Ionic Liquid Uptake Research Articles

Facile Ionization of the Nanochannels of Lamellar Membranes for Stable Ionic Liquid Immobilization and Efficient CO2 Separation.

Two-dimensional (2D) lamellar membranes, with highly ordered nanochannels between the adjacent layers, have revealed potential application prospects in various fields. To separate gases with similar kinetic diameters, intercalation of a functional liquid, especially an ionic liquid (IL), into 2D lamellar membranes is proved to be an efficient method due to the capacity of imparting solubility-based separation and sealing undesired defects. Stable immobilization of a high content of liquid is challenging but extremely required to achieve and maintain high separation performance. Herein, we describe the intercalation of a typical IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), into the ionized nanochannels of sulfonated MXene lamellar membranes, where the sulfonate groups are anchored onto MXene nanosheets through a facile method based on metal-catechol chelating chemistry. Thanks to the intrinsic benefits of MXene as building blocks and the decorated sulfonate groups, the optimal membrane possesses adequate interlayer spacing (∼1.8 nm) and high IL uptake (∼47 wt %) and therefore presents a CO2 permeance of 519 GPU and a CO2/N2 selectivity of 210, outperforming the previously reported liquid-immobilized lamellar membranes. Moreover, the IL loss rate of the membrane within 7 days at elevated pressure (5 bar) is measured to be significantly decreased (from 43.2 to 9.0 wt %) after growing sulfonate groups on the nanochannel walls, demonstrating the excellent IL storage stability.

An ionic liquid enhanced gel polymer electrolyte for high performance lithium-metal batteries based on sulfurized polyacrylonitrile cathode

Sulfurized polyacrylonitrile (SPAN) with superior cyclic stability is considered a promising cathode material for lithium-metal batteries (LMBs). However, the research on electrolyte system compatible with both cathode and anode remains limited currently. In this work, an ionic liquid enhanced gel polymer electrolyte (IL-GPE) with a freestanding fibrous structure is proposed for the highly stable LMBs. The polymer electrolyte shows uniform morphology with an average fiber diameter of 400 nm and high ionic liquid uptake. An ionic conductivity of 6.25 × 10−4 S cm−1 and an oxidative stability over 4.7 V is achieved. The addition of ionic liquid promotes uniform Li ions flux, leading to a compact electrodeposition of large Li particles. Meanwhile, the SPAN delivers a high reversible capacity of 1080 mAh g−1 after 200 cycles at 0.8 A g−1 without capacity fading. The decent rate capability performance demonstrates the fast ion transport property of IL-GPE. This work provides helpful reference for the development of electrolyte system suitable for Li||SPAN battery.

Influence of Mixed Imide Composition and Thermal Annealing on Ionic Liquid Uptake and Conductivity of Polyimide-Poly(ethylene glycol) Segmented Block Copolymer Membranes.

Understanding the impact of different bridging groups in the two-step polymerization of poly(ethylene glycol) (PEG)-incorporated polyimide (PI) materials is significant. It is known that the proton exchange membranes (PEMs) used in industry today can experience performance degradation under rising temperature conditions. Many efforts have been devoted to overcoming this problem by improving the physical and mechanical properties that extend the hygrothermal life of a PEM. This work examines the effect of oxygenated and fluorinated bridging anhydrides in the production of PI-PEG PEMs. It is shown that the dianhydride identity and the amount incorporated in the synthesis influences the properties of the segmented block copolymer (SBC) membranes, such as increased ionic liquid uptake (ILU), enhanced conductivity and higher Young’s modulus favoring stiffness comparable to Nafion 115, an industrial standard. Investigations on the ionic conductivity of PI-PEG membranes were carried out to determine how thermal annealing would affect the material’s performance as an ion-exchange membrane. By applying a thermal annealing process at 60 °C for one hour, the conductivities of synthesized segmented block copolymer membranes values were increased. The effect of thermal annealing on the mechanical properties was also shown for the undoped SBC via measuring the change in the Young’s modulus. These higher ILU abilities and mechanical behavior changes are thought to arise from the interaction between PEG molecules and ethylammonium nitrate (EAN) ionic liquid (IL). In addition, higher interconnected routes provide a better ion-transfer environment within the membrane. It was found that the conductivity was increased by a factor of ten for undoped and a factor of two to seven for IL-doped membranes after thermal annealing.

