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This chapter reviews the state of the art in the syntheses, properties, and applications of fluorinated ionic liquids containing moieties with at least three fully fluorinated carbon atoms in their structure. The wide variety of synthetic strategies for the incorporation of fluorinated chains into the cation or anion of ionic liquids, and also the selected physicochemical properties of the resulting fluorinated ionic liquids, are reviewed. The applications of fluorinated ionic liquids that have been investigated by numerous research groups are also summarized, highlighting the main findings regarding their performances. Finally, the main benefits and drawbacks of the implementation of fluorinated ionic liquids in different processes are assessed and the best opportunities for future research on fluorinated ionic liquids are discussed.

The manuscript reports on a new class of aqueous biphasic systems (ABSs) formed in mixtures of inorganic salts (ISs) and zwitterionic salts (ZWSs). Aqueous ternary phase diagrams characterized by a binodal curve were determined for systems consisting of four ISs, K3PO4, K2HPO4, K2HPO4/KH2PO4, and K2CO3, and three structurally similar ZWSs differing in hydrophobicity. Comparison of phase behaviour of ABSs composed of ZWSs, ionic liquids (ILs) and zwitterions was provided. Potential of ZWSs based systems for extraction of aromatic molecules and amino acids, such as glycine, L-tryptophan, DL-phenylalanine, eugenol, and phenol was examined. Feasibility and limitations of isolation of products after partition and recovery of ZWS were discussed.

To facilitate potential applications of water-in-supercritical CO

The separation of small, hydrophilic molecules from aqueous solutions on one side and the dissolution of hydrophobic organic molecules in water on the other are nowadays among the most difficult challenges in chemical and bio-technology. Even though these two tasks are seemingly of opposite nature, it is demonstrated herein that both processes can be facilitated by addition of zwitterionic salts, a new class of compounds that can act either as a solubility enhancer or a phase-separation promoter depending on the structure of the solute dissolved in an aqueous solution. At a more fundamental level, this study investigates the salting in/out propensity of the ions and supports the importance of both salt-solute interaction and their concentration.

To facilitate potential applications of water-in-supercritical CO2 microemulsions (W/CO2 μEs)efficient and environmentally responsible surfactants are required with low levels fluorination. As wellas being able to stabilize water-CO2 interfaces, these surfactants must also be economical, prevent bioaccumulation and strong adhesion, deactivation of enzymes, and also be tolerant to high salt environments.Recently, an ion paired catanionic surfactant with environmentally-acceptable fluorinated C6-tails wasfound to be very effective at stabilizing W/CO2 μEs with high water-to-surfactant molar ratios (W0) up to~50 (Sagisaka, M. et al. Langmuir, 2019, 35, 3445–3454). As the cationic and anionic constituentsurfactants alone did not stabilize W/CO2 μEs, this was the first demonstration of surfactant synergisticeffects in W/CO2 microemulsions. The aim of this new study is to understand the origin of these intriguingeffects by detailed investigations of nanostructure in W/CO2 microemulsions using high pressure smallangle neutron scattering (HP-SANS). These HP-SANS experiments have been used to determine theheadgroup interfacial area and volume, aggregation number and effective packing parameter (EPP). TheseSANS data suggest the effectiveness of this surfactant originates from increased EPP and decreasedhydrophilic/CO2-philic balance, related to a reduced effective headgroup ionicity. This surfactant bearsseparate C6F13-tails and oppositely-charged headgroups, and was found to have a EPP value similar tothat of a double C4F9-tail anionic surfactant (4FG(EO)2), which was previously reported to be one of mostefficient stabilizers for W/CO2 μEs (maximum W0 = 60-80). Catanionic surfactants based on this newdesign will be key for generating super-efficient W/CO2 μEs with high stability and water solubilization.

This manuscript presents a comparative study of the physico-chemical behaviour of sulfobetaine-type single and double zwitterions and zwitterionic salts, and structurally similar mono- and di-cationic tetraalkylammonium salts in aqueous solutions. The study includes experimental determination of the density and viscosity of highly diluted aqueous solutions with derivation of the Jones-Dole viscosity B-coefficient, partial molal volumes at infinite dilution, and hydration numbers. The study also examines the effects of addition of the salts on the surface tension of cationic and anionic surfactants, upper critical solution temperature of a non-ionic surfactant, solubility of amino acids, and stability of a protein. The experimental investigation was performed taking a broad bottom-up approach with the aim to elucidate the effect of molecular architecture and charge (two versus four) on the degree of surface hydration of a molecule, kosmotropicity, and interactions with charged and hydrophilic/hydrophobic surfaces - all-important characteristics which define ability of a functional group to resist protein attachment. The novel multicharged zwitterionic materials have exhibited superior qualities, thus paving the way to development of a new platform in design of hydrophilic and anti-fouling surfaces by employing the four-charge bearing molecular motifs.

