Neat Liquid Research Articles

Effect of methylimidazole on cellulose/ionic liquid solutions and regenerated material therefrom

Cellulose, especially wood-based cellulose, is increasingly important for making everyday materials such as man-made-regenerated textile fibers, produced via dissolution and subsequent precipitation. In this paper, the effect of cosolvents in ionic liquid-facilitated cellulose dissolution is discussed. Both microcrystalline cellulose and dissolving grade hardwood pulp were studied. Three different cosolvents in combination with ionic liquid were evaluated using turbidity measurements and viscosity. The ionic liquid precursor N-methylimidazole proved to be a promising cosolvent candidate and was thus selected for further studies together with the ionic liquid 1-ethyl-3-methylimidazolium acetate. Results show that dissolution rate can be increased by cosolvent addition, and the viscosity can be significantly reduced. The solutions were stable over time at room temperature and could be converted to regenerated textile fibers with good mechanical properties via airgap spinning and traditional wet spinning. Fibers spun from binary solvents exhibited significantly higher crystallinity than the fibers from neat ionic liquid.

Efficient Palladium Catalysts Containing Original Imidazolium-Tagged Chiral Diamidophosphite Ligands for Asymmetric Allylic Substitutions in Neat Ionic Liquid

New imidazolium-tagged chiral diamidophosphite ligands, (S,S)-a and (R)-b, derived from (S,S)-N,N′-dibenzyl-1,2-cyclohexanediamine and (R)-N,N′-dimethyl-1,1′-binaphthyl-2,2′-diamine, respectively, and the corresponding palladium allylic complexes of general formula [PdCl(η3-2-Me-C3H4)(κ1P-L)]BF4 (1a,b) and [Pd(η3-2-Me-C3H4)(κ1P-L)2](BF4)3 (2a,b) were synthesized and fully characterized, including the X-ray crystal structure for 1b. These original Pd/L catalytic systems were applied in asymmetric allylic alkylation, amination, and sulfonylation using rac-3-acetoxy-1,3-diphenyl-1-propene as a substrate in neat ionic liquids, [bmim][PF6] and [Pyr][NTf2]. The best results in terms of enantioselectivity were obtained with the catalytic precursor 1b in [Pyr][NTf2]. The catalytic phase containing 1b for the allylic amination could be recycled up to six times without significant loss of asymmetric induction.

(−)‐R‐Mevalonolactone Studied by ROA and SERS Spectroscopy

Here we present for the first time the experimental and theoretical (DFT/B3LYP/6-311++G**) Raman optical activity (ROA) spectra of (-)-R-mevalonic acid as the δ-lactone form in neat liquid and in the aqueous solution. Quantum chemical calculations show the conformational diversity of (-)-R-mevalonolactone originated from small energy differences between the various conformation of the six-membered ring and the arrangement of the hydroxyl group. According to calculations, the investigated compound takes predominantly the chair conformation with the hydroxyl group in axial position, but the contribution of the other chair and boat conformers in the equilibrium at room temperature is not negligible. Additionally, we present normal Raman and the surface enhanced Raman (SERS) spectra of (-)-R-mevalonolactone adsorbed on the colloidal silver.

Non-Flammable Electrolyte Mixtures of Ringed Ammonium-Based Ionic Liquids and Ethylene Carbonate for High Voltage Li-Ion Batteries

Three ionic liquids based on ringed ammonium cations with different ring sizes [seven: azepanium; six: piperidinium; five: pyrrolidinium] and imide anion mixed with ethylene carbonate, EC, have been evaluated as electrolytes in high voltage lithium-ion batteries. It is found that mixing the ionic liquids with ethylene carbonate gives electrolyte mixtures with lower viscosities, increased conductivities and improved electrochemical cathodic stability than the neat ionic liquids. The flammability and thermal stability of the electrolytes have been studied by open-cup flash point measurements and thermogravimetric analysis combined with Infrared and Mass Spectroscopy. It is found that the neat ionic liquids have good thermal stability above 300°C and no flammability compared to carbonate-based electrolyte but upon mixing with EC the mixture decomposes at temperature below 130°C but stays non-flammable. The electrolyte mixtures have been evaluated in Li/LiMn1.5Ni0.5O4 (LMNO) and graphite/Li half cells and in the presence of fluoroethylene carbonate additive. Discharge capacities reaching 112–117 mAh.g−1 and 280–293 mAh.g−1 with coulombic efficiencies of 95% and 99% were obtained for graphite and LMNO, respectively, over 100 cycles at C/12.

