Evidence of a Phase Transition in Water−1-Butyl-3-methylimidazolium Tetrafluoroborate and Water−1-Butyl-2,3-dimethylimidazolium Tetrafluoroborate Mixtures at 298 K: Determination of the Surface Thermal Coefficient, bT,P

Evolution of Surface Tension and Hansen Parameters of a Homologous Series of Imidazolium-Based Ionic Liquids

In this study, we systematically analyze the surface tension and Hansen solubility parameters (HSPs) of imidazolium-based ionic liquids (ILs) with different anions ([NTf2]-, [PF6]-, [I]-, and [Br]-). These anions are combined with the classical 1-alkyl-3-methyl-substituted imidazolium cations ([CnC1Im]+) and a group of oligoether-functionalized imidazolium cations ([(mPEGn)2Im]+) based on methylated polyethylene glycol (mPEGn). In detail, the influences of the length of the alkyl- and the mPEGn-chain, the anion size, and the water content are investigated experimentally. For [CnC1Im]+-based ILs, the surface tension decreases with increasing alkyl chain length in all cases, but the magnitude of this decrease depends on the size of the anion ([NTf2]- < [PF6]- < [Br]- ≤ [I]-). Molecular dynamics (MD) simulations on [CnC1Im]+-based ILs indicate that these differences are caused by the interplay of charged and uncharged domains, in particular in the different anions, which affects the ability of the alkyl chains of the cation to orient toward the liquid-gas interface. An increase in the mPEGn-chain length of the [(mPEGn)2Im][A] ILs does not significantly influence the surface tension. These changes upon variation of the cation/anion combination do not correlate with the evolution of the HSPs for the two sets of ILs. Finally, our data suggest that significant water contents up to water mole fractions of x(H2O) = 0.25 do not significantly affect the surface tension of the studied binary IL-water mixtures.

Preparation of mesoporous ZnAl2O4 nanoflakes by ion exchange from a Na-dawsonite parent material in the presence of an ionic liquid

Herein, mesoporous ZnAl₂O₄ spinel nanoflakes were prepared by an ion-exchange method from a Na-dawsonite parent material in the presence of an ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride ([bdmim][Cl]), followed by calcination at 700 °C for 2 h. The as-obtained products were characterized by several techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The ZnAl₂O₄ nanoflakes with the thickness of ∼20 nm were composed of numerous nanoparticles, which resulted in a high specific surface area of 245 m² g⁻¹. The formation mechanism of the ZnAl₂O₄ nanoflakes was comprehensively investigated, and the results showed that a 2D growth process of the Zn₆Al₂(OH)₁₆(CO₃)·4H₂O crystallites with the assistance of [bdmim][Cl] was the key for the induction of ZnAl₂O₄ nanoflakes. Moreover, mesopores were formed between adjacent nanoparticles due to the release of CO₂ and H₂O molecules from Zn₆Al₂(OH)₁₆(CO₃)·4H₂O during the calcination process.

Herein, mesoporous ZnAl₂O₄ spinel nanoflakes were prepared by an ion-exchange method from a Na-dawsonite parent material in the presence of an ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride ([bdmim][Cl]), followed by calcination at 700 °C for 2 h.

Water Nanocluster Formation in the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate ([C4mim][BF4])-D2O Mixtures

The microstructure of mixtures of deuterated water in the ionic liquid [C4mim][BF4] is investigated by small-angle neutron scattering (SANS) measurement. In the salt-rich region, water dissolves in the ionic liquid up to 0.7 mole fraction, whereupon distinct, nanometer-sized water clusters are observed. These water nanoclusters increase in size with increasing water addition while the mole ratio of water dissolved into the ionic liquid nanostructure increases from 2 to 4. These results provide direct confirmation for recent simulations as well insight into the source of nonidealities in some thermophysical and transport properties (e.g., density and viscosity) of salt-rich aqueous mixtures reported in the literature.

