Thermodynamics of long-chain 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids

Abstract

The heat capacities in the temperature range (5 to 370) K and the parameters of solid-phase phase transitions and fusion were determined for three [Cnmim][NTf2] (n = 10, 14, 16) ILs. The temperature-dependent vapour pressures of [C14mim][NTf2] and [C16mim][NTf2] were measured with a Knudsen effusion apparatus combined with a quartz crystal microbalance. Thermodynamic properties of these compounds in the crystal, liquid, and gas states were derived from the obtained data. The results obtained in this work were combined to those available in the literature for the short-chain homologues to discuss regularities in thermodynamic properties of the series. While some properties demonstrate simple linear dependence on the alkyl chain length, a more complicated behaviour with strong nonlinearity or a break at n = 6 is observed for others.

Calculation of the Isobaric Heat Capacities of the Liquid and Solid Phase of Organic Compounds at and around 298.15 K Based on Their “True” Molecular Volume

“…In addition, a number of further IL data have been provided by the National Institute of Standards and Technology [262]. In the meantime, a number of recent papers have been published presenting further heat-capacity data of ILs [263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287].…”

Quantifying intermolecular interactions of ionic liquids using cohesive energy densities

“…Quantum mechanical and statistical thermodynamic calculations on ionic vapour neutral ion pairs have been used to obtain gas-phase heat capacities for [C n C 1 Im][NTf 2 ] ( n = 2, 4, 6, 8) [ 139 ]. Correlations developed from these values have then been used to obtain Δ g l C p for [C n C m Im][NTf 2 ] ILs, ranging from Δ g l C p = −112 J K −1 mol −1 for [C 2 C 1 Im][NTf 2 ] to Δ g l C p = −203 J K −1 mol −1 for [C 10 C 10 Im][NTf 2 ] [ 129 , 130 , 132 , 133 , 135 ]. Clearly, there are very large and unsatisfactory discrepancies between these Δ g l C p values and the widely used Δ g l C p = −100 J K −1 mol −1 value; these differences can lead to significant variation in Δ vap H values, up to 20 kJ mol −1 for ILs with long alkyl chains [ 111 ].…”

“…For ILs, both Knudsen effusion [ 56 , 86 – 89 , 91 , 119 , 129 – 133 , 135 , 151 , 152 ] and Langmuir [ 31 , 57 , 63 , 64 , 71 – 77 , 80 , 96 , 106 – 128 ] vaporization methods have been used to obtain Δ vap H . For Langmuir (i.e.…”

“…For ILs, both Knudsen effusion [56,[86][87][88][89]91,119,[129][130][131][132][133]135,151,152] and Langmuir [31,57,63,64,[71][72][73][74][75][76][77]80,96, vaporization methods have been used to obtain vap H. For Langmuir (i.e. nonequilibrium) vaporization, an activation barrier to vaporization due to the IL-gas surface structure could exist.…”

Crystallization and Glass-Forming Ability of Ionic Liquids: Novel Insights into Their Thermal Behavior

“…However, most of the work reported until now is mainly related to imidazolium- or pyridinium-based ILs combined with [Cl] − , [BF 4 ] − , [PF 6 ] − , or [NTf 2 ] − . − Despite of the intense research, many data found in the literature are not of the highest quality due to the use of different experimental methodologies (e.g., scanning rates, annealing periods, sample size, thermal history, and sample purity). − It is well accepted that ILs are structured fluids due to the complexity of their organization and diversity of the nature of their molecular interactions, showing high- and low-charge density regions. − The understanding of the nanostructuration of ILs and its intrinsic relation to most of their physicochemical properties is fundamental to achieve the possibility of tuning an ionic liquid to a specific functionality or application without endless screening and trial and error. The effects of nanostructuration have been detected in several physicochemical properties, such as heat capacities, ,− densities, surface tensions, , viscosities, ,− thermal behavior, ,,− and vapor pressures, − among others . For all these properties a trend shift was observed at the same critical value for the number of carbons of the alkyl chain N = 6, named as the critical alkyl size (CAS). ,,,,, Pyridinium based ILs have a high potential of applicability , due to their high thermal stability and the aromatic character of the cation, exhibiting physical-chemical properties very similar to those of the imidazolium cation analogues. − Nevertheless, the replacement of the imidazolium by the pyridinium cation modifies the structural organization of the liquid phase, affecting the physicochemical properties.…”