Integration of UV-cured Ionogel Electrolyte with Carbon Paper Electrodes

A test bed with a coplanar architecture is employed to investigate the integration of an <em>in situ</em> cross-linked, polymer-supported ionogel with several commercially available, high surface area carbon paper electrodes. Specifically, a UV-cured poly(ethylene glycol) diacrylate (PEGDA)-supported ionogel electrolyte film is formed <em>in situ</em> against a variety of porous electrodes comprising: a carbon fiber paper, a carbon aerogel paper, and four carbon nanotube-based papers. Electrochemical impedance spectroscopy measurements reveal that the relative performance of a particular carbon paper with the neat ionic liquid is not necessarily indicative of its behavior when integrated with the solid ionogel electrolyte. The coplanar test bed can therefore serve as a useful tool to help guide the selection of suitable carbon-based electrode structures for supercapacitors that incorporate UV-cured ionogels created <em>in situ</em> for wearable energy storage applications.

Ionic liquid clusters: structure, formation mechanism, and effect on the behavior of ionic liquids

The microstructure of ionic liquids (ILs) has attracted much attention due to their relevance in physiochemical properties and behavior of ILs. The existence of clusters (or microheterogeneous structure) is one of the main features for many ILs, which provides fundamental information for understanding the performance of ILs in their applications. This perspective concentrates on the recent progresses in IL clusters research. Firstly, we give a brief introduction on the structure of clusters in neat ILs and IL solutions. Secondly, the possible formation mechanism of the IL clusters is described. Then, the effects of the clusters on the physicochemical properties, interfacial properties, confined geometry and assembly processes of ILs are discussed. Finally, we address the associated challenges and prospects on the future study of IL clusters.

Synthesis and Characterization of Guanidinium-Based Ionic Liquids as Possible Electrolytes in Lithium-Ion Batteries

Two guanidinium-based ionic liquids (ILs), N-cyclohexyl-N,N′,N′,N″,N″-pentamethylguanidinium bis(trifluoromethylsulfonyl) imide (Me5cHexGua-TFSI) and N,N-bis(2-ethylhexyl)-N′,N′,N″,N″-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide (Me4(2-EtHex)2Gua-TFSI), were synthesized and investigated for their applicability as electrolyte components for lithium-ion batteries. Various properties, such as conductivity, viscosity, potential window at a platinum electrode and eventually the compatibility with graphite, Li4Ti5O12 (LTO) and LiFePO4 (LFP) electrodes were determined for the neat ILs and for electrolytes from these ILs with 0.3 mol/kg LiTFSI as conductive salt. The viscosities of the neat guanidinium-based ILs are 385 mPas and 683 mPas at 23°C for Me5cHexGua-TFSI and Me4(2-EtHex)2Gua-TFSI, respectively, and the conductivities are 0.67 and 0.18 mS/cm at 25°C. In the presence of 0.3 mol/kg LiTFSI the conductivities decreased to 0.29 and 0.10 mS/cm, respectively. Both ILs reached anodic stabilities of 4.8 V vs. Li/Li+ and showed cathodic stabilities of 0.6 V vs. Li/Li+. The guanidinium-based electrolytes can be applied with LTO and LFP electrodes, but are not compatible with graphite electrodes. The results obtained for guanidinium-based ILs/electrolytes are compared with those of a carbonate-based electrolyte [1 M LiPF6 in EC:DMC (1:1, w/w)], and a pyrrolidinium-based IL/electrolyte [1-butyl-1-methylpyrrolidinium-TFSI (BMPL-TFSI) and 0.3 mol/kg LiTFSI in BMPL-TFSI].

