Evidence of nanostructuration from the heat capacities of the 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid series

Rocha, Marisa A.A.; Coutinho, João A. P.; Santos, Luı́s M. N. B. F.

doi:10.1063/1.4820825

Cited by 37 publications

(32 citation statements)

References 29 publications

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“…The obtained stationary value of the glass transition temperature after the CAS can be associated with the unchangeable polar network grid type above the CAS, which seems to govern the relative stability between the glassya nd liquid states. This observation is in agreement with the structuration model derived from other experimental [22] and computational data, [23,24] which have shown that for both IL series at rend shift occurred at n = 6, the so-called criticala lkyl size (CAS), [11,25,26] due to an intensification of the nanostructuration in the liquid phase.…”

Section: Resultssupporting

confidence: 91%

Nanostructuration Effect on the Thermal Behavior of Ionic Liquids

Rodrigues

Santos

2016

ChemPhysChem

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This work shows how the nanostructuration of ionic liquids (ILs) governs the glass and melting transitions of the bistriflimide imidazolium-based [Cn C1 im][NTf2 ] and [Cn Cn im][NTf2 ] series, which highlights the trend shift that occurs at the critical alkyl size (CAS) of n=6. An initial increase in the glass temperature (Tg ) with an increase in the alkyl side chain was observed due to the intensification of the dispersive interactions (van der Waals). Above the CAS, the -CH2 - increment has the same effect in both glass and liquid states, which leads to a plateau in the glass transition after nanostructuration. The melting temperature (Tm ) of the [Cn C1 im][NTf2 ] and [Cn Cn im][NTf2 ] series presents a V-shaped profile. For the short-alkyl ILs, the -CH2 - increment affects the electrostatic ion pair interactions, which leads to an increase in the conformational entropy. The -CH2 - increment disturbs the packing ability of the ILs and leads to a higher entropy value (ΔslSm○ ) and consequently a decrease in Tm . Above the CAS, the -CH2 - contribution to the melting temperature becomes more regular, as a consequence of the nanostructuration of the IL into polar and nonpolar domains. The dependence of the alkyl chain on the temperature, enthalpy, and entropy of melting in the ILs above the CAS is very similar to the one observed for the alkane series, which highlights the importance of the nonpolar alkyl domains on the ILs thermal behavior.

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Section: Resultssupporting

confidence: 91%

Nanostructuration Effect on the Thermal Behavior of Ionic Liquids

Rodrigues

Santos

2016

ChemPhysChem

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“…Moreover, this macroscopic segregation behaviour has been shown to be a major feature in the ionic liquid bulk phase and as reflected in the thermophysical properties of ILs. [66][67][68][69][70][71][72][73] Similar trend shifts were observed in the IL viscosity, [66][67] surface tension, 68 vapour pressure, 69,70 heat capacity, 71 among others. 72,73 It is, however, thought-provoking to highlight that different trends on the IL acidity with increasing alkyl chain length have also been reported.…”

Section: Experimental Kamlet-taft Solvatochromic Parameterssupporting

confidence: 71%

Hydrogen-bond acidity of ionic liquids: an extended scale

Kurnia

Lima

Cláudio

et al. 2015

Phys. Chem. Chem. Phys.

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102

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One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related to the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency in the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf 2 ] − )-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (E HB ) play the major role, the electrostaticmisfit interactions (E MF ) and van der Waals forces (E vdW ) also contribute, admittedly in a lower extent, towards the hydrogen-bond acidity of ILs. The new extended scale provided for the hydrogen-bond acidity of ILs is of high value for the design of new ILs for task-specific applications. † Electronic supplementary information (ESI) available: Comparison between experimental and literature solvatochromic values; correlation between experimental and predicted hydrogen-bond acidity; equation to calculate the absolute relative deviation. See

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“…They report on water solubility in a series of asymmetric and symmetric [CnCxim][NTf2] ILs (where n is up to 21 and x = 1 or n), extending their study of symmetric cations [36][37][38]. In order to analyse their solubility data, Density Functional theory calculations were also performed.…”

Section: [Saielli]mentioning

confidence: 99%

“…Since the appearance of the first experimental [4] and computational [2,3] proposals for such an organization, numerous studies provided more and more compelling evidences of this specific architecture. Several aspects have been explored in the last few years, including the role of alkyl chain length [5,9,[12][13][14][15][16][25][26][27][28][29][30], charged moieties chemical nature [5,15,16], polarity of the tail [12,20,21,[31][32][33], symmetry of the cation [34][35][36][37][38], effect of temperature [14,23,39] etc. It is stated that there is a strong correlation between structural complexity and performances of ILs.…”

mentioning

confidence: 99%