Understanding the Role of Cholinium Carboxylate Ionic Liquids in PEG-Based Aqueous Biphasic Systems

This work aims at exploring new sustainable separation processes based on ionic liquids. Aqueous biphasic systems (ABS) based on poly­(ethylene glycol) (PEG) with low molecular weight (600 and 4000 g mol^–1) and cholinium-based ionic liquids and salts containing anions derived from carboxylic acids (oxalate, malonate, succinate, l-malate, fumarate, glutarate and citrate), available in natural compounds, are here presented. Contrary to common ionic liquids, the cholinium-based ionic liquids used in this work are biodegradable, nontoxic, cheap, and simple to prepare, and PEG is also a cheap and nontoxic phase promoter agent. The data reported in this work allows novel insights into the phase splitting mechanism of these ABSs regarding the influence of alkyl chain length of the anion and the presence of substituent groups in the anion. The effect of PEG molecular weight in the ABS was also addressed. Furthermore, the possible application of these systems for the extraction/separation of antioxidants, namely, <i>tert</i>-butylhydroquinone (TBHQ), was evaluated

Gas Permeation Properties of Fluorinated Ionic Liquids

Despite the increasing amount of research in the ionic liquids field, there are still quite unexplored themes. That is the case of the fluorinated ionic liquids (FILs) family, here defined as ionic liquids with fluorine tags longer than four carbon atoms. In this work, gas permeation properties of two fluorinated ionic liquids, tetrabutylammonium heptadecafluorooctanesulfonate and 1-ethyl-3-methylpyridinium perfluorobutanesulfonate, were studied. For that purpose, supported liquid membranes of the fluorinated ionic liquids were prepared using a polymeric porous membrane as supporting material, and their gas permeation properties for 10 different gases at 294 K were measured using a time-lag apparatus. The results show that the gas solubility of these FILs is of the same order of magnitude as gas solubilities for previously tested fluorinated ionic liquids and that solute size plays a more important role on gas diffusivity than viscosity. The perfluorocarbons and carbon dioxide separation performances were evaluated, and the results show that 1-ethyl-3-methylpyridinium perfluorobutanesulfonate is a better candidate than tetrabutylammonium heptadecafluorooctanesulfonate for the gas separation processes tested in this work

Impact of Self-Aggregation on the Formation of Ionic-Liquid-Based Aqueous Biphasic Systems

This work reports on the systematic investigation of the influence of the cation alkyl side-chain length of 1-alkyl-3-methylimidazolium chloride ionic liquids ([C_<i>n</i>C₁im]­Cl, with <i>n</i> = 1–14), as well as the substitution of the most acidic hydrogen in the imidazolium core by a methyl group, in the formation of aqueous biphasic systems. Ternary phase diagrams, tie-lines, tie-line slopes, tie-line lengths, and critical points for the several systems (ionic liquid + water + K₃PO₄) were determined and reported at 298 K and atmospheric pressure. It is shown that the increase of the cation alkyl chain length enhances the formation of aqueous biphasic systems if alkyl chain lengths until the hexyl are considered. The results for longer alkyl side chains show, nevertheless, that the phenomenon is more complex than previously admitted and that the capacity of the ionic liquid to self-aggregate also governs its ability to phase separate. The effect of the alkyl side-chain length on the phase-forming ability of the studied systems was quantitatively evaluated based on their salting-out coefficients derived from a Setschenow-type behavior. The aptitude of each ionic liquid for liquid–liquid demixing as a function of the cation alkyl side-chain length clearly follows three different patterns. The results obtained for the trisubstituted cation indicate that the hydrogen-bonding interactions between the ionic liquid cation and water are not a relevant issue in the formation of aqueous two-phase systems. In general, for the [C_<i>n</i>C₁im]Cl series, a multifaceted ratio between entropic contributions and the ability of each ionic liquid to self-aggregate in aqueous media control the phase behavior

Influence of Nanosegregation on the Surface Tension of Fluorinated Ionic Liquids

We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ionic liquids (ILs) composed of 1-alkyl-3-methylimidazolium cations ([C_<i>n</i>C₁im] with <i>n</i> = 2, 4, 6, 8, 10, or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non-fluorinated ionic liquids. The most surprising and striking feature is the identification, for the first time, of a minimum at <i>n</i> = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamics (MD) simulations, it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) pointing toward the gas–liquid interface, a phenomenon which occurs in ILs with perfluorinated anions. Furthermore, these ILs present the lowest surface entropy reported to date

Liquid–Liquid Equilibrium of Cholinium-Derived Bistriflimide Ionic Liquids with Water and Octanol

