Further development of the predictive models for physical properties of pure ionic liquids: Thermal conductivity and heat capacity

Abstract

Efficient, fast and accurate heat transfer units design is currently a 'hot topic' due to the demand for more approachable and high-performance-ability materials. This is usually performed by the prediction of physical properties coupled with sufficient structure searching (for example with genetic algorithm). Ionic liquids have been found to be prospective replacement materials in this case; however, the predictive capabilities of existing models still remain poor which affects their practical application significantly. It has also been observed that for some quaternary-phosphonium based carboxylate ILs, the models fail, particularly, for thermal conductivity and heat capacity predictions. The impact of electronic structure on the heat capacity was confirmed by DFT calculations, and this was also included in further refinement. The aim of this work is to assess the predictive capabilities of existing models for thermal conductivity and heat capacity, with further improvements based on more accurate investigated structure characterization (DFT) and reparameterization (group contribution methodology). The ILs chosen for the initial study are trihexyl(tetradecyl)phosphonium-based carboxylate derivatives.

Synthesis, NMR, Raman, thermal and nonlinear optical properties of dicationic ionic liquids from experimental and theoretical studies

“…In present work, HOMO orbital of bisImPF 6 is delocalised in the imidazolium ring segment and not in the PF 6 .Supported by previously reported work [69]. From these analyses, it can be said that it is reasonable to assume that the imidazolium ring in the case of the bisImPF 6 DIL acts as the main site to donate electrons.…”

“…As shown in Figure 6, the symmetric modes at 2817 and 2876 cm -1 in bisImCl and at 2844 and 2895 cm -1 for bisImPF 6 were assigned to the methyl group attached to the imidazolium rings N + -(CH 3 ) [27,47]. The bands at 2948, 2981 , 2989 cm -1 for bisImCl and at 2965, 2981, 3007 cm -1 for bisImPF 6 corresponding to the methylene group (-CH 2 -) [27]. While, the anti-symmetric modes of methyl group N + -(CH 3 ) attached to the imidazolium rings appeared at 3013, 3029, 3043 cm -1 for bisImCl and at 3023, 3046 cm -1 for bisImPF 6.…”

“…Optimized structures of BisIm cation, and ionic liquids BisImCl and BisImPF 6 in gas phase by using B3LYP/6-311++G** calculations can be easily seen in Figure 1 while in Figure 2 are shown the intermolecular cations-anions contacts by using the same level of theory with In Table 1 are summarized calculated and corrected by ZPVE total energies, dipole moments and volumes of cation and ionic liquids bisImCl and bisImPF 6 in gas phase by using B3LYP/6-311++G** calculations. The ionic liquid bisImCl presents the higher dipole moment value probably due to great size of Cl atoms while the higher volume is observed for bisImPF 6 . Note that the energies values have lower values when they are corrected by ZPVE, as also was observed in the ionic liquid 1-Ethyl-3-methylimidazolium hexafluorophosphate [37].…”

“…For both bisImCl and bisImPF 6 the corresponding molecular graphics in gas phase by using B3LYP/6-311++G** calculations are given in Figures 3 and 4, respectively. bisImPF 6 , as compared with bisImCl due to high number of H bonds interactions.…”

“…Imidazolium-based ILs are very popular due to their chemical and thermal stability, wellestablished structural characterization, low viscosity, and their widespread potential applications [4,5]. For example, varying the substituents of the imidazolium ring drastically changes the physical properties of these ILs [6]. The attractive and potentially tunable properties of these fascinating materials make them not just replacements for conventional…”