Probing the effects of the ester functional group, alkyl side chain length and anions on the bulk nanostructure of ionic liquids: a computational study

Abstract

The effects of ester addition on nanostructural properties of biodegradable ILs composed of 1-alkoxycarbonyl-3-alkyl-imidazolium cations ([C1COOCnC1im](+), n = 1, 2, 4) combined with [Br](-), [NO3](-), [BF4](-), [PF6](-), [TfO](-), and [Tf2N](-) were explored by using the molecular dynamics (MD) simulations and quantum theory of atoms in molecules (QTAIM) analysis at 400 K. Various thermodynamic properties of these ILs were extensively computed in our earlier work (Ind. Eng. Chem. Res., 2015, 54, 11678-11700). Nano-scale segregation analysis demonstrates the formation of a small spherical island-like hydrocarbon within the continuous ionic domain for ILs with short alkyl side chain ([C1COOC1C1im]), and a sponge-like nanostructure for the compound with long alkyl side chain ([C1COOC4C1im]). Ester-functionalized ILs with ethyl side chain ([C1COOC2C1im]) are the turning point between two different morphologies. Non-polar channels were observed for [C1COOC4C1im] ILs composed of smaller anions such as [Br] and [NO3], whereas clustering organization was found for the other anions. Formation of the spherical micelle-like nanostructure was seen for lengthened cations. Finally, the incorporation of an ester group into the alkyl side chain of the cation leads to stronger segregation between charged and uncharged networks, which consequently increased the possibility of self-assembly and micelle formation.

Effect of Anion and Alkyl Side Chain on Structural and Dynamic Features of Ester Functionalized Ionic Liquids: Confirming Nanoscale Organization

“…3 The basis set superposition errors (BSSE) are eliminated using the counterpoise method (CP). 20 S4), which is in excellent agreement with the obtained results of the isolated ion pair (from ab initio calculations) 3 and average structures of cations (from MD simulations) 17 in our previous studies.…”

“…19 The details of performed MD simulations as well as force field parameters were illustrated in the Supporting Information. It should be emphasized that the equilibrated simulation systems at 400 K from 1.5 ns simulations in our previous work 17 were implemented as starting configurations in this study. To reach the self-diffusivity regime, long-time simulations (5 ns) were carried out for all selected ILs.…”

“…These intramolecular H bonds were previously revealed from the torsion energy profile of the C 5 −N−C 6 −C 7 dihedral, 3 optimized struc-tures of isolated ion pair, 3 and also the average structures of cations from MD simulations. 17 Furthermore, the different kinds of regions can be shown via a scatter graph (Figures S6−S8 of the Supporting Information). There are three kinds of spikes in scatter graph, which can be classified into three types.…”

“…Hence, the main aim of the present work is to investigate the structural and dynamic properties of ester functionalized ILs composed of 3-methyl-1- Figure S1 indicates the ball and stick model of selected ILs. Thermodynamic properties 3 and self-assembly behavior 17 of these ILs were extensively studied in our earlier work.…”

Voronoi Polyhedra as a Tool for the Characterization of Inhomogeneous Distribution in 1-Butyl-3-methylimidazolium Cation-Based Ionic Liquids

“…This induces a sort of charge-ordering at the level of the local structure. This heterogeneity creates inherent interfaces, which should influence the solvation process in such media. ,− Indeed, the solvation of a solute depends strongly on its preferential localization in these different regions of the IL (i.e., within the polar network, in the nonpolar domains, or at the interface between the polar and nonpolar domains) …”