Block copolymer micelle shuttles with tunable transfer temperatures between ionic liquids and aqueous solutions

Four poly((1,2-butadiene)- block-ethylene oxide) (PB-PEO) diblock copolymers were shown to self-assemble into micelles with PB cores and PEO coronas (including spheres, cylinders, and vesicles) in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). All four systems exhibited the "micelle shuttle" (He, Y.; Lodge, T. P. J. Am. Chem. Soc. 2006, 128, 12666-12667), whereby PB-PEO micelles transferred, reversibly and with preservation of micelle structure, from an aqueous phase at room temperature to a hydrophobic ionic liquid at high temperature. The micelle size (both mean and distribution) depends on whether it was initially dissolved in water or in the ionic liquid, but the initial micelle structures in the ionic liquid were shown by dynamic light scattering to be preserved during the transfer and persist essentially unchanged for months in both the ionic liquid and water. The transfer was shown to be driven by the deteriorating solvent quality of water for PEO at high temperature, while the ionic liquid remains a good solvent. The transfer temperature could be tuned by adding ionic or nonionic additives to the aqueous phase to change the solvent quality of water for PEO, and by using ionic liquids with different polarity.     

Spontaneous phase transfer of thermosensitive hairy particles between water and an ionic liquid

This article describes the temperature-induced phase transfer behavior of a series of thermosensitive polymer brush-grafted particles between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). Six samples were made by surface-initiated atom transfer radical polymerization: silica particles grafted with poly(methoxypoly(ethylene glycol) methacrylate) (PPEGMMA) with two different molecular weights, poly(methoxytri(ethylene glycol) methacrylate) (PTEGMMA), poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA), and two copolymers of PEGMMA and TEGMMA with different compositions (P(PEGMMA-co-TEGMMA)-82 and P(PEGMMA-co-TEGMMA)-74). The cloud points of free PPEGMMA with M(n,SEC) of 23 and 40 kDa, P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA in [EMIM][TFSI]-saturated water were 95, 94, 80, 72, and 43 °C, respectively. PDEGMMA was not soluble in the ionic liquid-saturated water. PPEGMMA brush-grafted particles moved spontaneously and completely from water to the [EMIM][TFSI] phase upon heating at 80 °C. When cooled to 22 °C, all particles returned to the water layer. From UV-vis absorbance measurements, the transfer temperature (T(tr)) of PPEGMMA-grafted particles from water to the ionic liquid was 42 °C. Thermodynamic analysis showed that the particle transfer was an entropically driven process. P(PEGMMA-co-TEGMMA)-82, P(PEGMMA-co-TEGMMA)-74, and PTEGMMA brush-grafted particles also underwent reversible and quantitative transfer between the two phases upon heating at 70 °C and cooling at 0 °C; their transfer temperatures from water to [EMIM][TFSI] were 36, 30, and 16 °C, respectively. T(tr) was a linear function of the cloud point of the corresponding free polymer in ionic liquid-saturated water. In contrast, PDEGMMA-grafted particles moved spontaneously to the ionic liquid layer upon heating but did not return to water even after prolonged stirring at 0 °C.     

Self-assembly of block copolymer micelles in an ionic liquid

Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block constant. The nanostructures of the PB-PEO micelles formed in an ionic liquid were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extracted from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aqueous solutions of the same copolymers, [BMIM][PF(6)] solutions exhibit some distinct features, such as temperature-independent micellar morphologies between 25 and 100 degrees C. As in aqueous solutions, significant nonergodicity effects were also observed. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liquid, with potential applications in many arenas.     

Modification of carbon electrode in ionic liquid through the reduction of phenyl diazonium salt. Electrochemical evidence in ionic liquid

Electrochemical reduction of the 4-nitrophenyl diazonium salt in ionic liquid media has been investigated at carbon electrode. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The cyclic voltammetry study demonstrated the possibility of the electrochemical grafting of the nitrophenyl groups onto carbon electrode after the reduction of its corresponding diazonium in ionic liquid. The electrochemical characterization of the modified electrode achieved on ionic liquid displays the presence of the nitrophenyl group at the carbon surface. Moreover, the surface concentration of the attached group obtained in this media was found to be around 1.7 × 10⁻¹⁰ mol cm⁻², this value may suggest the possibility of the formation of monolayer. Furthermore, the characterization of the modified electrode in [EMIM][TFSI] showed the conversion of some NO₂-phenyl groups to NHOH-phenyl. This observation could indicate the presence of surface interaction between the reduced NO₂-phenyl and the ionic liquid cation, thanks to the presence of acidic proton in the ionic liquid cation.     