The liquid–liquid equilibria of mixtures of cholinum-based ionic liquids (<i>N</i>-alkyl-<i>N,N</i>-dimethylhydroxyethylammonium bis­(trifluoromethane)­sulfonylimide, [N_{11<i>n</i>2OH}]­[Ntf₂], <i>n</i> = 1, 2, 3, 4, and 5) plus water or 1-octanol were investigated at atmospheric pressure over the entire composition range. The experiments were conducted between 265 and 385 K using the cloud-point method. The systems exhibit phase diagrams consistent with the existence of upper critical solution temperatures. The solubility of [N_{1 1 <i>n</i> 2OH}]­[Ntf₂] in water is lower for cations with longer alkyl side chains (larger <i>n</i> values). The corresponding trend in the octanol mixtures is reversed. The ([N_1 1 1 2OH]­[Ntf₂] + water + octanol) ternary system shows triple liquid–liquid immiscibility at room temperature and atmospheric pressure. A combined analytic/synthetic method was used to estimate the corresponding phase diagram under those conditions. Auxiliary molecular dynamics simulation data were used to interpret the experimental results at a molecular level

Systematic Study of the Thermophysical Properties of Imidazolium-Based Ionic Liquids with Cyano-Functionalized Anions

In the past few years, ionic liquids (ILs) with cyano-functionalized anions have shown to be improved candidates for electrochemical and separation applications. Nevertheless, only scattered data exist hitherto and a broad analysis of their structure–property relationship has yet to be attempted. Therefore, in this work, a systematic study of the densities, viscosities and refractive indices of imidazolium-based ILs with cyano-functionalized anions was carried out at 0.1 MPa within a broad temperature range (from 278 to 363 K). The ILs under study are based on 1-alkyl-3-methylimidazolium cations (alkyl = ethyl, butyl and hexyl) combined with the [SCN]⁻, [N­(CN)₂]⁻, [C­(CN)₃]⁻ and [B­(CN)₄]⁻ anions. The selected matrix of cation/anion combinations allows us to provide a detailed and comprehensive investigation of the influence of the −CN group through an analysis of the thermophysical properties of the related ILs. The results show that, regardless of the cation, the densities decrease with an increase in the number of cyano groups or anion molecular weight. Moreover, for a fixed cation and temperature, the refractive index of the ILs decreases according to the rank: [SCN]⁻ > [N­(CN)₂]⁻ ≈ [C­(CN)₃]⁻ > [B­(CN)₄]⁻. On the other hand, no clear trend was observed for the viscosity of ILs and the respective number of −CN groups. The viscosity dependence on the cyano-functionalized anions decreases in the order: [SCN]⁻ > [B­(CN)₄]⁻ > [N­(CN)₂]⁻ > [C­(CN)₃]⁻. The isobaric thermal expansion coefficient, the derived molar refraction, the free volume, and the viscosity energy barrier of all compounds were estimated from the experimental data and are presented and discussed. Finally, group contribution models were applied, and new group contribution parameters are presented, extending these methods to the prediction of the ILs properties

Influence of Nanosegregation on the Phase Behavior of Fluorinated Ionic Liquids

Fluorinated ionic liquids (FILs) have received increasing attention due to their physicochemical properties. They allow us to enlarge the tuneability power of traditional ionic liquids. With the aim to understand the thermodynamic behavior of these compounds, a study of solid–fluid transitions using differential scanning calorimetry, thermogravimetric analysis, rheology, and molecular dynamics simulation has been performed. A comparison between different cations, anions, and hydrogenated alkyl chains was carried out using ionic liquids with fluorinated alkyl chain lengths equal to or longer than four carbon atoms. In this work, we provide evidence of the fluorinated domain influence on the thermodynamic behavior of these compounds. Moreover, the results suggest that the nanosegregation of the fluorous domains might be an interesting structural feature that modifies and/or enhances the rich phase behavior of the FILs, increasing the probability of these compounds to adopt different conformations. This information is crucial to design the best FIL and can increase their potential on a wide range of applications

Ex Situ Reconstitution of the Plant Biopolyester Suberin as a Film

Biopolymers often have unique properties of considerable interest as a basis for new materials. It is however not evident how to extract them from plants without destroying their chemical skeleton and inherent properties. Here we report the ex situ reconstitution of the biopolyester suberin as a new waterproof and antimicrobial material. In plant cell walls, suberin, a cross-linked network of aromatic and aliphatic monomers, builds up a hydrophobic protective and antimicrobial barrier. Recently we succeeded in extracting suberin from the plant cell wall using the ionic liquid cholinium hexanoate. During extraction the native three-dimensional structure of suberin was partially preserved. In this study, we demonstrate that this preservation is the key for its ex situ reconstitution. Without any chemical additives or purification, the suberin composing macromolecules undergo self-association on the casting surface forming a film. Suberin films obtained show barrier properties similar to those of the suberin barrier in plants, including a potentially broad bactericidal effect