José N. Canongia Lopes

The distillation and volatility of ionic liquids

It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200–300 °C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

Aqueous biphasic systems: a boost brought about by using ionic liquids

During the past decade, ionic-liquid-based Aqueous Biphasic Systems (ABS) have been the focus of a significant amount of research. Based on a compilation and analysis of the data hitherto reported, this critical review provides a judicious assessment of the available literature on the subject. We evaluate the quality of the data and establish the main drawbacks found in the literature. We discuss the main issues which govern the phase behaviour of ionic-liquid-based ABS, and we highlight future challenges to the field. In particular, the effect of the ionic liquid structure and the various types of salting-out agents (inorganic or organic salts, amino acids and carbohydrates) on the phase equilibria of ABS is discussed, as well as the influence of secondary parameters such as temperature and pH. More recent approaches using ionic liquids as additives or as replacements for common salts in polymer-based ABS are also presented and discussed to emphasize the expanding number of aqueous two-phase systems that can actually be obtained. Finally, we address two of the main applications of ionic liquid-based ABS: extraction of biomolecules and other added-value compounds, and their use as alternative approaches for removing and recovering ionic liquids from aqueous media.

Molecular Force Field for Ionic Liquids IV: Trialkylimidazolium and Alkoxycarbonyl-Imidazolium Cations; Alkylsulfonate and Alkylsulfate Anions

This is the fourth article of a series that describes the parametrization of a force field for the molecular simulation of common ionic liquids within the framework of statistical mechanics. The force field was developed in the spirit of the OPLS-AA model and is thus oriented toward the calculation of equilibrium thermodynamic and structural properties in the condensed (liquid) phase. The ions modeled in the present paper are cations of the 1,2,3-trialkylimidazolium and alkoxycarbonyl imidazolium families and alkylsulfate and alkylsulfonate anions. As in previous publications, the force field is built in a stepwise manner that allows, for example, the construction of models for an entire family of cations or anions, with alkyl side chains of different length. Because of the transferability of the present force field, the ions studied here can be combined with those reported in our three previous publications to create a large variety of ionic liquids that can be studied by molecular simulation. The extension of the force field was validated by comparison of simulation results with the corresponding crystal structure and liquid density experimental data.

High-Accuracy Vapor Pressure Data of the Extended [CnC1im][Ntf2] Ionic Liquid Series: Trend Changes and Structural Shifts

For the first time, two distinct trends are clearly evidenced for the enthalpies and entropies of vaporization along the [Cnmim][Ntf2] ILs series. The trend shifts observed for Δ(l)(g)H(m)(o) and Δ(l)(g)S(m)(o), which occur at [C6mim][Ntf2], are related to structural modifications. The thermodynamic results reported in the present article constitute the first quantitative experimental evidence of the structural percolation phenomenon and make a significant contribution to better understanding of the relationship among cohesive energies, volatilities, and liquid structures of ionic liquids. A new Knudsen effusion apparatus, combined with a quartz crystal microbalance, was used for the high-accuracy volatility study of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series ([Cnmim][Ntf2], where n = 2, 3, 4, 5, 6, 7, 8, 10, 12). Vapor pressures in the (450–500) K temperature range were measured, and the molar standard enthalpies, entropies, and Gibbs energies of vaporization were derived. The thermodynamic parameters of vaporization were reported, along with molecular dynamic simulations of the liquid phase structure, allowing the establishment of a link between the thermodynamic properties and the percolation phenomenon in ILs.

High-performance extraction of alkaloids using aqueous two-phase systems with ionic liquids

Ionic-liquid-based aqueous two-phase systems are great candidates for the replacement of volatile organic compounds in typical liquid–liquid extractions. This work shows clear evidence for the complete extraction of alkaloids such as caffeine and nicotine using a single-step procedure.

Structure and Aggregation in the 1-Alkyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid Homologous Series

A new comprehensive Molecular Dynamics study using large simulation boxes has been performed in order to complete and extend the structural analysis on the mesoscopic segregation observed in the ionic liquids of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide homologous series, [CnC1im][Ntf2] (2 ≤ n ≤ 10). The analysis includes the discussion along the whole family of the corresponding structure factors, S(q), in the low-q range (1.6 ≤ q/nm(-1) ≤ 20); the confirmation of the periodicity of the polar network of the ionic liquid and its intermediate low-q peak equivalence; and the introduction of five statistical functions that probe the existence and characterize the polar network and the nonpolar aggregates that are formed along the [CnC1im][Ntf2] series. The later functions comprise aggregate size distributions, average number of contact neighbors within an aggregate, neighbor distributions, distributions of aggregate maximum length, and distributions of aggregate volume.

On the self-aggregation and fluorescence quenching aptitude of surfactant ionic liquids.

The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and (1)H NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [Cnmpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n=4, 10, 12, 14, 16, or 18), [C12mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C12mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C12mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established.

Three commentaries on the nano-segregated structure of ionic liquids

Abstract The concept that ionic liquids are nano-segregated fluids has allowed the rationalization at a molecular level of many of their complex and unusual properties, either as pure substances or as solvents. In this work we will use molecular dynamics simulation results to discuss in a semi-quantitative manner different aspects of such segregation: how it varies within a homologous ionic liquid family; the influence of the nature of the ions in the morphology of the segregated domains; and the interactions of those domains with molecular solutes or solvents.

CL&P: A generic and systematic force field for ionic liquids modeling

In this account, we review the process that led to the development of one of the most widely used force fields in the area of ionic liquids modeling, analyze its subsequent expansions and alternative models, and consider future routes of improvement to overcome present limitations. This includes the description and discussion of (1) the rationale behind the generic and systematic character of the Canongia Lopes & Padua (CL&P) force field, namely its built-in specifications of internal consistency, transferability, and compatibility; (2) the families of ionic liquids that have been (and continue to be) parameterized over the years and those that are the most challenging both in theoretical and applied terms; (3) the steps that lead to a correct parameterization of each type of ion and its homologous family, with special emphasis on the correct modeling of their flexibility and charge distribution; (4) the validation processes of the CL&P and other force fields; and finally (5) the compromises that have to be attained when choosing between generic or specific force fields, coarse-grain or atomistic models, and polarizable or non-polarizable methods. The application of the CL&P and other force fields to the study of ionic liquids using quantum- and statistical-mechanics methods has led to the discovery and analysis of the unique nature of their liquid phases, that is, the notion that ionic liquids are nano-segregated fluids with structural and dynamic heterogeneities at the nanoscopic scale. This successful contribution of theoretical chemistry to the field of ionic liquids will also serve as a guide throughout the ensuing discussion.

The Structure of Aqueous Solutions of a Hydrophilic Ionic Liquid: The Full Concentration Range of 1-Ethyl-3-methylimidazolium Ethylsulfate and Water

Several structural features of aqueous solutions of the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate were analyzed in the entire concentration range using molecular dynamics simulation results. Different analysis tools developed in-house were applied to describe the size and connectivity of different water and ion aggregates as a function of the solution concentration. Four concentration ranges-x(H(2)O)<0.5, 0.50.95-with four distinct structural regimes--isolated water molecules, chain-like water aggregates, bicontinuous system, and isolated ions or small ion clusters--were identified and discussed, including two different percolation limits: that of water in the ionic liquid network (around x(H(2)O)=0.8) and that of the ionic liquid in water (around x(H(2)O)=0.95).