity 1-ethyl-3-methylimidazolium ([EMIM][DCA]) ionic liquid have been obtained. The neat ionic liquid presents Newtonian behavior, but the addition of carbon nanotubes increases the viscosity with respect to [EMIM][DCA] in the following order: Single-Walled Carbon Nanotubes (SWCNTs) > aligned Multi-Walled Carbon Nanotubes (aligned-MWCNTs) > Multi-Walled Carbon Nanotubes (MWCNTs), and the resulting fluids show non-Newtonian behavior. SWCNTs and MWCNTs dispersions present shear thinning with increasing shear rate, but a shear thickening effect for aligned-MWCNTs at intermediate shear rate values at room temperature has been observed. This effect disappears at 100 ºC. The thermal response of the viscosity of [EMIM][DCA] and the CNTs-IL dispersions can be fitted to the Arrhenius model. For [EMIM][DCA] and the dispersion with MWCNTs the viscous behavior prevails at low frequencies, with a cross point at a critical frequency value which decreases with increasing temperature. However, the dispersions of SWCNTs and aligned-MWCNTs present storage modulus values higher than loss modulus in the whole range of frequency.

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confidence: 59%

Rheological study of new dispersions of carbon nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

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Arias‐Pardilla

et al. 2019

Journal of Molecular Liquids

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“…The Raman spectra recorded during stepwise heating from 210 to 260 K is a superposition of the spectra of crystals I and II, the latter contribution increasing with temperature. In previous publications, Raman and IR spectra of [C 2 C 1 im][N(CN) 2 ] have been discussed in the spectral range of the symmetric and antisymmetric CN stretching modes of the anion, ν s (CN) and ν as (CN). It is expected that these vibrations act as probes of the local environment experienced by the anion.…”

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confidence: 99%

Low-Temperature Phase Transitions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Dicyanamide

2019

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Several calorimetric measurements have shown that 1-ethyl-3-methylimidazolium dicyanamide, [C2C1im][N(CN)2], is a glass-forming liquid, even though it is a low-viscous liquid at room temperature. Here, we found slow crystallization during cooling of [C2C1im][N(CN)2] along Raman spectroscopy measurements. The low-frequency range of the Raman spectrum shows that the same crystalline phase is obtained at 210 K either by cooling or by reheating the glass (cold-crystallization). Another crystalline phase is formed at ca. 260 K just prior the melting at 270 K. X-ray diffraction and calorimetric measurements confirm that there are two crystalline phases of [C2C1im][N(CN)2]. The Raman spectra indicate that polymorphism is related to [C2C1im]+ with the ethyl chain on the plane of the imidazolium ring (the low-temperature crystal) or nonplanar (the high-temperature crystal). The structural reason for the glass-forming ability of [C2C1im][N(CN)2], despite the relatively simple molecular structures of the ions, was pursued by quantum chemistry calculations and molecular dynamics (MD) simulations. Density functional theory calculations were performed for ionic pairs in order to draw free-energy surfaces of the anion around the cation. The MD simulations using a polarizable model provided maps of occurrence of anions around cations. Both the quantum and classical calculations suggest that the delocalization of preferred positions of the anion around the cation, which adopts different conformations of the ethyl chain, is on the origin of the crystallization being hampered during cooling and the resulting glass-forming ability of [C2C1im][N(CN)2].

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“…Table 2 reports select stretching frequencies for the nonhydrated (χ H2O = 0.0) [EMIM][SCN] system that were experimentally and theoretically determined within the present study and in previous Raman investigations. 27,66,75,102 Additionally, this table reports experimental frequency shifts upon hydration with a mole fraction of χ H2O = 0.9 and theoretical Boltzmann weighted frequency shifts associated with the monohydrated structures depicted in Figure 2. Further information about the Boltzmann weighted frequencies are provided in the Supporting Information, along with the harmonic vibrational frequencies and Raman scattering activities for all structures.…”

Section: ■ Frequency Analysismentioning

confidence: 99%

Intermolecular Interactions and Vibrational Perturbations within Mixtures of 1-Ethyl-3-methylimidazolium Thiocyanate and Water

et al. 2018

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A Raman spectroscopic analysis of the room temperature ionic liquid 1-ethyl-3-methlimidazolium thiocyanate, [EMIM][SCN], has revealed that certain stretching vibrations associated with both the anion and cation shift to higher energy (or blue-shift) as water is introduced to the system (by up to 15 cm −1 for a CH stretching mode associated with EMIM + and up to 12 cm −1 for the CS stretch of SCN − ). Density functional theory was employed to gain molecular level insight into the origins of these spectral perturbations by computing changes in the structures, energetics, and harmonic vibrational frequencies of the [EMIM][SCN] ion pair as a single explicit water molecule was added to the system. The computed harmonic vibrational frequency shifts for the low-energy structures of the ion pair and the corresponding monohydrated complex reproduce the experimentally observed trends. These results indicate that the donation of a hydrogen bond from water to the N atom of SCN − produces the blue-shifts associated with the CN and CS stretching modes. In contrast, the vibrational frequency shifts associated with CH stretches of EMIM + do not appear to require a direct interaction with the water molecule.

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Raman band shape analysis of cyanate-anion ionic liquids

Cited by 22 publications

References 55 publications

Rheological study of new dispersions of carbon nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

Rheological study of new dispersions of carbon nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

Low-Temperature Phase Transitions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Dicyanamide

Intermolecular Interactions and Vibrational Perturbations within Mixtures of 1-Ethyl-3-methylimidazolium Thiocyanate and Water

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