Wettability alteration: A comprehensive review of materials/methods and testing the selected ones on heavy-oil containing oil-wet systems

Changing the wetting state of materials is a growing field of research in many areas of engineering and science. In the oil industry, the term wettability alteration usually refers to the process of making the reservoir rock more water-wet. This is of particular importance in naturally hydrophobic carbonates, fractured formations, and heavy-oil systems. This shift in wettability enhances oil recovery in oil-wet and weakly water-wet reservoirs and eventually increases the ultimate oil recovery. For wettability alteration, two methods have been traditionally used: Thermal and chemical. Although many attempts have been made on reviewing the advancement of research in certain aspects of wettability, a comprehensive review of these techniques, especially in terms of the classification of the chemicals used, has been ignored. In this paper, we begin with this review and provide the past experience of wettability alteration in sandstone and carbonate reservoirs. More than 100 papers were reviewed extensively with an in-depth analysis of different methods suggested in literature. The areas of controversy and contradicted observations are discussed. The limitations and the applicability of each method were analyzed. Concerns on up-scaling laboratory findings to field scale are also addressed. The most promising potential methods are identified and their critical conditions highlighted. At the end, a selection of reviewed methods is validated experimentally for one of the most challenging cases: Extra heavy-oil and bitumen recovery from fractured-strongly-oil-wet carbonates. Berea sandstone (aged to be oil-wet) and Indiana limestone samples were saturated with heavy oil (3600cp). Next, the process was initiated by soaking the cores into solvent (heptane or diluent oil) and the oil recovery was estimated using refractive index measurements. Note that solvent was selected to dilute the oil and recover a considerable amount of oil as any chemical or thermal methods yielded inefficiently low recoveries. After the solvent phase, the samples were exposed to wettability alteration through selected chemicals at different temperature conditions through spontaneous imbibition tests to recover more oil and retrieve the solvent diffuse into the sample back. The most promising wettability alteration agents for each type of rock were marked and optimal application conditions (temperatures, injection sequence) were identified. Selected wettability alteration chemicals were finally tested on the bitumen (5-9° API-1,600,000cp) containing Grosmont carbonate sample from Alberta, Canada. It is hoped that this review fills in the gap in the area of wettability alteration processes by summarizing, critically analyzing, and testing the methods suggested in the literature.

Pyridine derivatives; new efficient additives in bromide/tribromide electrolyte for dye sensitized solar cells

Propyl isonicotinate (PIN) and isopropyl isonicotinate (IPIN), have been synthesized through a simple and low cost method and for the first time, they have been applied as effective additives in bromide/tibromide electrolyte in DSSC.

Molecular dynamics investigation of the vibrational spectroscopy of isolated water in an ionic liquid

Experimental studies examining the structure and dynamics of water in ionic liquids (ILs) have revealed local ion rearrangements that occur an order of magnitude faster than complete randomization of the liquid structure. Simulations of an isolated water molecule embedded in 1-butyl-3-methyl imidazolium hexafluorophosphate, [bmim][PF6], were performed to shed insight into the nature of these coupled water-ion dynamics. The theoretical calculations of the spectral diffusion dynamics and the infrared absorption spectra of the OD stretch of isolated HOD in [bmim][PF6] agree well with experiment. The infrared absorption line shape of the OD stretch is narrower and blue-shifted in the IL compared to those in aqueous solution. Decomposition of the OD frequency time correlation function revealed that translational motions of the anions dominate the spectral diffusion dynamics.

Micellization of sodium laurylethoxysulfate (SLES) and short chain imidazolium ionic liquids in aqueous solution

In the present study the interactions between an anionic surfactant sodium laurylethoxysulfate (SLES) and three short chain imidazolium (1-butyl-3-methylimidazolium) based ionic liquids (bmim-octyl SO4, bmim-methyl SO4 and bmim-BF4) in aqueous solution have been investigated. Generally when a surfactant is dissolved in a hydrophilic ionic liquid aqueous solution the critical micelle concentration (cmc) obtained is attributed to the surfactant because the ionic liquid (IL) is considered to be only a cosolvent. However, some short hydrophilic ionic liquids posses surface activity in aqueous solution and behave like a surfactant. In that case mixed aggregates between surfactant and ionic liquid can be formed. The three SLES/IL systems here studied have been treated as typical binary surfactant mixtures in aqueous solution. Surface tension measurements have revealed that mixed aggregates and monolayers of surfactant and ionic liquid instead of single surfactant are responsible for the surface active properties of these aqueous solutions. From the Regular Solution Theory, negative interaction parameters (β) for mixed aggregates and monolayers have been found for all SLES/IL mole ratios indicating synergism between the anionic surfactant and the ionic liquids.

