Hygroscopic Ionic Liquids Research Articles

Application of High-Surface Tension and Hygroscopic Ionic Liquid-Infused Nanostructured SiO2 Surfaces for Reversible/Repeatable Anti-Fogging Treatment

Anti-fogging coatings/surfaces have attracted much attention lately because of their practical applications in a wide variety of engineering fields. In this study, we successfully developed transparent anti-fogging surfaces using a non-volatile and hygroscopic ionic liquid (IL), bis(hydroxyethyl)dimethylammonium methanesulfonate ([BHEDMA][MeSO3]), with a high surface tension (HST, 66.4 mN/m). To prepare these surfaces, a layer of highly transparent, superhydrophilic silica (SiO2) nano-frameworks (SNFs) was first prepared on a glass slide using candle soot particles and the subsequent chemisorption of tetraethoxysilane (TEOS). This particulate layer of SNFs was then used as the support for the preparation of the [BHEDMA][MeSO3] layer. The resulting IL-infused SNF-covered glass slide was highly transparent, superhydrophilic, hygroscopic, and had self-healing and reasonable reversible/repeatable anti-fogging/frosting properties. This IL-infused sample surface kept its excellent anti-fogging performance in air for more than 8 weeks due to the IL’s non-volatile, HST, and hygroscopic nature. In addition, even if the water absorption limit of [BHEDMA][MeSO3] was reached, the anti-fogging properties could be fully restored reversibly/repeatably by simply leaving the samples in air for several tens of minutes or heating them at 100 °C for a few minutes to remove the absorbed water. Our IL-based anti-fogging surfaces showed substantial improvement in their abilities to prevent fogging when compared to other dry/wet (super)hydrophobic/(super)hydrophilic surfaces having different surface geometries and chemistries.

Trace Water Effects on Crystalline 1-Ethyl-3-methylimidazolium Acetate.

Spontaneous room-temperature crystallization of 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was observed upon removal of trace water. Sample purity was confirmed using analytical nuclear magnetic resonance spectroscopy to ensure that trace water or other contaminants did not produce this observation. Raman spectroscopy and simultaneous quartz crystal microbalance/infrared spectroscopy measurements were used to study molecular reorganization during crystallization and decrystallization using trace water in the form of atmospheric moisture. These experimental results were supplemented with density functional theory calculations that indicate imidazolium cation ring stacking and side chain clustering with an exclusive arrangement of the acetate anion in the cation ring plane upon water removal. Crystal structure formation was confirmed using two-dimensional wide-angle X-ray scattering. This natural crystallization is attributed to the removal of trace water over extended periods of time and calls attention to the molecular-level role of water in the structure of hygroscopic ionic liquid systems.

Flexible Zinc-Air Batteries with Ampere-Hour Capacities and Wide-Temperature Adaptabilities.

Flexible Zn-air batteries (FZABs) have significant potentials as efficient energy storage devices for wearable electronics because of their safeties and high energy-to-cost ratios. However, their application is limited by their short cycle lives, low discharge capacities per cycle, and high charge/discharge polarizations. Accordingly, herein, a poly(sodium acrylate)-polyvinyl alcohol (PANa-PVA)-ionic liquid (IL) hydrogel (PANa-PVA-IL) is prepared using a hygroscopic IL, 1-ethyl-3-methylimidazolium chloride, as an additive for twin-chain PANa-PVA. PANa-PVA-IL exhibits a high conductivity of 306.9mScm-1 and a water uptake of 2515 wt% at room temperature. Moreover, a low-cost bifunctional catalyst, namely, Co9 S8 nanoparticles anchored on N- and S-co-doped activated carbon black pearls 2000 (Co9 S8 -NSABP), is synthesized, which demonstrates a low O2 reversibility potential gap of 0.629V. FZABs based on PANa-PVA-IL and Co9 S8 -NSABP demonstrate high discharge capacities of 1.67mAhcm-2 per cycle and long cycle lives of 330h.Large-scale flexible rechargeable Zn-air pouch cells exhibit total capacities of 1.03Ah and energy densities of 246Whkgcell -1 . This study provides new information about hydrogels with high ionic conductivities and water uptakes and should facilitate the application of FZABs in wearable electronics.