Plasticized 3D-Printed Polymer Electrolytes for Lithium-Ion Batteries

In the current research, we developed and printed by fused-filament fabrication polylactide-polyethylene-oxide blended membranes. The influence of relative content of polymers on the ease of extrusion and printing processes was studied. Ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide (Pyr14TFSI) with dissolved LiTFSI salt was infused into the membranes to produce free-standing films of quasi-solid polymer electrolytes. The printed membranes were characterized by ESEM, DSC, XPS, NMR and EIS methods. Neat-printed PLA (polylactide) membrane exhibited poor wetting and low uptake of ionic liquid. However, the XPS tests of 3D-printed PLA-PEO membrane infused with LiTFSI solvated ionic liquid show evidence of the interaction between lithium cations with both, PEO (polyethylene oxide) and PLA. The measurements of diffusion coefficients by PGSE-NMR suggest that the Li+ ions are coordinated by the PEO segments in the polymer blend. Increase of the PEO content at the expense of PLA polymer, leads to more than one order of magnitude improvement of bulk conductivity, approaching 0.2 mS cm−1 at 60

Effect of Increased Ionic Liquid Uptake via Thermal Annealing on Mechanical Properties of Polyimide-Poly(ethylene glycol) Segmented Block Copolymer Membranes.

Proton exchange membranes (PEMs) suffer performance degradation under certain conditions—temperatures greater than 80 °C, relative humidity less than 50%, and water retention less than 22%. Novel materials are needed that have improved water retention, stability at higher temperatures, flexibility, conductivity, and the ability to function at low humidity. This work focuses on polyimide-poly(ethylene glycol) (PI-PEG) segmented block copolymer (SBC) membranes with high conductivity and mechanical strength. Membranes were prepared with one of two ionic liquids (ILs), either ethylammonium nitrate (EAN) or propylammonium nitrate (PAN), incorporated within the membrane structure to enhance the proton exchange capability. Ionic liquid uptake capacities were compared for two different temperatures, 25 and 60 °C. Then, conductivities were measured for a series of combinations of undoped or doped unannealed and undoped or doped annealed membranes. Stress and strain tests were performed for unannealed and thermally annealed undoped membranes. Later, these experiments were repeated for doped unannealed and thermally annealed. Mechanical and conductivity data were interpreted in the context of prior small angle X-ray scattering (SAXS) studies on similar materials. We have shown that varying the compositions of polyimide-poly(ethylene glycol) (PI-PEG) SBCs allowed the morphology in the system to be tuned. Since polyimides (PI) are made from the condensation of dianhydrides and diamines, this was accomplished using components having different functional groups. Dianhydrides having either fluorinated or oxygenated functional groups and diamines having either fluorinated or oxygenated diamines were used as well as mixtures of these species. Changing the morphology by creating macrophase separation elevated the IL uptake capacities, and in turn, increased their conductivities by a factor of three or more compared to Nafion 115. The stiffness of the membranes synthesized in this work was comparable to Nafion 115 and, thus, sufficient for practical applications.

Sea-island nanostructured polyvinylidene fluoride/zeolitic imidazolate framework-8 polyelectrolyte for high-performance all-solid-state supercapacitors

All-solid-state supercapacitors with high power density, lightweight and durability have shown enormous potential for sustainable energy applications. However, the insufficient mechanical and electrochemical properties of polyelectrolyte membranes restrict their energy storage performances. Here, we report a sea-island nanostructured polyvinylidene fluoride/zeolitic imidazolate framework-8 (PVDF/ZIF-8) polyelectrolyte with superior mechanical and ionic properties for boosting energy storage performances of the supercapacitors. ZIF-8 nanoparticles with 8% content were dispersed uniformly into PVDF substrate and improved ionic liquid uptake of the membrane (from 42% to 74%) because of its high surface area (764 m2 g−1) and porous structure (pore width of 2.1 nm). Meanwhile, plastication effect of ZIF-8 materials improved mechanical properties of the membrane with tensile modulus of 2.88 MPa and break elongation of 11.6%. The PVDF/ZIF-8 based supercapacitors delivered a high specific capacitance of 156 F g−1 at current density of 1 A g−1 and showed good rate capability at current densities from 1 to 10 A g−1. The device could keep working over 20000 cycles at 1 A g−1 with capacitance retention of 91.7%, showing excellent cycling stability and enormous potential for applications. This work sheds light on design of novel polyelectrolyte membranes with high electrochemical and mechanical properties for long life energy storage devices.