High-water-content water-in-supercritical CO2 (W/CO2) microemulsions are considered to be green, universal solvents, having both polar and nonpolar domains. Unfortunately, these systems generally require environmentally unacceptable stabilizers like long and/or multifluorocarbon-tail surfactants. Here, a series of catanionic surfactants having more environmentally friendly fluorinated C4-C6 tails have been studied in terms of interfacial properties, aggregation behavior, and solubilizing power in water and/or CO2. Surface tensions and critical micelle concentrations of these catanionic surfactants are, respectively, lowered by ∼9 mN/m and 100 times than those of the constituent single fluorocarbon-tail surfactants. Disklike micelles in water were observed above the respective critical micelle concentrations, implying the catanionic surfactants have a high critical packing parameter, which should be suitable for the formation of reverse micelles. Based on visual observation of phase behavior and Fourier transform infrared spectroscopic and small-angle neutron scattering studies, one of the three catanionic surfactants tested was found to form transparent single-phase W/CO2 microemulsions with a water-to-surfactant molar ratio of up to ∼50. This is the first successful demonstration of the formation of W/CO2 microemulsions by synergistic ion-pairing of anionic and cationic single-tail surfactants. This indicates that catanionic surfactants offer a promising approach to generate high-water-content W/CO2 microemulsions.

High-water-content water-in-supercritical CO

There have been many attempts to find suitable replacements for fluorinated surfactants due to problems related to their bioaccumulation and resistance to biodegradation. Meeting the exceptional performances of these compounds, however, remains largely an unaccomplished challenge. Currently, a solution might be found through the synthesis of new classes of fluorinated compounds that possess reduced environmental impact by following the recommended strategies for their greener and safer design. In this article we report a novel approach by designing a family of catanionic fluorinated surfactants that shows potential for improved degradation, good water solubility, and low Krafft points. Furthermore, these surfactants exhibit excellent fluorine efficiency and effectiveness of surface tension reduction.

Enhancing oil recovery from currently available reservoirs is a major issue for petroleum companies. Among the possible strategies towards this, chemical flooding through injection of surfactants into the wells seems to be particularly promising, thanks to their ability to reduce oil/water interfacial tension that promotes oil mobilization. Environmental concerns about the use of synthetic surfactants led to a growing interest in their replacement with surfactants of biological origin, such as lipopeptides and glycolipids produced by several microorganisms. Hydrophobins are small amphiphilic proteins produced by filamentous fungi with high surface activity and good emulsification properties, and may represent a novel sustainable tool for this purpose. We report here a thorough study of their stability and emulsifying performance towards a model hydrocarbon mixture, in conditions that mimic those of real oil reservoirs (high salinity and high temperature). Due to the moderate interfacial tension reduction induced in such conditions, the application of hydrophobins in enhanced oil recovery techniques does not appear feasible at the moment, at least in absence of co-surfactants. On the other hand, the obtained results showed the potential of hydrophobins in promoting the formation of a gel-like emulsion ‘barrier’ at the oil/water interface.

A series of ionic liquids based on Girard's reagents was synthesised. Their tunable thermomorphic behaviour with water was demonstrated, and slight modifications in the cationic structure led to drastic changes in their water miscibility. Their phase behaviour, involving monophasic–biphasic transitions, drove a number of practical applications, including scavenging water-soluble dyes and the extraction of metals from water.

The use of 5-phenyltetrazole, a bioisostere of benzoic acid, as an anion source to prepare an ionic liquid is described for the first time. Tetrabutylphosphonium 5-phenyltetrazolate undergoes phase separation from water with lower critical solution temperature phase behavior, in contrast to completely water miscibletetrabutylphosphonium benzoate, and also exhibits strong complexation with water with both eutectic and peritectic behavior that has not previously been observed in ionic liquid + water systems. The anhydrous and trihydrate salts were isolated and characterized by single crystal X-ray diffraction.

International audience; Zwitterionic salts are hybrid materials, incorporating some characteristics of zwitterions and of ionic liquids, e.g. numerous options for structural design and functionalisation. They are comprised of cations and anions in which an additional zwitterionic moiety is embedded into either the cation or the anion. Such materials are characterised by having extended polar domains and high hydrophilicity. Here, we present results from the study of novel zwitterionic salts that are representative examples of this class of materials and illustrate the potential to exploit their functionalities and high hydrophilicity.