Liquid–Liquid Equilibrium Data for 1-Ethyl-3-methylimidazolium Acetate–Thiophene–Diesel Compound: Experiments and Correlations

Extraction of thiophene from cyclohexane, isooctane and toluene were performed using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) at T=298.15 K. The liquid?Cliquid equilibrium (LLE) experiments were performed on three systems, namely: [EMIM][OAc]?Cthiophene?Ccyclohexane, [EMIM][OAc]?Cthiophene?Cisooctane and [EMIM][OAc]?Cthiophene?Ctoluene. The LLE data showed that [EMIM][OAc] has a higher selectivity at low concentration of thiophene and also showed that the hydrocarbon-rich phase is free of ionic liquid. This implies that there will be no cross contamination and the ionic liquid will be a non-pollutant in fuel after extraction. Further, the amount of hydrocarbon in the ionic-liquid-rich phase is very small. This implies that ionic liquid can be regenerated with negligible loss of fuel. LLE data was then correlated using the NRTL and UNIQUAC models. These showed root mean square deviation (RMSD) values of 0.82?% and 1.46?% for the isooctane system, 1.37?% and 1.57?% for the cyclohexane system and 1.39?% and 1.53?% for the toluene system.     

Effect of water on the interfacial structures of room-temperature ionic liquids

The interfacial structures of cyano-based room-temperature ionic liquids play a very important role in reducing friction. However, the presence of water impairs their tribological performance. The interfacial structures and friction forces of 1-ethyl-3-methylimidazolium dicyanamide, [EMIM][DCN], and the effect of water on these structures and forces were investigated using atomic force microscopy. In addition, the interaction of water and [EMIM][DCN] was evaluated using Fourier-transform infrared (FT-IR) spectroscopy. Multiple repulsive layers were observed in the [EMIM][DCN] solution. This solution showed low friction force because these repulsive layers worked as protective layers against friction. On the other hand, the specific repulsive layer characteristics of [EMIM][DCN] could not be observed in a [EMIM][DCN] + 2 wt% H₂O solution. FT-IR results indicated that the layer structure of [EMIM][DCN] was disturbed by the addition of H₂O. Therefore, the solution containing water exhibited a high friction force.     

Intramolecular electron transfer within a covalent, fixed-distance donor-acceptor molecule in an ionic liquid

Intramolecular photoinduced charge separation and recombination within the donor-acceptor molecule 4-(N-pyrrolidino)naphthalene-1,8-imide-pyromellitimide, 5ANI-PI, are studied using ultrafast transient absorption spectroscopy in the room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [EMIM][Tf2N]. The rate constants of both photoinduced charge separation and charge recombination for 5ANI-PI in [EMIM][Tf2N] are comparable to those observed in pyridine, which has a static dielectric constant similar to that of [EMIM][Tf2N] but a viscosity that is nearly 2 orders of magnitude lower than that of [EMIM][Tf2N]. The electron-transfer dynamics of 5ANI-PI in [EMIM][Tf2N] are compared to those in pyridine as a function of temperature and are discussed in the context of recently reported ionic liquid solvation studies.     

Effect of anions on static orientational correlations, hydrogen bonds, and dynamics in ionic liquids: a simulational study

Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and PAdua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM+ is studied in the presence of three different anions, namely, chloride Cl-, tetrafluoroborate BF(4)(-), and bis((trifluoromethyl)sulfonyly)imide TF2N-. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF4] to [EMIM][TF2N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF2N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM][BF4] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.     

Vapor pressure measurement for water,methanol, ethanol,and their binary mixtures in the presence of an ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate

Vapor pressure data were measured for water, methanol and ethanol as well as their binary mixtures with an ionic liquid (IL) 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]) at varying temperature and IL-content ranging from mass fraction of 0.10–0.70 by a quasi-static method. The vapor pressure data for the IL-containing binary systems were correlated using NRTL equation with average absolute relative deviation (ARD) within 0.0076, and the binary NRTL parameters was used for predicting the vapor pressure of the IL-containing ternary systems with reasonable accuracy. In addition, the infinite activity coefficients of solvents in [EMIM][DMP] and isobaric vapor–liquid equilibrium for IL-containing ternary systems at 101.325 kPa and mass fraction of IL being 0.5 were predicted with the regressed NRTL parameters. The results indicate that ionic liquid [EMIM][DMP] can depress the volatility of the solvents of water, methanol and ethanol but to a varying degree, leading to the variation of relative volatility of a solvent and even removal of azeotrope for water–ethanol mixture.     