Thermo‐Adaptive Block Copolymer Structural Color Electronics

AbstractFlexible electronics that enable the visualization of thermal energy have significant potential for various applications, such as thermal diagnosis, sensing and imaging, and displays. Thermo‐adaptive flexible electronic devices based on thin 1D block copolymer (BCP) photonic crystal (PC) films with self‐assembled periodic nanostructures are presented. By employing a thermo‐responsive polymer/non‐volatile hygroscopic ionic liquid (IL) blend on a BCP film, full visible structural colors (SCs) are developed because of the temperature‐dependent expansion and contraction of one BCP domain via IL injection and release, respectively, as a function of temperature. Reversible SC control of the bi‐layered BCP/IL polymer blend film from room temperature to 80 °C facilitates the development of various thermo‐adaptive SC flexible electronic devices including pixel arrays of reflective‐mode displays and capacitive sensing display. A flexible diagnostic thermal patch is demonstrated with the bi‐layered BCP/IL polymer blend enabling the visualization of local heat sources from the human body to microelectronic circuits.

Chlorine drying with hygroscopic ionic liquids

The chlorine (Cl2) drying technology using ionic liquids (ILs) as absorbents was proposed for the first time and systematically investigated from the molecular level scaled up to the industrial level. The hygroscopic IL [EMIM][CH3SO3] was screened as a suitable absorbent from 238 potential IL candidates consisting of 14 cations and 17 anions, by calculating the Cl2 and H2O solubility and separation selectivity of Cl2 to H2O in different ILs based on the COSMO-RS model. The microscopic atomic and molecular insights into the separation mechanisms were deeply revealed by using COSMO-RS model analyses (i.e., σ-profiles, σ-potentials, excess enthalpies, entropies, and Gibbs free energies) and quantum chemistry calculation (binding energies and weak interaction analyses). The Cl2 solubility in pure IL and H2O + IL systems were predicted by the COSMO-RS model, and the results agree with the microscopic mechanism identification. Moreover, the strict equilibrium stage model employed with the COSMO-RS model parameters was built to perform the process simulation, and continuous Cl2 drying with ILs was conceptually designed and optimized at industrial scale. It was confirmed that [EMIM][CH3SO3] is a very promising absorbent leading to a less IL amount, a much lower energy consumption than the other IL [EMIM][BF4], which has a very bright industrialization potential used for Cl2 drying technology.

Gas Drying Using Supported Ionic Liquids

Supported ionic liquids are promising pseudo-adsorbents for gas drying processes. They are produced by impregnation of hygroscopic ionic liquids with low vapor pressures on silica surfaces. A screening of potential alternatives to [EMIM][MeSO3] revealed that [EMIM][TFA] is sufficiently hygroscopic but not thermally stable enough for technical use. [EMIM]Cl shows, compared to [EMIM][MeSO3], a higher affinity for water absorption, but is less stable as well as corrosive. [EMIM][OTF] shows high thermal stability, but has an insufficient low activity coefficient of water, so that [EMIM][MeSO3] remains most promising. Water sorption isotherms and measurements of breakthrough curves in a bench scale fixed-bed adsorber confirmed, that depending on the operating conditions, the capacity for water can be increased in a supported system of [EMIM][MeSO3] impregnated on Silica 90, compared to adsorption at the pure silica surface. Exceptionally for medium to low partial pressures of water, supported systems appear to be favourable for adsorption processes. The shapes of the breakthrough curves of pure silica and the supported system are similar, what indicates similar or only slightly increased mass transport resistances due to the impregnation.