It is often believed that both ionic liquids and surfactants generally behave as non-specific denaturants of proteins. In this paper, it is shown that amphiphilic ionic liquids bearing a long alkyl chain and a target molecule, where the target molecule is appended via a carboxylic ester functionality, can represent super-substrates that enable the catalytic activity of an enzyme, even at high concentrations in solution. Menthol has been chosen as the target molecule for slow and controlled fragrance delivery, and it was found that the rate of the menthol release can be controlled by the chemical structure of the ionic liquid. At a more fundamental level, this study offers an insight into the complex hydrophobic, electrostatic, and hydrogen bond interactions between the enzyme and substrate.

We present a study on the phase equilibrium behaviour of binary mixtures containing two 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide-based ionic liquids, [C(n)mim] [NTf(2)] (n=2 and 4), mixed with diethylamine or triethylamine as a function of temperature and composition using different experimental techniques. Based on this work, two systems showing an LCST and one system with a possible hourglass shape are measured. Their phase behaviours are then correlated and predicted by using Flory-Huggins equations and the UNIQUAC method implemented in Aspen. The potential of the COSMO-RS methodology to predict the phase equilibria was also tested for the binary systems studied. However, this methodology is unable to predict the trends obtained experimentally, limiting its use for systems involving amines in ionic liquids. The liquid-state structure of the binary mixture ([C(2)mim] [NTf(2)]+diethylamine) is also investigated by molecular dynamics simulation and neutron diffraction. Finally, the absorption of gaseous ethane by the ([C(2)mim][NTf(2)]+diethylamine) binary mixture is determined and compared with that observed in the pure solvents.

The melting temperatures of [Cnmpy]Cl (4 ≤ even n ≤ 18) were determined by a dynamic method and confirmed by differential scanning calorimetry. The latter technique was also used to measure the corresponding enthalpies of fusion. The temperatures marking the onset of decomposition of the eight ionic liquids were determined by thermogravimetry. The solid–liquid and liquid–liquid phase equilibria of binary mixtures of pyridine or nicotine with four ionic liquids of the 1-alkyl-3-methylpyridinium chloride family ([Cnmpy]Cl with n = 4, 6, 10, 16) were investigated. The T–x phase diagrams were measured at atmospheric pressure using turbidimetry in the (280 to 378) K temperature range. The diagrams show that pyridine is miscible in all proportions with the four studied ionic liquids while nicotine is only partially miscible with [C4mpy]Cl and [C6mpy]Cl. Data were interpreted using molecular dynamics simulations. The study illustrates, once again, the unique structural and solvent properties of ionic liquids.

We present a phenomenological approximation to the study of various non-universal features of liquid–liquid phase transitions in the framework of an approximate equation that relates the excess volume, the excess enthalpy, and the slope of the critical line. The mixtures under study are those containing 1-nitropropane (NP) or nitrobenzene (NB) and n-alkanes (CNH2N+2). The validity range of the above-mentioned equation is studied in detail for NP–CNH2N+2 systems. The consistency thus observed is within the experimental resolution limits, indicating that the equation can be extremely successful. The influence of effects at a molecular level on the slope of the critical line and on the critical amplitude of the isobaric thermal expansivity is analyzed from the microscopic interpretation of the excess volume and the excess enthalpy. This analysis is extended to NB–CNH2N+2 systems. The results reflect the importance of volumetric effects on critical behaviour, short-range anti-parallel ordering in NB appearing to be particularly relevant. © 2007 Elsevier B.V. All rights reserved.

The effects of the addition of three inorganic salts, namely, NaCl, Na(2)SO(4), and Na(3)PO(4), on the liquid-liquid (L-L) phase diagram of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], were investigated. All three inorganic salts trigger salting-out effects, leading to significant upward shifts of the L-L demixing temperatures of the systems. The magnitude of the shifts depends on both the water-structuring nature of the salt and its concentration; that is, the effects are correlated with the ionic strength of the solution and the Gibbs free energy of hydration of the inorganic salt. The pH effect and the occurrence of salt precipitation in concentrated solutions are also discussed.

This work presents new liquid–liquid equilibrium data for mixtures of 1H,1H,7H-perfluoroheptan-1-ol and linear perfluoroalkanes from C6 to C9. Data were measured at atmospheric pressure by turbidimetry and at pressures up to 5 MPa using a laser light scattering technique. The coexistence curves have been fitted to renormalization group extended-scaling expressions with the critical temperature and molar fraction obtained from the fit. The soft-SAFT equation of state (EoS) was also used to describe the experimental data at both low and high pressures. A good description of the immiscibility gap was obtained with this approach although results seem to deteriorate at high pressures showing that the model cannot simultaneously describe the equilibrium and excess thermodynamic properties.