100 MeV O7+ ion irradiation induced electrochemical enhancement in NiBTC metal-organic framework based composite polymer electrolytes incorporated with ionic liquid

Nickel 1,3,5-benzenetricarboxylate (NiBTC) metal-organic framework (MOF), has been synthesized by solvothermal method and dispersed in Poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) polymer. The composite polymer electrolyte membranes were irradiated with 100 MeV O7+ swift heavy ion (SHI) at different fluences and ionic liquid (IL) BMIMBF4 has been incorporated after irradiation. Increasing % uptake of IL has been observed upon IL incorporation as SHI irradiation can enlarge the micropore volumes of NiBTC-MOF by inducing missing linker defects. FTIR spectra depict shifting of carboxylate vibrational modes with increasing fluence suggesting elongation of metal-linker molecular bonds in NiBTC-MOF due to interaction of BF4- anion of IL with unsaturated Ni metal nodes with increasing uptake of IL. Non-Debye relaxation ion dynamics has been revealed from dielectric modulus spectra and optimum ionic conductivity of 9.9 × 10−3 Scm−1 is achieved for the nanocomposite membrane at the fluence of 3.3 × 1012 ions cm−2 at 380 K. The frequency dependent AC conductivity increases with increasing fluence due to higher IL uptake as well as chain scission of the polymer segments. The electrochemical stability of the nanocomposite membrane increases with increasing fluence and attains a maximum value of 6.1 V at 3.3 × 1012 ions cm−2.

Electrode-Impregnable and Cross-Linkable Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) Triblock Polymer Electrolytes with High Ionic Conductivity and a Large Voltage Window for Flexible Solid-State Supercapacitors.

We present cross-linkable precursor-type gel polymer electrolytes (GPEs) that have large ionic liquid uptake capability, can easily penetrate electrodes, have high ion conductivity, and are mechanically strong as high-performance, flexible all-solid-state supercapacitors (SC). Our polymer precursors feature a hydrophilic-hydrophobic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock main-chain structure and trifunctional silane end groups that can be multi-cross-linked with each other through a sol-gel process. The cross-linked solid-state electrolyte film with moderate IL content (200 wt %) shows a well-balanced combination of excellent ionic conductivity (5.0 × 10-3 S cm-1) and good mechanical stability (maximum strain = 194%). Moreover, our polymer electrolytes have various advantages including high thermal stability (decomposition temperature > 330 °C) and the capability to impregnate electrodes to form an excellent electrode-electrolyte interface due to the very low viscosity of the precursors. By assembling our GPE-impregnated electrodes and solid-state GPE film, we demonstrate an all-solid-state SC that can operate at 3 V and provides an improved specific capacitance (112.3 F g-1 at 0.1 A g-1), better rate capability (64% capacity retention until 20 A g-1), and excellent cycle stability (95% capacitance decay over 10 000 charge/discharge cycles) compared with those of a reference SC using a conventional PEO electrolyte. Finally, flexible SCs with a high energy density (22.6 W h kg-1 at 1 A g-1) and an excellent flexibility (>93% capacitance retention after 5000 bending cycles) can successfully be obtained.

Ionic Liquid Surface Treatment of Calcite for Improved Compatibility with Polyolefin Matrix

Preliminary surface treatment of crystalline marble powder filler with a dominatingly hydrophobic ionic liquid, namely triethylsulfonium-bis(trifluoromethylsulfonyl) imide has been employed to design a filler with improved compatibility towards non-polar polymer matrices, such as polyolefins. The maximum uptake of ionic liquid per 1g of marble powder was 132 mg. The surface coating of the crystalline phases has been proved by XRD and FTIR spectroscopy, making our method useful in designing fillers with improved dispersibility/ compatibility in/with polyolefins. The floating test method has proved the efficiency of the alkylsulfonium ionic liquid in hydrophobization of the crystalline calcite-rich phase, thus proving useful in obtaining composites with improved properties.

