Nanostructured solvation in mixtures of protic ionic liquids and long-chained alcohols

Abstract

The structural and dynamical properties of bulk mixtures of long-chained primary and secondary alcohols (propanol, butanol, and 2-pentanol) with protic ionic liquids (ethylammonium and butylammonium nitrate) were studied by means of molecular dynamics simulations and small angle X-ray scattering (SAXS). Changes in the structure with the alcohol concentration and with the alkyl chain length of the alcohol moieties were found, showing variations in the radial distribution function and in the number of hydrogen bonds in the bulk liquids. Moreover, the structural behaviour of the studied mixtures is further clarified with the spatial distribution functions. The global picture in the local scale is in good agreement with the nanostructured solvation paradigm [T. Méndez-Morales et al. Phys. Chem. B 118, 761 (2014)], according to which alcohols are accommodated into the hydrogen bonds' network of the ionic liquid instead of forming clusters in the bulk. Indeed, our study reveals that the alcohol molecules are placed with their polar heads at the interfaces between polar and nonpolar nanodomains in the ionic liquid, with their alkyl chains inside the nonpolar organic nanodomains. The influence of alcohol chain length in the single-particle dynamics of the mixtures is also reported calculating the velocity autocorrelation function and vibrational densities of states of the different species in the ionic liquid-alcohol mixtures, and a weak caging effect for the ethylammonium cations independent of the chain size of the alcohols was found. However, the SAXS data collected for the studied mixtures show an excess of the scattering intensities which indicates that there are also some structural heterogeneities at the nanoscale.

A Brief Guide to the Structure of High-Temperature Molten Salts and Key Aspects Making Them Different from Their Low-Temperature Relatives, the Ionic Liquids

“…In the early 2010s, there was significant controversy regarding the origin of the prepeak in ILs. ,,− In hindsight, and for prototypical ILs, this problem is very simple and has been fully resolved. ,,,,− For ILs, where cations have a charged head and a significantly large apolar tail, the prepeak is due to the typical distance between charge networks alternated by apolar regions, or apolar domains alternated by the charge network. − Since this is a pattern of alternation, same type species (polar–polar and apolar–apolar) show peaks in partial subcomponents of S ( q ) at the prepeak region, whereas opposite type species (polar–apolar) show an antipeak; notice that positive and negative species are considered “same type species” in this q regime because they are both polar. , This is clearly depicted in Figure , where polar cationic and anionic heads form networks that are separated by other networks via tails that act as spacers.…”

Insights on the mixtures of imidazolium based ionic liquids with molecular solvents

“…These characteristics determine the properties and structure of pure ILs but also have a large effect when mixing with molecular solvents (MSs) [4][5][6][7]. Intermolecular forces between ILs and MSs are largely complex [810], even with the appearance of competition effects between the involved ions and molecules [11], because of their dependence on the protic or aprotic, polar or apolar, or hydrogen bonding ability of the MSs, and show remarkable changes with mixture composition, pressure and temperature [12][13][14][15]. These mechanisms of ILs-MSs interactions determine the macroscopic physicochemical properties of mixed fluids [1618], and thus, their possible application for several technologies at industrial level [1921].…”

Hydrogen Bond Kinetics, Ionic Dynamics, and Voids in the Binary Mixtures of Protic Ionic Liquids with Alkanolamines

“…The abovementioned observations support the "solvation paradigm," which was discussed in the previous literature. 44,69 The neutral molecules present in the mixtures of ILs replace some of the cations around the anion. The AN RDFs have lower peak heights than CN RDFs.…”

“…The abovementioned results support the "solvation paradigm" proposed in previous studies. 44,69 The neutral molecules occupy the positions of the cation. The neutral molecules associate more in NICcontaining mixtures than SULF.…”