Cyclic voltammetry of Th(IV) in the room-temperature ionic liquid [Me3NnBu][N(SO2CF3)2

A Th(IV) compound, [Th(TFSI)4(HTFSI)].2H2O [where TFSI = N(SO2CF3)2], has been synthesized and characterized using elemental analysis, thermogravimetric analysis, and vibrational spectroscopy. The analysis suggests that the TFSI anion coordinates to the metal center via the sulfonyl oxygens as well as provides evidence for the coordination of HTFSI. The voltammetric behavior of this compound has been studied in the room-temperature ionic liquid [Me3NnBu][TFSI], and results show that Th(IV) is reduced to Th(0) in this ionic liquid in a single reduction step. Analysis of cyclic voltammograms shows that an insoluble product is being formed at the electrode surface, which is attributed to the formation of ThO2 by reaction with water. The E0 value for the reduction of Th(IV) to Th(0) has been determined to be -2.20 V (vs Fc+/Fc; -1.80 V vs SHE). A comparison of this E0 value with those obtained for Th(IV) reduction in a LiCl-KCl eutectic (400 degrees C), water, and nonaqueous solvents shows that the reduction in [Me3NnBu][TFSI] is easier to accomplish than that in these other solvents.     

Temperature- and pH-triggered reversible transfer of doubly responsive hairy particles between water and a hydrophobic ionic liquid

This article reports on the synthesis of thermo- and pH-sensitive polymer-brush-grafted silica particles ("hairy" particles) and the study of their phase-transfer behavior between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIM][TFSA]), in response to temperature and pH changes. The hairy particles were made by the surface-initiated atom transfer radical polymerization of methoxytri(ethylene glycol) methacrylate (TEGMMA) and tert-butyl methacrylate with a molar ratio of 100:11 in the presence of a free initiator and the subsequent removal of tert-butyl groups. The cloud points (CPs) of poly(TEGMMA-co-methacrylic acid), obtained after the treatment of the free polymer with trifluoroacetic acid, in both water and [EMIM][TFSA]-saturated water increased with the increase in pH and can be tuned over a wide temperature range. The hairy particles moved spontaneously from the aqueous phase to the [EMIM][TFSA] phase upon heating at 80 °C and returned to the aqueous layer upon cooling at 10 °C. This process can be repeated many times regardless of whether the pH of the aqueous phase is 2.99, 5.00, or 7.02. UV-vis absorbance measurements showed that the transfer temperature (T(tr)) of hairy particles from water to [EMIM][TFSA] increased with the increase in the pH of the aqueous phase. A linear relationship was observed between the T(tr) of hairy particles and the CP of the corresponding free polymer. By taking advantage of the tunability of the T(tr) of hairy particles, we demonstrated the pH-driven reversible transfer of hairy particles at a fixed temperature by changing the pH of the aqueous phase and multiple phase-transfer processes by controlling both the temperature and pH.     

离子液体[EMIM][PF6]负载纳米SiOx表面的熔点及结构

制备了离子液体(1-乙基-3-甲基咪唑六氟磷酸 [EMIM][PF₆])负载量不同的多孔纳米氧化硅(SiO_x), 并采用差式扫描量热分析(DSC)、X射线衍射(XRD)、激光Raman光谱、傅里叶变换红外(FTIR)光谱分析等手段研究离子液体负载纳米氧化硅后的熔点变化及相行为. 研究表明负载于纳米氧化硅表面的离子液体熔点明显下降, 且负载于不同表面羟基含量的氧化硅表面熔点下降幅度不同. 纯离子液体[EMIM][PF₆]熔点为62 ℃, 在纳米氧化硅表面负载量为35%时熔点为52 ℃, 比负载前下降10 ℃; 负载于另两种不同羟基含量的纳米氧化硅表面后熔点分别下降20和17 ℃. 而同一种纳米氧化硅(比表面积为640 m²·g^-1)在负载量小于50%时, 熔点下降明显; 进一步增大负载量, 熔点逐渐趋于本体. XRD和Raman光谱分析显示, 离子液体负载于氧化硅表面后其衍射峰或吸收峰相对强度发生明显改变. 分析负载前后纳米氧化硅的结构变化, 推断离子液体熔点下降的主要原因是离子液体分子与纳米氧化硅表面之间存在强烈的界面相互作用, 而表面羟基的密度及比表面积是影响负载后[EMIM][PF₆]离子液体相行为的主要因素.     