Despite the structural similarity between perfluoroalkanes (PFCs) and alkanes (HCs), mixtures containing these two classes of compounds present large deviations from Raoult's law and extended immiscibility regions. The study of these mixtures is of great interest for both practical applications and testing or improving theories of mixtures as well as for the general understanding of solute–solvent interactions. In this work, new liquid–liquid equilibrium (LLE) data for mixtures of perfluoro-n-octane and linear alkanes from C6 to C9 are presented. Data were measured at atmospheric pressure by turbidimetry and at pressures up to 150 MPa using a laser light scattering technique. The binary liquid–liquid equilibrium data were correlated using relations derived from renormalization group (RG) theory and the Modified UNIFAC with temperature dependent interaction parameters. The soft-SAFT equation of state (EoS) was also used, with parameters taken from vapour–liquid equilibrium (VLE) data to study their transferability to liquid–liquid equilibrium data. It is shown that using those parameters soft-SAFT can provide a good description of the data measured far from the critical point at atmospheric pressure and a correct dependence of the critical temperature up to 150 MPa if the size interaction parameter is also considered.

The current study focuses on several phosphonium-based ionic liquids, namely, trihexyltetradecylphosphonium chloride, trihexyltetradecylphosphonium acetate, and trihexyltetradecylphosphonium bis{(trifluoromethyl)sulfonyl}amide. The objective was to study the influence of pressure as well as that of the anion on several properties of this type of ionic liquids. Densities in pure ionic liquids as a function of temperature and pressure have been determined. Other thermodynamic properties, such as the isothermal compressibility, the isobaric expansivity, and the thermal pressure coefficient, have been calculated. Density measurements have been performed at a broad range of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 65) using a vibrating tube densimeter. A simple ideal-volume model was employed for the prediction of the molar volumes of the phosphonia at ambient conditions, which proved to compare favorably with the experimental results.

We investigated the mutual solubility of mixtures of phosphonium-based ionic liquids with alkanes, alkanols, fluorinated alkanes and fluorinated alkanols. The solubilities of other solute molecules like water, formamide, 1,4-dioxane, benzene, and dimethylsulfoxide were also tested. Whenever possible, the corresponding temperature-composition (T-x) phase diagrams at atmospheric pressure were built from cloud-point temperature determinations. The influence of the size of the solute was tested with binary mixtures of trihexyl(tetradecyl)phosphonium acetate, [P(6 6 6 14)][Ac], with hexane, decane or tetradecane. The influence of the anion of the ionic liquid, namely acetate, [Ac], bis-[(trifluoromethyl)sulfonyl]imide, [Ntf(2)], trifluoromethanesulfonate, [Otf], and dicyanamide, [dca], on the solubility of the ionic liquids in hexane was also studied. For the ionic liquid [P(6 6 6 14)][Ntf(2)] the liquid-liquid phase diagrams were determined with different solutes-alkanes, perfluoroalkanes, partially fluorinated alkanes, and partially fluorinated alkanols-with the aim of analysing the solute-solvent interactions. A comparison of the phase behaviour of solutions containing phosphonium-based ionic liquids and 1-alkyl-3-methylimidazolium based ionic liquids, including a discussion of their different morphologies at a structural level, is also provided. It was found that fluorination of the aliphatic chains of organic compounds can be used as an effective way to control the solubility limits of these compounds in phosphonium- or imidazolium-based ionic liquids, both in terms of concentration and temperature.

This work extends the scope of previous studies on the phase behavior of mixtures of ionic liquids with benzenes or its derivatives by determining the solid-liquid and liquid-liquid phase diagrams of mixtures containing an ionic liquid and a fluorinated benzene. The systems studied include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide plus hexafluorobenzene or 1,3,5-trifluorobenzene and 1-ethyl-3-methylimidazolium triflate or N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide plus benzene. The phase diagrams exhibit different kinds of solid-liquid behavior: the (usual) occurrence of eutectic points; the (not-so-usual) presence of congruent melting points and the corresponding formation of inclusion crystals; or the observation of different ionic liquid crystalline phases (polymorphism). These different types of behavior can be controlled by temperature annealing during crystallization or by the nature of the aromatic compound and can be interpreted, at a molecular level, taking into account the structure of the crystals or liquid mixtures, together with the unique characteristics of ionic liquids, namely the dual nature of their interactions with aromatic compounds.