Novel polysilsesquioxane hybrid polymer electrolytes for lithium ion batteries

A novel inorganic–organic hybrid crosslinker was prepared through synthesis of a fully condensed, high molecular weight ladder-like poly(methacryloxypropyl)silsesquioxane (LPMASQ) in one pot with a facile, base-catalysed system. The fully condensed LPMASQ revealed good thermal (∼380 °C) and electrochemical stability (∼5.0 V) due to the absence of uncondensed silanol groups. LPMASQ also revealed good solubility in various organic solvents and fully gelated 1 M LiPF6 in ethyl carbonate–diethyl carbonate (EC–DEC, 3/7, v/v) electrolyte solution through fast thermal and photocuring even at a very low concentration of 2 wt%. These observations were attributed to the polymeric nature of LPMASQ containing over one hundred methacryl moieties on the rigid double-stranded siloxane backbone. To the best of our knowledge, formation of a gel polymer electrolyte with 2 wt% gelator is the smallest gelation concentration that has ever been reported. This leads to high ionic conductivity (∼6.0 mS cm−1), excellent Coulombic efficiency and battery cell performance, comparable with those of the neat liquid electrolyte. The small crosslinker content, thermal and electrochemical stability, fast thermal and photocuring and facile processing of the LPMASQ based GPEs, as well as excellent Li battery cell performances strongly hold great promise for future industrial battery applications.

Aqueous Ionic Liquids and Deep Eutectic Solvents for Cellulosic Biomass Pretreatment and Saccharification.

Ionic liquids (ILs) have proven effective solvents for pretreating lignocellulose, leading to the fast saccharification of cellulose and hemicellulose. However, the high current cost of most ILs remains a major barrier to commercializing this recent approach at a practical scale. As a strategic detour, aqueous solutions of ILs are also being explored as less costly alternatives to neat ILs for cellulose pretreatment. However, limited studies on a few select IL systems are known and there remains no systematic survey of various ILs, eluding an in-depth understanding of pretreatment mechanisms afforded by aqueous IL systems. As a step toward filling this gap, this study presents results for Avicel cellulose pretreatment by neat and aqueous solutions (1.0 and 2.0 M) of 20 different ILs and three deep eutectic solvents, correlating enzymatic hydrolysis rates of pretreated cellulose with various IL properties such as hydrogen-bond basicity, polarity, Hofmeister ranking, and hydrophobicity. The pretreatment efficiencies of neat ILs may be loosely correlated to the hydrogen-bond basicity of the constituent anion and IL polarity; however, the pretreatment efficacies for aqueous ILs are more complicated and cannot be simply related to any single IL property. Several aqueous IL systems have been identified as effective alternatives to neat ILs in lignocellulose pretreatment. In particular, this study reveals that aqueous solutions of 1-butyl-3-methylimidazolium methanesulfonate ([BMIM][MeSO3]) are effective for pretreating switchgrass (Panicum virgatum), resulting in fast saccharification of both cellulose and hemicellulose. An integrated analysis afforded by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and cellulase adsorption isotherm of lignocellulose samples is further used to deliver a more complete view of the structural changes attending aqueous IL pretreatment.

Physicochemical investigation of chemical paint removers: Interactions of methylene chloride with polyurethane coatings

A variety of thermal and spectroscopic techniques have been used to investigate interactions of the widely-used paint-stripping solvent methylene chloride upon model polyurethane coatings. Thermal analysis reveals that methylene chloride penetrates and swells the polymer film and leads to a slight depression in the glass transition temperature (Tg) after drying. The 1H NMR spectra and T1 and T1ρ relaxation times show that methylene chloride is responsible for increased polymer segmental motion in the polymer due to swelling, and indicate intimate contact between the methylene chloride molecules and the polymer, with no liquid-like pools of the solvent observed. The quadrupolar-echo 2H NMR spectra of CD2Cl2 in the polyurethane over a temperature range of 24°C to −27°C reveal a lengthening of the rotational correlation times of the methylene chloride by over four orders of magnitude compared to the neat liquid, indicating restricted mobility due to an interaction with the polymer. Although this interaction is likely due to the electric dipoles in the solvent and the polymer backbone, the absence of significant residual nuclear quadrupole couplings due to a high degree of ordering or solvent immobilization shows that the interaction strength is weak compared to thermal energy (kT). Raman spectroscopy indicates that methylene chloride causes swelling by interacting with the carbonyl group responsible for inter-chain bonding, thus permitting dilation. FTIR and Raman spectroscopy demonstrated that methylene chloride leads to no irreversible chemical changes in the coating. A common cellulosic chemical stabilizer used in commercial paint removers has been found by XPS to deposit as a thin conformal but heterogeneous coating on the surface of the polymer, suggesting a possible important function to retard evaporation while allowing some permeation. PurposeCommercial military paint stripper is effective because it contains methylene chloride; in order to replace it, understanding its mechanism of action/interaction with the coating is crucial.