Interaction of nonionic surfactants and hydrophilic ionic liquids in aqueous solutions: can short ionic liquids be more than a solvent?

The interaction between an ethoxylated nonionic surfactant (C(12-14)EO(8)) and three conventional hydrophilic imidazolium-based ionic liquids (bmim-octyl SO(4), bmim-methyl SO(4), and bmim-BF(4)) in aqueous solution has been investigated. In most of the reported studies where a surfactant is dissolved in an ionic liquid aqueous solution, conventional ionic liquids are merely considered to be solvents. Consequently, the resulting critical micelle concentration (cmc) is considered to be that of the surfactant. However, given that the three ionic liquids selected showed the typical shape of a surface-active compound when the surface tension was plotted against concentration, the role of these compounds as secondary surfactants and consequently the possibility of mixed-micelle formation have been investigated. Different series of experiments where a surfactant and an ionic liquid were combined in a wide range of mole ratios have been performed and treated as typical binary surfactant systems in aqueous solution. It has been found for the three surfactant/ionic liquid systems that depending on the surfactant mole fraction, α(1), attractive or repulsive interactions in mixed-micelle formation are produced. Therefore, when we select the appropriate α(1) these systems can be adjusted to a given application, depending on whether monomers or micelles are mainly required.

Effect of temperature and cationic chain length on the physical properties of ammonium nitrate-based protic ionic liquids

We report a systematic study of the effect of the cationic chain length and degree of hydrogen bonding on several equilibrium and transport properties of the first members of the alkylammonium nitrate protic ionic liquids (PILs) family (ethylammonium, propylammonium, and butylammonium nitrate) in the temperature range between 10 and 40 °C. These properties were observed by means of several experimental techniques, including density, surface tension, refractometry, viscosimetry, and conductimetry. The dilatation coefficients and compressibilities, as well as the Rao coefficients, were calculated, and an increase of these magnitudes with alkyl chain length was detected. Moreover, the surface entropies and enthalpies of the studied PILs were analyzed, and the temperature dependence of the surface tension was observed to be describable by means of a harmonic oscillator model with surface energies and critical temperatures that are increasing functions of the cationic chain length. Moreover, the refractive indexes were measured and the thermo-optic coefficient and Abbe numbers were calculated, and the contribution of the electrostrictive part seemed to dominate the temperature dependence of the electric polarization. The electric conductivity and the viscosity were measured and the influence of the degree of hydrogen bonding in the supercooled liquid region analyzed. Hysteresis loops were detected in freezing-melting cycles and the effect of the length of the alkyl chain of the cation on the size of the loop analyzed, showing that longer chains lead to a narrowing of the supercooled region. The temperature dependence of the conductivity was studied in the Vogel-Fulcher-Tamman (VFT) framework and the fragility indices, the effective activation energies, and the Vogel temperatures obtained. A high-temperature Arrhenius analysis was also performed, and the activation energies of conductivity and viscosity were calculated, showing that these transport processes are governed by two distinct mechanisms. The exponents of the fractional Walden rule for the different compounds were obtained. Finally, the ionicities and fragilities of the studied PILs were analyzed, proving that all the studied PILs are subionic and fragile liquids, with propylammonium nitrate showing the lowest fragility and the greater ionicity of all the studied compounds.

Interactions between ionic liquid surfactant [C12mim]Br and DNA in dilute brine

Interactions between ionic liquid surfactant [C(12)mim]Br and DNA in dilute brine were investigated in terms of various experimental methods and molecular dynamics (MD) simulation. It was shown that the aggregation of [C(12)mim]Br on DNA chains is motivated not only by electrostatic attractions between DNA phosphate groups and [C(12)mim]Br headgroups but also by hydrophobic interactions among [C(12)mim]Br alkyl chains. Isothermal titration calorimetry analysis indicated that the [C(12)mim]Br aggregation in the presence and absence of DNA are both thermodynamically favored driven by enthalpy and entropy. DNA undergoes size transition and conformational change induced by [C(12)mim]Br, and the charges of DNA are neutralized by the added [C(12)mim]Br. Various microstructures were observed such as DNA with loose coil conformation in nature state, necklace-like structures, and compact spherical aggregates. MD simulation showed that the polyelectrolyte collapses upon the addition of oppositely charged surfactants and the aggregation of surfactants around the polyelectrolyte was reaffirmed. The simulation predicted the gradual neutralization of the negatively charged polyelectrolyte by the surfactant, consistent with the experimental results.