Examining the effects of storage on the initiation behaviour of ionic liquids towards the cure of epoxy resins

Four structurally related ionic liquids (1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium diethyl phosphate, 1-ethyl-3-methylimidazolium dicyanamide, and 1-ethyl-3-methylimidazolium thiocyanate) are examined for their storage characteristics and the effect on their ability to initiate the cure of epoxy resins. At ambient temperature, epoxy formulations containing 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium thiocyanate display marked colour changes to yield dark red samples with greatly increased viscosity after one day; after six days both samples have undergone vitrification. The epoxy formulation containing 1-ethyl-3-methylimidazolium acetate continued to polymerise even at sub-zero temperatures. Storage in dark bottles retarded the reaction during the 30-minute period that the sample is removed from the freezer prior to an aliquot being taken, but once the autocatalytic low temperature reaction has started, the dark glass no longer provides effective protection. Samples of 1-ethyl-3-methylimidazolium dicyanamide/epoxy were also stored and sampled in the same manner, but no differences were exhibited between the samples in clear and dark brown glass bottles. Infrared and nuclear magnetic resonance studies confirmed that the hygroscopic ionic liquids pick up water readily (coordinating to the H atom at the 2-position on the imidazolium ring), but once dried the initiating ability is lost.

PROPERTIES OF 1-BUTYL-3-METHYLIMIDAZOLIUM BROMIDE IONIC LIQUID AND ITS BLENDS WITH WATER AND BROMIDES OF SILVER, COPPER AND TANTALUM

Ionic liquids with N,N¢-dialkylimidazolium cation characterized now as "green" solvents are investigated intensively to find their practical application. In this research the physical-chemical, electrochemical and corrosion properties of 1-butyl-3-methylimidazolium bromide (BMImBr) and its blends with water and bromides of silver (I), cupper (II) and tantalum (V) were studied. BMImBr is a hygroscopic ionic liquid and in depending on a water content can exists as a solid, liquid, metastable supercooled melt, and two-phase system – liquid and crystalline hydrate of BМImBr´0.5Н2О composition. At 1:1 components ratio the structural transformation of the melt (СН2О<50 mol%) « the solution (СН2О>50 мол.%) was observed. The BMImBr ionic liquid is a good solvent towards bromides of silver (I), cupper (II) and tantalum (V). These salts destroy the inter- and intramolecular interactions of BMImBr and generate the complex metal-containing ions with Br- anion of ionic liquid. As a result the glass temperature and the density increased, the melting point decreased and on isotherms of dynamic viscosity and specific electro conductivity a distinct minimum was observed at the low concentration range of the salt. Electrochemical window of BMImBr is 1.9 V and it is limited by bromide ions oxidation in the anodic potential range and by imidazolium cations reduction in the cathodic potential range. Additions of the water and the metals salt are an electrochemical active. In their presence the redox processes proceeds inside of the electrochemical window and the discharge-ionization process is the limiting steps. From IL studied the thin films of silver and copper can be deposited with good adhesion on metal substrates including tantalum and titanium. Investigated ionic liquids are a corrosive fluid, and corrosion of the metal increases dramatically in the presence of the same cations.

Characterization of Six Hygroscopic Ionic Liquids with Regard to Their Suitability for Gas Dehydration: Density, Viscosity, Thermal and Oxidative Stability, Vapor Pressure, Diffusion Coefficient, and Activity Coefficient of Water

Six hygroscopic ionic liquids (ILs), [DMIM][DMPO4], [EMIM][MeSO3], [EMIM][EtSO4], [EMIM][Et(EG)2SO4], [BMIM][BF4], and [choline][glycolate], were investigated with regard to their suitability as a drying agent for technical gas dehydration processes by absorption. Therefore, the density, viscosity, activity coefficient of water in the ILs, and the kinetic parameters of thermal and oxidative degradation were measured (if the respective values were not already reported in the literature). [EMIM][MeSO3] proved to be the most suitable candidate for industrial gas dehydration. This IL has a low activity coefficient, a high thermal and oxidation stability, an acceptably low viscosity as well as a very low vapor pressure. Thus, the influence of temperature on the activity coefficient of water and the diffusivity of water in this IL was also determined.