Analysis of household ignitable liquids and their post-combustion weathered residues using compound-specific gas chromatography-combustion-isotope ratio mass spectrometry

The continuing rise in home and vehicular arson cases involving the use of ignitable liquids continues to be an area of concern for criminal and civil investigators. In this study, the compound-specific δ13C values of various components of four flammable household chemicals were measured using a single quadrupole mass spectrometer and an isotope ratio mass spectrometer as simultaneous detectors for a gas chromatograph. Whereas compound-specific carbon isotope ratios were able to discriminate between different sources of neat (pre-combustion) ignitable liquids, analyses of the post-combustion residues were problematic. Weathering caused by combustion resulted in a significant increase in the 13C content of specific peaks relative to the neat liquids (i.e. less negative delta values) such that the isotopic comparison of pre- and post-combustion residues resulted in fractionation ranging from 0 to +10‰. Because of the current lack of understanding of isotopic fractionation during combustion, and because of problems encountered with co-elution in the more complex samples, compound-specific IRMS does not appear to be suitable for fire debris analysis. The comparison of non-combusted or non-weathered ignitable liquids is much more reliable, especially for relatively simple mixtures, and is best suited for exclusionary purposes until such time as a comprehensive database of samples is developed. Without a measure of the population variance, one cannot presently predict the false positive identification rate for the comparison of two ignitable liquids; i.e. the probability that two random ignitable liquid samples have indistinguishable isotope ratios.

Friction and anti-wear properties of two tris(pentafluoroethyl)trifluorophosphate ionic liquids as neat lubricants

The tribological behaviour was evaluated for two ionic liquids (ILs) as neat lubricants for the sliding pair stainless steel AISI420 and 100Cr6 under four loads (14, 18, 22 and 26N). The ILs contain the same anion, tris(pentafluoroethyl)trifluorophosphate [(C2F5)3PF3]− (also known as [FAP]−), combined with the cations 1-butyl-2,3-dimethylimidazolium [C4C1C1Im]+ or trihexyl(tetradecyl)phosphonium [P6,6,6,14]+. The IL [P6,6,6,14][(C2F5)3PF3] showed always better lubricating properties than [C4C1C1Im][(C2F5)3PF3] in terms of friction coefficient and wear volume. Under the same conditions, tribological tests were performed with two perfluoropolyethers as reference lubricants developing, in general, higher friction coefficients and also higher wear volumes than those obtained with both ILs. Surface interactions were studied by SEM observations and XPS analyses of the neat ILs and of the wear tracks.

ChemInform Abstract: The Solid‐State Structure of SF4: The Final Piece of the Puzzle.

AbstractCrystals of SF4 are obtained by slow cooling of neat liquid SF4 and by crystallization from CF2Cl2 solvent.

Formal Redox Potentials of Organic Molecules in Ionic Liquids on the Basis of Quaternary Nitrogen Cations as Adiabatic Electron Affinities