Surface tension of ionic liquids and ionic liquid solutions

Some of the most active scientific research fronts of the past decade are centered on ionic liquids. These fluids present characteristic surface behavior and distinctive trends of their surface tension versus temperature. One way to explore and understand their unique nature is to study their surface properties. This critical review analyses most of the surface tension data reported between 2001 and 2010 (187 references).

Aggregation Behavior of Imidazolium-Based Ionic Liquids in Water

The UV absorption spectra of aqueous solutions of [C4mim][Br], [C4mim][BF4], and [C8mim][Br], along with the differential UV spectra of aqueous [C8mim][Br] solutions, were measured at room temperature in this work. It is found that three transformations, denoted respectively as α, β and γ, can occur over the interested concentration range of solutions due to ionic liquid aggregation. Further, the content of ionic liquids and the wavelength of absorption maximum at these transformations are determined, and the implications at each transformation are analyzed. As a result, this paper discusses the effects of imidazolium cation, alkyl chain length and counterion type on the aggregation behavior and the contribution of interactions (such as hydrogen bonds, Coulombic, aliphatic and π–π stacking interactions) to the aggregation of 1-alkyl-3-methylimidazolium salts in water. Moreover, the possible structures of both aggregate and bulk phase in the aqueous solutions of ionic liquids are predicted also.

Insight into the Intermolecular Interactions in Ionic Liquid-Ethanol-Water Mixtures by Near-Infrared Spectroscopy

In this contribution, an insight into the interactions between 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and water/ethanol was offered using the Near-infrared (NIR) technique. It was found that the supermolecular structure of aqueous [Bmim]BF4 solution was destroyed as mole fraction of water surpasses 0.3979. The addition of ethanol is not favorable for water molecules to interacting with C2-H because of the competence of C2-H · · · O interactions with ethanol molecules, as well as the strong hydrogen-bond interactions between the BF4 − and the hydroxyls of the ethanol. Additionally, the most important is that both water and ethanol prefer to form hydrogen bonds with the proton H2 on imidazolium ring, rather than H4 and H5. These information would have important directive significance for studying the aggregation behavior and the structural organization of ILs in molecular solvents.

Synthesis and micellar properties of 1-decyl-2,3-dimethylimidazolium bromide surfactant in water and water-ethanolamine mixtures at 298.15 K

1-Decyl-2,3-dimethylimidazolium bromide (ddmimBr) has been synthesized by the reaction of 1,2-dimethylimidazole and 1-bromodecane. Micellization of ddmimBr surfactant in water (W) and water-ethanolamine (W-EA) with the weight percent of EA changing within the range 0-39.79%, has been investigated at 298.15 K. Information about the influence of the added EA on the critical micelle concentration (CMC) was obtained through density and surface tension measurements. This last provides information about the dependence of the surface excess concentration, the minimum area per surfactant molecule and the surface pressure at the CMC on the added weight percentage of organic solvent. The effect of binary aqueous mixtures of W-EA on the apparent molar volume (phi V) of the ddmimBr has been investigated. The apparent molar volume upon aggregation (Delta phi V) shows a maximum at about 15 wt% of EA, this behavior is discussed in terms of the changes of the solvent structure. Partial specific volume data, obtained by density measurements, indicate that the fraction of solvent molecules interact with the surfactant remained roughly constant.