High-fidelity bioelectronic muscular actuator based on porous carboxylate bacterial cellulose membrane

Human-friendly electronic products, such as smart mobile phones, soft haptic devices, wearable electronics, and implantable or disposal biomedical devices, will require the use of high-performance durable soft electroactive actuators with eco-friendly, biocompatible, and biodegradable functionalities. Here, we report a high-fidelity bioelectronic muscular actuator based on porous carboxylate bacterial cellulose (CBC) membranes fabricated using the facile zinc oxide (ZnO) particulate leaching (PL) method. The proposed CZ-PL muscular actuator exhibits large deformation, low actuation voltage, fast response, and high-durability in open air environment. In particular, the CZ-PL membrane shows a dramatic increase in the ionic liquid uptake ratio, ionic exchange capacity, and ionic conductivity of up to 70.63%, 22.50%, and 18.2%, respectively, for CBC, resulting in a 5.8 times larger bending deformation than that of the pure CBC actuator. The developed high-performance CZ-PL muscular actuator can be a promising candidate for meeting the tight requirements of human-friendly electronic devices such as wearable devices, biomimetic robots, and biomedical active devices.

Critical review of ionic liquids for the pretreatment of lignocellulosic biomass

Ionic liquids have been the subject of active research over the course of the last decade and have in the past been touted as one of the most promising technologies for revolutionising the chemical and petro-chemical industries. The sheer abundance of potential ionic liquid structures coupled with their tuneable physico-chemical properties has endeared ionic liquids to the scientific community across a broad range of disciplines with potential applications that include pharmaceuticals, electrolytes, thermal energy storage media and liquid mirror telescopes. Within the context of a biorefinery for the production of biofuels and other bio-based products from renewable resources, the unique abilities of some ionic liquids to selectively dissolve biomass components or whole native biomass have been demonstrated. This ability has sparked extensive investigations of ionic liquids for the pretreatment of different biomass types, particularly for the production of cellulosic biofuels. However, the esoteric nature of ionic liquids persists and constructing a fundamental framework for correlating ionic liquid structures with useful applications remains a significant challenge. In addition to the above, the more practical challenges of toxicity, high costs, high viscosities, low solids loading and complex recycling are key factors hindering the wide-scale uptake of ionic liquids as pretreatment solvents in a commercial biorefinery. This critical review provides insights from academic studies and the implications thereof for elevating ionic liquids from the status of ‘promising’ to ‘commercialisable’ in the pretreatment of biomass. It is vital that key hurdles for the commercialisation of ionic liquids in the form of high costs, high viscosities, poor water tolerance, toxicity, low solids loading and recovery/recycling be addressed.

Interlayer configuration of ionic liquids in a Ca-montmorillonite as evidenced by FTIR, TG-DTG, and XRD analyses

Ionic liquids (ILs) have attracted much attention in the scientific community during the past two decades. However, studies of interactions between Earth materials and ILs have been limited. In this study, the uptake and interlayer configuration of ILs on a high charge Ca-montmorillonite (MMT) were systematically studied using TG-DTG, FTIR, and XRD analyses. The intercalation protected the ILs from thermal decomposition, resulted in an increase in their thermal stability in comparison to ILs adsorbed on the surfaces. The results from TG-DTG, FTIR, and XRD all pointed to a change in mechanisms and interlayer configurations as the chain length, input amounts, and initial concentrations of ILs changed. A higher decomposition temperature in TG analyses and a large blue shift of selected FTIR bands agreed well with the cation exchange mechanism at lower IL loading levels. Accompanying cation exchange the interlayer water was completely removed. Hydrophobic interactions and admicelle adsorption were responsible for IL uptake beyond the cation exchange capacity of the MMT. A pseudo-trilayer configuration was suggested based on XRD analyses for the intercalation of ILs with a chain length of 12 carbons at the sorption maximum and that of 16 carbons at medium sorption levels. A paraffin-like conformation with an almost vertical orientation was suggested for the configuration of IL with a chain length of 16 carbons in the interlayer of MMT at the sorption maximum.