Continuous Gas Dehydration Using the Hygroscopic Ionic Liquid [EMIM][MeSO3] as a Promising Alternative Absorbent

AbstractContinuous gas drying experiments with the hygroscopic ionic liquid [EMIM][MeSO3] show that it can be a very promising alternative drying agent to the absorbent triethylene glycol (TEG) commonly used in industrial gas drying processes. The HTU/NTU model in combination with the correlations of Onda et al. for mass transfer coefficients can be applied for the design of an absorption process with [EMIM][MeSO3]. The major advantage of this ionic liquid (IL) is that well‐known problems associated with the regeneration of the absorbent TEG can be avoided using [EMIM][MeSO3] due to extremely low vapor pressure and possible regeneration with air. The drying capacity of the IL system is about two times higher compared to TEG. Hence, a simple plant design comparable to that of industrial adsorption plants might be applied.

Dehumidification of air using liquid membranes with ionic liquids

This paper presents application of the hygroscopic ionic liquids, such as 1-ethyl-3-methylimidazolium ethylsulfate, 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium tetrafluoroborate, for the membrane-based air dehumidification. Liquid membranes, supported by the hydrophobic porous membrane, were prepared and their dehumidification efficiency was evaluated in terms of the water recovery rate and water vapor permeability. The performance of supported liquid membranes, composed of ionic liquid, was higher when compared to that, containing triethylene glycol. Ionic liquids showed recovery of water from 80%RH humid air as high as 10g/h.The permeabilities of water vapor through the ionic liquids were 26,000–46,000 Barrer and the separation factor to the air was over 1000. These measured permeabilities were compared to that predicted by the solution diffusion mechanism, which was supported by the adsorption, diffusivity and viscosity measurements of the liquids. It was demonstrated that solution–diffusion mechanism well describes transport of air through the ionic liquid membrane and with further considerations can be applied for the description of water vapor transport in ILs.

Water-clustering in hygroscopic ionic liquids—an implicit solvent analysis

Most ionic liquids are known to be hygroscopic to varying degrees, and that can be detrimental or useful depending upon the application in question. Water can accumulate slowly over hours or days to saturation levels corresponding to the humidity level. When designing or deploying a new ionic liquid it is important to be able to estimate its maximum moisture absorbing ability at the temperature and pressure of its operation. With this goal in mind we have carried out computational studies on three ionic liquid systems based on [BF(4)](-), [PF(6)](-), and [Tf(2)N](-) anions and 1-alkyl-3-methyl-imidazolium ([C(n)mim](+)) cations within an implicit solvent formalism. For highly hygroscopic systems like [C(n)mim][BF(4)] we find that non-iterative calculations with single water molecules can lead to significant underestimation of the maximum moisture content, while iterative calculations can result in miscibility behavior qualitatively different from experimental observations. On the other hand, the inclusion of small hydrogen-bonded water-clusters up to an appropriately chosen size is shown to yield better quantitative agreements with experimentally observed water uptake. Additionally, such calculations appear consistent with a number of thermodynamically interesting phase behaviors, including limited-solubility to full-miscibility transitions as a function of temperature and as a function of the alkyl chain length of the imidazolium cation. For hydrophobic systems like [C(n)mim][PF(6)] and [C(n)mim][Tf(2)N] the computed solubility (for each n) is found to have a smooth convergence behavior as a function of the largest cluster-size considered with the results for the larger clusters being close to that obtained by iterative calculations with single water molecules.