A set of 1-alkyl-3-methylimidazolium alkanesulfonate ionic liquids, [C(n)mim][C(k)SO(3)], formed by the variation of the alkyl chain lengths both in the cation and the anion (n = 1-6, 8, or 10; k = 1-4, or 6), was synthesised, with sixteen of them being novel. The ionic liquids were characterised by (1)H and (13)C NMR spectroscopy, and mass spectrometry. Their viscosities and densities as a function of temperature, as well as melting points and decomposition temperatures, were determined. The molecular volumes, both experimental and calculated, were found to depend linearly on the sum (n + k).

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.

Anionic and cationic alkyl-chain effects on the self-aggregation of both neat and aqueous solutions of 1-alkyl-3-methylimidazolium alkylsulfonate salts ([C(n)H(2n+1)mim][C(m)H(2m+1)SO(3)]; n = 8, 10 or 12; m = 1 and n = 4 or 8; m = 4 or 8) have been investigated. Some of these salts constitute a novel family of pure catanionic surfactants in aqueous solution. Examples of this class of materials are rare; they are distinct from both mixed cationic-anionic surfactants (obtained by mixing two salts) and gemini surfactants (with two or more amphiphilic groups bound by a covalent linker). Fluorescence spectroscopy and interfacial tension measurements have been used to determine critical micelle concentrations (CMCs), surface activity, and to compare the effects of the alkyl-substitution patterns in both the cation and anion on the surfactant properties of these salts. With relatively small methylsulfonate anions (n = 8, 10 and 12, m = 1), the salts behave as conventional single chain cationic surfactants, showing a decrease of the CMC upon increase of the alkyl chain length (n) in the cation. When the amphiphilic character is present in both the cation and anion (n = 4 and 8, m = 4 and 8), novel catanionic surfactants with CMC values lower than those of the corresponding cationic analogues, and which exhibited an unanticipated enhanced reduction of surface tension, were obtained. In addition, the thermotropic phase behaviour of [C(8)H(18)mim][C(8)H(18)SO(3)] (n = m = 8) was investigated using variable temperature X-ray scattering, polarising optical microscopy and differential scanning calorimetry; formation of a smectic liquid crystalline phase with a broad temperature range was observed.

In this work, we explore the mutual solubility of a number of mixtures of commonly used ionic liquids (imidazolium, pyridinium, phosphonium and ammonium ionic liquids) with partially fluorinated n-alcohols (C7 to C10) or perfluoroheptane. The corresponding T–x diagrams at atmospheric pressure were measured through cloud-point temperature determinations. For some selected systems under near-critical isopleth conditions, pressure effects were also studied. The results are discussed in terms of (i) shifts in the immiscibility envelopes as the cation alkyl-chain length is changed, (ii) the nature of the cation or the anion, (iii) the increasing length of the fluorinated/alkylic moiety of the partially fluorinated alcohol, or (iv) comparisons with similar systems involving normal alcohols.

Interfacial tension (using a drop-shape analysis technique), fluorescence (of a widely used spectroscopic molecular probe, pyrene), and 1H NMR measurements were used to monitor the adsorption at the aqueous solution–air interface and self-aggregation behaviour (critical micelle concentration, CMC) of room-temperature ionic liquids (ionic liquids) of the 1-alkyl-3-methylimidazolium family of cations, [Cnmim]+, with different linear alkyl chain lengths, CnH2n+1 (½n = 1–7), and different counter-ions, namely [Cnmim]Cl (n = 2–14), [Cnmim][PF6] (n = 4 or 10), and [C10mim][NTf2]. Only [Cnmim]Cl with n > 8 unambiguously form aggregates in solution and the nature of this self-aggregation is discussed in terms of the electrostatic vs. hydrophobic contributions of the isolated cation. In contrast, the shortest chains behave, as anticipated, as simple salts. In turn, the transitional ionic liquid, [C6mim]Cl is able to develop a monolayer at the aqueous solution–air interface but shows no noticeable self-aggregation in the bulk fluid. Moreover, the micellar characteristics of the well-studied sodium dodecyl sulfate (SDS) aqueous solutions as a function of the total concentration of [Cnmim]Cl (½n = 1–7) showed a clear change in the behaviour of the mixtures [Cnmim]Cl + SDS for n ≈ 6–8, with a characteristic mixed-micelle formation for the longer and a pure salt effect for the shorter chain lengths of [Cnmim]Cl.