Modification of a Ca-montmorillonite with ionic liquids and its application for chromate removal

Ionic liquids (ILs), due to their low vapor pressure, have been explored as green solvents for organic synthesis. In this study, the uptake of ILs on a high charge Ca-montmorillonite (MMT) and the use of the IL-modified MMT for the removal of anionic contaminants from water were systematically studied. Uptake of ILs by MMT was exclusively resulted from a cation exchange mechanism when the initial IL concentrations were less than the critical micelle concentration (CMC) and the sorbed ILs formed a monolayer conformation on the surface of MMT. When the initial IL concentrations were greater than the CMC, both cation exchange and hydrophobic interactions were responsible for the IL uptake. The IL molecules formed admicelles and the surface charge was reversed to positive balanced by counterion Cl− when the IL loading was higher than the cation exchange capacity of the mineral. The modified MMT could remove chromate from water instantaneously, with an adsorption capacity of 190mmol/kg and a 99.5% removal efficiency at an initial chromate concentration of 2.6mmol/L. These features could further expand the application of ILs and enable IL-modified MMT to be used as inexpensive sorbents for the removal of chromate and other oxyanions from water.

Swelling and Stability of Polyelectrolyte Multilayers in Ionic Liquid Solutions

Swelling of polyelectrolyte multilayers with aqueous solution of ionic liquid (IL) is examined with a dissipative quartz crystal microbalance. Multilayers are prepared with different combinations of polyelectrolyte, employing PEI(PSS/PAH)4PSS and PEI(PSS/PDADMAC)4PSS. An enhancement of mass coverage and dissipation is found for films in contact with aqueous solution of IL, i.e., 1-hexyl-3-methylimidazolium chloride and 1-methyl-3-methylimidazolium chloride, suggesting incorporation of IL, accompanied by film swelling. Swelling increases with increasing IL concentration. It is strictly reversible up to a stability limit of IL concentration, above which irreversible layer decomposition starts. Each swelling step can be divided into a fast and a slow process, resulting from IL uptake and chain reorganization or layer decomposition, respectively. While absolute IL uptake and swelling limits differ, the concentration dependence is similar in all systems investigated. The swelling is attributed to hydrophobic interactions, since we find a correlation of the swelling with hydrophobicity of IL.

Interactions of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid with Alumina Nanoparticles and Organic Solvents Studied by Infrared Spectroscopy

The interface between 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EmIm][OTf]) ionic liquid (IL) supported on alumina nanoparticles and organic solvents (ethanol, tetrahydrofuran and acetonitrile) has been investigated using infrared (IR) spectroscopy. The investigations of these liquid–solid interfaces were preceded by separate studies of the IL in the different solvents and the IL supported on the alumina nanoparticles. IR analyses of the solvent–[EmIm][OTf] mixtures indicated that the triflate anion interacts differently with the three solvents. Comparison of the spectra of the IL supported on alumina with those measured for the corresponding solvent–IL mixtures indicates an interaction between the SO3 group of the anion and the alumina surface. In the organic solvent–IL–alumina systems, similar interactions between the IL and the oxide surface occur. The behavior of the IL/alumina interfaces was found to be consistent with a model where the ionic liquid structure is perturbed due to charge neutralization in a thin layer at the interface. Qualitative studies of the kinetics of adsorption and desorption of the IL in the organic liquid phases indicated that the choice of the organic solvent has a significant influence on these processes. Comparative studies with a commercial Pt on alumina catalyst possessing similar surface area showed that the IL uptake strongly increases in the presence of Pt on the alumina surface. Comparison of adsorption–desorption cycles of the IL measured for the alumina support and Pt on alumina revealed a much stronger interaction of the IL with the Pt surface than with the alumina.

The Effect of Ionic Liquid Uptake and Self-assembled Conductive Network Composite Layers on NafionTM based Ionic Polymer Metal Composite Electromechanical Bending Actuators

ABSTRACTIonic liquid (IL) is used as the working electrolyte in ionic polymer metal composite (IPMC) electromechanical bending actuators because of its high stability and conductivity, which are crucial for the consistency and speed of the actuation. Because the bending actuation is caused by the migration and accumulation of the cations and anions of the IL, it is clear that both the overall number of ions and the effectiveness of ion transport and accumulation play important roles in the actuation behavior. In this paper, the effect of enhancing the ion accumulation by the self-assembled conductive network composite (CNC) layers is investigated by comparing the bending behavior of actuators with and without CNC layers. In addition, IPMC actuators with various IL uptakes are also tested in order to study the dependence of the bending performance on the amount of the ions available. It is found that, with the CNC layers, the maximum bending curvature of the actuator increases with increased IL, which shows the crucial role played by the IL. However, under the same conditions, the performance improvement of actuators without CNC layers saturates when the IL uptake reaches around 10% wt. This demonstrates the role of the CNC layers to provide a porous electrode with increased capacitance that thus accommodates accumulation of more ions near the electrodes, which in turn boosts the overall bending curvature of the actuator.