Ionic liquid induced changes in the properties of aqueous zwitterionic surfactant solution

Modifying properties of aqueous surfactant solutions by addition of external additives is an important area of research. Unusual properties of ionic liquids (ILs) make them ideal candidates for this purpose. Changes in important physicochemical properties of aqueous zwitterionic N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) surfactant solution upon addition of hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4], are reported. Dynamic light scattering results indicate a dramatic reduction in the average micellar size in the presence of [bmim][BF 4]; micellar (or micelle-like) aggregation in the presence of as high as 30 wt % [bmim][BF 4] is confirmed. Responses from fluorescence probes are used to obtain critical micelle concentration (cmc), aggregation number ( N agg), and dipolarity and microfluidity of the micellar pseudophase of aqueous SB-12 in the presence of [bmim][BF 4]. In general, increasing the amount of [bmim][BF 4] to 30 wt % results in decrease in N agg and increase in cmc. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the micellar pseudophase is observed on increasing [bmim][BF 4] concentration in the solution. It is attributed to increased water penetration into the micellar pseudophase as [bmim][BF 4] is added to aqueous SB-12. It is proposed that IL [bmim][BF 4] behaves similar to an electrolyte and/or a cosurfactant when present at low concentrations and as a polar cosolvent when present at high concentrations. Electrostatic attraction between cation of IL and anion of zwitterion, and anion of IL and cation of zwitterion at low concentrations of [bmim][BF 4] is evoked to explain the observed changes. Presence of IL as cosolvent appears to reduce the efficiency of micellization process by reducing the hydrophobic effect.

Aggregation of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) in D2O: a NMR study

Aqueous solutions of five ionic liquids (ILs) of the 1-n-alkyl-3-methylimidazolium bromide family, [C(n)mim]Br (n = 4, 6, 8, 10, 12), were investigated by NMR measurements at 298.2 K as a function of IL concentrations. Critical aggregation concentrations and aggregation numbers of these ILs were determined by 1H NMR except for [C4mim]Br in D2O. The effects of the alkyl chain length of the cations were examined on the aggregation behavior of the ILs. 1H NMR data of the solvent D2O were used to investigate the hydration of the ILs in D2O, and it was found that the ionic hydration and the cation-anion association or aggregation of the ILs offset each other. The microenvironment of different protons of cations of the ILs in the aggregates was probed by determining the spin-lattice relaxation rate (1/T1). It is suggested that the imidazolium rings in the aggregates are exposed to water and that the molecular motion of the aggregates is more restricted than that of the monomers of the ILs. Furthermore, a stair-like microscopic aggregation structure is suggested for the [C(n)mim]Br/D2O (n = 6, 8, 10) systems from 2-D 1H-1H NOESY measurements.

Modulating properties of aqueous sodium dodecyl sulfate by adding hydrophobic ionic liquid

Altering and modifying important physicochemical properties of aqueous surfactant solutions is highly desirable as far as potential applications of such systems are concerned. Changes in the properties of aqueous solutions of a common anionic surfactant sodium dodecyl sulfate (SDS) are assessed in the presence of a common and popular 'hydrophobic' ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)). Upon addition of up to approximately 0.10 wt% bmimPF(6), a dramatic decrease in critical micelle concentration (cmc) is accompanied by an increase in the degree of counterion dissociation (alpha) and micellar aggregation number (N(agg)) indicating micellar growth. However, in the range 0.10 wt% < or = bmimPF(6) 2.00 wt%, relatively gradual decrease in alpha and N(agg) is observed along with no change in cmc. Significantly decreased microfluidity of the aqueous SDS solutions on addition of bmimPF(6) is indicated by a fluorescence microviscosity probe 1,3-bis-(1-pyrenyl)propane which suggests partitioning of bmimPF(6) into the SDS micellar phase. Behavior of solvatochromic fluorescence probes, pyrene, pyrene-1-carboxaldehyde, and 2-(p-toluidino)naphthalene-6-sulfonate, confirms interaction, and possible complexation, between IL bmimPF(6) and anionic micellar surface. Increased solubility of bmimPF(6) with increasing SDS concentration further confirms SDS-bmimPF(6) interactions. Presence of strong electrostatic attraction between bmim(+) and anionic micellar surface is proposed to be the most dominant reason for these observations. All-in-all, unique role of a hydrophobic ionic liquid bmimPF(6) in modifying the properties of aqueous anionic sodium dodecyl sulfate is demonstrated.