The micellar shuttle: thermoreversible, intact transfer of block copolymer micelles between an ionic liquid and water

Poly(1,2-butadiene-block-ethylene oxide) (PB-PEO) block copolymer micelles are found to partition reversibly between an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and water, thereby functioning as micellar shuttles controlled simply by temperature. The micelle size and structure are preserved during this reversible phase transfer. This phenomenon offers a simple means to transport chemicals back and forth between two immiscible phases.     

A novel method to prepare polymer-ionic liquid gel under high pressure and its electrochemical properties

Sol–gel transition behavior of ionic liquid gel based on poly (ethylene glycol) (PEG) and ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO₄] has been investigated under the pressure up to 250 MPa. The Temperature versus Pressure phase diagram of PEG/[EMIM][EtSO₄] gel is constructed, and it indicates that the melting point is an increasing function of pressure. Based on the phase diagram, the PEG/[EMIM][EtSO₄] gels are prepared by cooling under the pressure of 300 MPa and atmospheric pressure, respectively. From the differential scanning calorimetry result of the recovered samples, it is found that PEG/[EMIM][EtSO₄] gel prepared under high pressure has a higher crystallinity and smaller crystal size polymer network, comparing with under atmospheric pressure. The cyclic voltammograms and impedance spectra tests indicate that the PEG/[EMIM][EtSO₄] gel prepared under high pressure exhibit higher ionic conductivity comparing with atmospheric pressure. It could be speculated these excellent properties might be attributed to the loose gel structure and high ionic density induced by high pressure.     

Temperature-responsive phase transition of polymer vesicles: real-time morphology observation and molecular mechanism

Novel thermosensitive polymer vesicles with controlled temperature-responsive phase transition at the lower critical solution temperature (LCST) varying from 8 to 81 degrees C were prepared via self-assembly of amphiphilic hyperbranched star copolymers having a hydrophobic hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HBPO) core and many hydrophilic polyethylene oxide (PEO) arms. Real-time optical microscopic observation revealed that the polymer vesicles have undergone sequential morphology changes including enrichment, aggregation, fusion, and vesicle-to-membrane transformation near the LCST. Molecular-level investigation indicates that the LCST transition results from the decreasing water solubility of the polymer vesicles with increasing temperature based on the partial dehydration of the PEO vesicle corona. On the basis of these results, a LCST transition mechanism, in view of the molecular configuration, balance of hydrophilic and hydrophobic moieties, and the vesicle morphology transformations, was proposed. As far as we know, the work presented here is the first demonstration of thermosensitive vesicles based on PEO, and the finding may be useful to design the thermosensitive core-shell structures by introducing the PEO segments.     

Preparation of Composite Polymer Particles by Seeded Dispersion Polymerization in Ionic Liquids

Summary: Submicron-sized monodisperse PS particles were prepared by dispersion polymerization of styrene in ionic liquids with poly(vinylpyrrolidone) as stabilizer. Seeded dispersion polymerization of MMA was subsequently carried out with PS seeds in [Bmim][BF₄] to prepare PS/PMMA composite particles. Observation of the obtained particles of ultrathin cross-sections with a scanning and transmission electron microscope revealed that no secondary nucleation occurred during the seeded dispersion polymerization and that the particles have a core-shell morphology consisting of a PS core and a PMMA shell. Successful preparation of PS/PMMA composite particles in an ionic liquid has thus been demonstrated. Moreover, PS/PAA (PS-core/PAA-shell) composite particles were prepared by seeded dispersion polymerization in [DEME][TFSI], illustrating that hydrophobic/hydrophilic composite particles can be readily prepared in the ionic liquid.     