A highly aromatic and sulfonated ionomer for high elastic modulus ionic polymer membrane micro-actuators

A high modulus, sulfonated ionomer synthesized from 4,6-bis(4-hydroxyphenyl)-N,N-diphenyl-1,3,5-triazin-2-amine and 4,4′-biphenol with bis(4-fluorophenyl)sulfone (DPA-PS:BP) is investigated for ionic polymer actuators. The uniqueness of DPA-PS:BP is that it can have a high ionic liquid (IL) uptake and consequently generates a high intrinsic strain response, which is >1.1% under 1.6 V while maintaining a high elastic modulus (i.e. 600 MPa for 65 vol% IL uptake). Moreover, such a high modulus of the active ionomer, originating from the highly aromatic backbone and side-chain-free structure, allows for the fabrication of free-standing thin film micro-actuators (down to 5 µm thickness) via the solution cast method and focused-ion-beam milling, which exhibits a much higher bending actuation, i.e. 43 µm tip displacement and 180 kPa blocking stress for a 200 µm long and 5 µm thick cantilever actuator, compared with the ionic actuators based on traditional ionomers such as Nafion, which has a much lower elastic modulus (50 MPa) and actuation strain.

A High-Modulus Electroactive Polymer Acting as a Robust Ionomer for Ionic Micro-Actuators

ABSTRACTA high modulus, sulfonated polymer synthesized from one-to-one ratio 4,6-bis(4-hydroxyphenyl)-N, N-diphenyl-1,3,5-triazin-2-amine and 4,4′-biphenol with bis(4-fluorophenyl) sulfone (DPA-PS:BP) is exploited as an ionomer for micro-ionic actuators. A unique and attractive feature of the ionomer is that it can contain high amounts of ionic liquid (IL) as an electrolyte while maintaining a high elastic modulus (i.e 600 MPa for 150 wt% uptake), which is more than one order of magnitude higher than the state-of-the-art of ionomers with working electrolytes. Such a high modulus makes it possible for the ionomer to be fabricated into micro-actuators with high uptake of ILs and low operation voltage (< 4 V), in various free standing forms with ion milling techniques, which are attractive for MEMS applications. As an initial demonstration of a DPA-PS:BP based ionic micro-actuator, a cantilever (200 μm x 33 μm x 5 μm) is manufactured by Focused Ion Beam (FIB) and characterized. Under the voltage of 1.6 V, the bending actuator exhibits an intrinsic strain from the active ionomer of 1.1% and a corresponding blocking force of 27 μN.

Charge dynamics and bending actuation in Aquivion membrane swelled with ionic liquids

The actuation strain and speed of ionic electroactive polymer (EAP) actuators are mainly determined by the charge transport through the actuators and excess ion storage near the electrodes. We employ a recently developed theory on ion transport and storage to investigate the charge dynamics of short side chain Aquivion® (Hyflon®) membranes with different uptakes of ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). The results reveal the existence of a critical uptake of ionic liquids above which the membrane exhibits a high ionic conductivity (σ > 5×10−2 mS/cm). Especially, we investigate the charge dynamics under voltages which are in the range for practical device operation (∼1 V and higher). The results show that the ionic conductivity, ionic mobility, and mobile ion concentration do not change with the applied voltage below 1 V (and for σ below 4 V). The results also show that bending actuation of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chains improve the electromechanical coupling between the excess ions and the membrane backbones, while not affecting the actuation speed.

Thermal stability and moisture uptake of 1-alkyl-3-methylimidazolium bromide

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, (BMIM)Br, and 1-n-octyl-3-methylimidazolium bromide, (OMIM)Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition tempera- ture, previously determined from fast scan TG experi- ments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 C interval in the range 533-573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of (BMIM)Br and (OMIM)Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol -1 , respectively. The moisture absorption kinetics of these ILs at 25 C and 30% relative humidity (RH) and at 85 C and 85% RH were also stud- ied. Water uptake of ILs exposed at 25 C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 C/85%RH fortuitously fit into the Henderson-Pabis model.