Liquid−Vapor Equilibrium of the Systems Butylmethylimidazolium Nitrate−CO2 and Hydroxypropylmethylimidazolium Nitrate−CO2 at High Pressure: Influence of Water on the Phase Behavior

Ionic liquids (IL) are receiving increasing attention due to their potential as "green" solvents, especially when used in combination with SC-CO2. In this work liquid-vapor equilibria of binary mixtures of CO2 with two imidazolium-based ionic liquids (IL) with a nitrate anion have been experimentally determined: butylmethylimidazolium nitrate (BMImNO3) and hydroxypropylmethylimidazolium nitrate (HOPMImNO3), using a Cailletet apparatus that operates according to the synthetic method. CO2 concentrations from 5 up to 30 mol % were investigated. It was found that CO2 is substantially less soluble in HOPMImNO3 than in BMImNO3. Since these ILs are very hygroscopic, water easily can be a major contaminant, causing changes in the phase behavior. In case these Ils are to be used in practical applications, for instance, together with CO2 as a medium in supercritical enzymatic reactions, it is very important to have quantitative information on how the water content will affect the phase behavior. This work presents the first systematic study on the influence of water on the solubility of carbon dioxide in hygroscopic ILs. It was observed that the presence of water reduces the absolute solubility of CO2. However, at fixed ratios of CO2/IL, the bubble point pressure remains almost unchanged with increasing water content. In order to explain the experimental results, the densities of aqueous mixtures of both ILs were determined experimentally and the excess molar volumes calculated.

Surface tensions of imidazolium based ionic liquids: Anion, cation, temperature and water effect

This work addresses the experimental measurements of the surface tension of eight imidazolium based ionic liquids (ILs) and their dependence with the temperature (288–353 K) and water content. The set of selected ionic liquids was chosen to provide a comprehensive study of the influence of the cation alkyl chain length, the number of cation substitutions and the anion on the properties under study. The influence of water content in the surface tension was studied for several ILs as a function of the temperature as well as a function of water mole fraction, for the most hydrophobic IL investigated, [omim][PF 6], and one of the more hygroscopic IL, [bmim][PF 6]. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values.

Ethylammonium Acetate as a Mobile Phase Modifier for Reversed Phase Liquid Chromatography

We have synthesized the low melting hygroscopic ionic liquid ethylammonium acetate (EAA) and characterized a concentrated solution of EAA as a reversed phase mobile phase replacement for organic solvents like methanol. This solution of EAA acts like an organic solvent with a polarity parameter (P’=6.0) similar to methanol (P’=5.1) but less than water (P’=10.2). A test mixture of salicylate, nitrofurantoin, and acetophenone was separated in this order on C1, C4, and C18 columns using an EAA modified aqueous mobile phase. On a C-18 column, the reduction in retention factor for acetophenone from about 20 to 2 as the % EAA is raised from 20–80% is similar to the same trend found using methanol. However, the retention order using methanol is first nitrofurantoin, then salicylate, and finally acetophenone. Log retention factor (k) versus the volume fraction of either EAA or methanol plots were linear indicating the solvent strength parameter for EAA was about 85% of that for methanol. Despite the relatively high viscosity of EAA, plate count values averaged only about 15% less for EAA as compared to methanol using the same mobile phase composition and could be raised by either working at a temperature above ambient or reducing the flow rate. EAA as a modifier allowed for faster separations of water-soluble vitamins on a reversed phase column designed for totally 100% aqueous mobile phases.

EuIII Luminescence in a Hygroscopic Ionic Liquid: Effect of Water and Evidence for a Complexation Process

AbstractThe spectroscopic characteristics (excitation, emission and lifetime) of EuIII dissolved in 1‐methyl‐3‐butylimidazolium bis(trifluoromethanesulfon)imide (BumimTf2N) are reported. In a first series of experiments, the effect of the presence of water in BumimTf2N was examined. It appears that non‐degassed solutions are most probably inhomogeneous, displaying large water clusters leading to an intense diffusion of the red light of an He:Ne laser. In these samples, the Eu emission spectrum is close to that observed in slightly acidic aqueous solutions. In contrast, when the samples were degassed the solution appeared homogeneous and water can be considered as a competitive ligand for the first coordination sphere of Eu. In a subsequent series of experiments, tetrabutylammonium chloride (TBACl) was added to the solution and the resultant species investigated. The ensuing enhancement in the metal‐centered luminescence has been interpreted in terms of changes in the inner coordination sphere of the EuIII ion and possible structures are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)