Revealing the influence of the strength of coulomb interactions on the viscosity and interfacial tension of ionic liquid cosolvent mixtures

Within this work, viscosity and interfacial tension of selected ionic liquid cosolvent mixtures, [EMIM][EtOSO3] (1-ethyl-3-methyl-immidazolium ethyl sulfate) with water and ethanol, were studied as a function of composition by surface light scattering (SLS) and the pendant drop method in a consistent manner, allowing a close insight into the nature of interactions. Here, we show that the viscosity behavior clearly reflects the bulk structure of the ionic liquid cosolvent mixtures and correlates to the fluid structure at the phase boundary. In contrast to former work, we found the viscosity of ionic liquid [EMIM][EtOSO3] to be decreasing the stronger by small amounts of the cosolvents and the lower their dielectric constant. Furthermore, two distinct trends for the dependence of the viscosity on the cosolvent concentration were resolved. These were assigned to ion-dipole interactions dominating in the salt-rich region and to dipole-dipole interactions in the diluted one. A crossover between both regions is reflected by the interfacial tension data, where it seems that up to a "critical" concentration almost no cosolvent is present at the phase boundary.     

Structural characterization of a lanthanum bistriflimide complex, La(N(SO2CF3)2)3(H2O)3, and an investigation of La, Sm, and Eu electrochemistry in a room-temperature ionic liquid, [Me3N(n)Bu][N(SO2CF3)2

The reduction of selected lanthanide cations to the zerovalent state in the room-temperature ionic liquid [Me3N(n)Bu][TFSI] is reported (where TFSI = bistriflimide, [N(SO2CF3)2]-). The lanthanide cations were introduced to the melt as the TFSI hydrate complexes [Ln(TFSI)3(H2O)3] (where Ln = La(III), Sm(III) or Eu(III)). The lanthanum compound [La(TFSI)3(H2O)3] has been crystallographically characterized, revealing the first structurally characterized f-element TFSI complex. The lanthanide in all three complexes was shown to be reducible to the metallic state in [Me3N(n)Bu][TFSI]. For both the Eu and Sm complexes, reduction to the metallic state was achieved via divalent species, and there was an additional observation of the electrodeposition of Eu metal.     

The performance of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid as mobile phase additive in HPLC‐based lipophilicity assessment

Ionic liquids have been widely used as green alternative mobile phase additives to shield the residuals silanols groups and modify the stationary/mobile phase HPLC systems. The present study aimed to evaluate the performance of the ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM][BF4]) in producing extrapolated logk_w indices suitable to substitute for octanol–water logP or logD values. The effect of [EMIM][BF4] was investigated for a set of basic and neutral drugs using two different columns, BDS and ABZ⁺. [EMIM][BF4] was added simply alone or in combination with n‐octanol and was compared with the conventional masking agent n‐decylamine. [EMIM][BF4] reduced the retention by suppressing silanophilic interactions, althoug to a lower extent than n‐decylamine. Addition of n‐octanol further decreased the retention by shielding silanol sites on BDS and/or interacting with polar groups through hydrogen bonding on ABZ⁺. Logk_w/logD_7.4 relationships proved moderate compared with those derived upon addition of n‐decylamine. They were considerably improved upon the introduction of protonated fraction F⁺ in the correlation, reflecting ion pair formation between the chaotropic anion [BF4]^‐ and the protonated basic compounds. In this aspect, the ionic liquid [EMIM][BF4], although efficient as a masking agent, cannot be recommended as mobile phase additive to reproduce octanol–water partitioning. Copyright © 2010 John Wiley & Sons, Ltd.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized in hyaluronic acid and room temperature ionic liquids composite film

A novel biocomposite film based on hyaluronic acid (HA) and hydrophilic room temperature ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM][BF₄]) was explored. Here, HA was used as a binder to form [EMIM][BF₄]-HA composite film and help [EMIM][BF₄] to attaching on glass carbon electrode (GCE) surface, while doping [EMIM][BF₄] in HA can effectively reduce the electron transfer resistance of HA. The composite film can be readily used as an immobilization matrix to entrap myoglobin (Mb). A pair of well-defined and quasi-reversible redox peaks of Mb was obtained at the Mb-[EMIM][BF₄]-HA composite film modified GCE (Mb-[EMIM][BF₄]-HA/GCE) through direct electron transfer between Mb and the underlying electrode. The Mb-[EMIM][BF₄]-HA/GCE showed an excellent electrocatalytic activity toward the reduction of H₂O₂. Based on the [EMIM][BF₄]-HA biocomposite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.