Formal redox potentials E°' involving neutral species R and radical anions R(•-) in ionic liquids (ILs) composed of ammonium, pyridinium, and imidazolium cations are discussed from the point of view of the adiabatic electron affinity as a molecular property. The dependence of the 1,4-benzoquinone (BQ)/BQ(•-) redox process in CH2Cl2 and CH3CN is primarily investigated over a wide concentration range of ILs as the supporting electrolyte. A logarithmic relationship involving a positive shift of E°' with increasing concentration is obtained when the concentration is changed from 0.01 to 1.0 M. The relationship of E°' at IL concentrations greater than 1.0 M gradually reaches a plateau and remains there even for the neat ILs. It is found that the E°' values in the neat ILs are not influenced by the measurement conditions, and that they remain considerably dependent on the nature and concentration of the electrolyte when measured using the traditional method involving molecular solvents combined with a supporting electrolyte (0.1-0.5 M). The difference in the E°' values observed in the ammonium and pyridinium ILs is only several millivolts. In addition, ESR and self-consistent isodensity polarized continuum model calculation results reveal that the potential shift toward positive values upon the transition from molecular solvents containing ILs to neat ILs is adequately accounted for by changes in the electrostatic interaction of R(•-) taken into the cavity composed of the solvent and IL. On the other hand, the first reduction waves of quinones, electron-accepting molecules, and polynuclear aromatic hydrocarbons are reversibly or quasi-reversibly observed in the ILs. The electrochemical stability of the ILs is exploited in the facile measurement of these quasi-reversible waves at quite negative potentials, such as for the naphthalene (NP)/NP(•-) couple. Notably, the E°' values obtained in the ammonium ILs correlate well with the calculated standard redox potentials and are linearly fitted with high correlation over all classes of compounds using a single regression equation based on Koopmans' theorem.

Theoretical study of the conformational equilibrium of 1,4-dioxane in gas phase, neat liquid, and dilute aqueous solutions

The conformational equilibrium of 1,4-dioxane in the gas phase, in the pure liquid, and in aqueous solution has been studied by means of the Average Solvent Electrostatic Potential from Molecular Dynamics (ASEP/MD) method and the Integral Equation Formalism for the Polarizable Continuum Model (IEF-PCM). The dioxane molecule was described at the DFT(B3LYP)/aug-cc-pVTZ level. In the three phases, the equilibrium is almost completely shifted toward the chair conformer, with populations of the twist-boat conformers lower than 0.01 %. The equilibrium is dominated by the internal energy of the molecule, as the solute–solvent interaction free energies are very similar in the three conformers considered (chair, 1,4 twist-boat, and 2,5 twist-boat). In the pure liquid, where the dioxane–dioxane interaction is dominated by the Lennard-Jones term, the structure is characteristic of a van der Waals liquid. However, the decrease in the C–H distance from gas phase to solution, the increase in the C–H vibrational frequencies, and the presence of a shoulder in the O–Haxial pair radial distribution function point to the presence of a weak C–H–O hydrogen bond. The analysis of the occupancy maps of water oxygen and hydrogen atoms around the 1,4-dioxane molecule confirms this conclusion. Contrary to what is found in small water-dioxane clusters, in the liquid, there is a preference for oxygen atoms to interact with axial hydrogen atoms to form C–H–O hydrogen bonds. Comparison of ASEP/MD and IEF-PCM results indicates that including specific interactions is very important for an adequate description of the solute–solvent interaction; however, the influence of these interactions does not translate in changes in the relative stability of the conformers because it cancels out when energy differences are calculated.

Time-resolved laser spectroscopy of nonreactive processes in ionic liquids and their binary mixtures with organic solvents and CO2

Nonreactive dynamics of molecules in ionic liquids (ILs) have been investigated in various environments, such as in neat aprotic and protic ILs, as well as in binary mixtures of ILs with polar organic solvents and CO2. Transient broadband absorption and fluorescence spectroscopic techniques on timescales from femtoseconds to milliseconds have been applied to elucidate the importance of different types of solute–solvent interactions in these media. Molecular probes such a 12′-apo-β-carotenoic-12′-acid and Coumarin C153 have been used as reporter molecules for ionic liquid solvation dynamics, micropolarity, hydrogen-bonding and collisional relaxation. With Coumarin C153 in ILs, the relationship between the complete solvation response and microwave-terahertz absorption measurements of the neat liquid was explored quantitatively. A reduced value for the conductivity plays a key role in such solvation experiments. Aprotic ILs exhibit a micropolarity larger than expected from their static dielectric constants, whereas the local polarity of protic alkylammonium formate ILs appears to be similar to that of alcohols having comparable dielectric constants. In IL mixtures with organic solvents or CO2, there is no indication for differences in the bulk composition and the local composition around the molecular probe. Collisional relaxation processes in ILs take place on similar timescales as in dipolar organic solvents.

Distribution of 1-Butyl-3-methylimidazolium Bistrifluoromethylsulfonimide in Mesoporous Silica As a Function of Pore Filling

Rotational dynamics of the ionic liquid (IL) 1-butyl-3-methylimidazolium bistrifluoromethylsulfonimide, [C4mim][Tf2N], 1, as a neat liquid, and confined in mesoporous silica were investigated by 1H spin–spin (T2) and spin–lattice (T1) relaxation measurements and 13C NMR spectroscopy. Translational dynamics (self-diffusion) were monitored via the diffusion coefficient, D, obtained with 1H pulsed field gradient NMR measurements. These data were used to determine the distribution of 1 in the pores of KIT-6, a mesoporous silica with a bicontinuous gyroid pore structure, as a function of filling fraction. Relaxation studies performed as a function of filling factor and temperature reveal a dynamic heterogeneity in both translational and rotational motions for 1 at filling factors, f = 0.2–1.0 (f = 1 corresponds to fully filled pores). Spin–lattice and spin–spin relaxation times reveal that the motion of 1 in silica mesopores conforms to that expected for a two-dimensional relaxation model. The relaxation dynam...

Influence of the Water Content on the Structure and Physicochemical Properties of an Ionic Liquid and Its Li+ Mixture

The effect of water on the hydrophobic ionic liquid (IL) 1-n-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonylimide) and its Li(+) mixture was evaluated. The electrochemical stability, density, viscosity, and ionic conductivity were measured for both systems in different concentrations of water. The presence of Li(+) causes a large increase in the water absorption ability of the IL. The experimental results suggest a break of the interactions between Li(+) and Tf2N(-) anions in the strong aggregates formed in dried Li(+) mixtures, modifying the size and physicochemical nature of these aggregates. It is also observed that the size of the ions aggregates with formal charge increases at high temperature and decreases the mobility of the charge carrier, explaining the break in the Walden rules at high temperature. Raman spectroscopy and molecular dynamic simulations show the structural change of these systems. In neat ILs, the water molecules interact mainly among each other, while in the Li(+) mixtures, water interacts preferentially with the metallic cation, causing an important change in the aggregates present in this system.

Charge-Transfer Electronic Absorption Spectra of 1-Ethylpyridinium Cation and Halogen Anion Pairs in Dichloromethane and as Neat Ionic Liquids

The charge-transfer (CT) absorption bands of ion pairs composed of 1-ethylpyridinium (Epy(+)) and halogen anions (X(-): Cl, Br, or I) were measured in dichloromethane solutions of EpyX. The CT band of the Epy(+)I(-) ion pair shows clear splitting because of spin-orbit interaction in the excited state. The CT transition energy of an Epy(+)X(-) ion pair in a dichloromethane solution is related to electron affinity of X, which is in accordance with the Mulliken theory for CT bands. Extinction coefficients for the CT bands of the Epy(+)X(-) ion pairs in dichloromethane were determined using the measured absorbance, and the ion-pair concentration was estimated on the basis of electroconductivity. Structures of Epy(+)X(-) ion pairs were also evaluated on the basis of both quantum-chemical calculations and NMR spectroscopy. In addition, in the absorption spectrum measured for neat EpyI liquid, a broad band appeared at a longer wavelength side of the S1(ππ*) band. This new band has been assigned to the CT band of the Epy(+)I(-) ion pair formed in neat EpyI liquid.

Highly permeable ionic liquid/Cu composite membrane for olefin/paraffin separation

1-Methyl-3-octyl imidazolium tetrafluoroborate (MOIM+BF4-) ionic liquid was introduced for olefin/paraffin separation since it exists primarily as its free ions. It is expected that most of the free imidazolium cations will interact with olefin molecules and the free anions will positively polarize the Cu nanoparticles, resulting in enhanced olefin separation. Accordingly, when the Cu nanoparticles were generated in MOIM+BF4-, the separation performance was twice that of neat ionic liquid and the mixed gas permeance increased from 6.9 to 12GPU due to facilitated olefin transport. This enhanced separation performance is attributed to both the free imidazolium ions and the positively polarized Cu nanoparticles, which favorably interact with the olefin molecules. The size and distribution of the generated Cu nanoparticles were confirmed by TEM and UV–vis spectra, respectively. The positive charge on the surface of the Cu nanoparticles was confirmed by investigating the binding energy using XPS.