Ionic Network Research Articles

The role of the symmetry and the flexibility of the anion on the characteristics of the nanostructures and the viscosities of ionic liquids

The transport properties of ionic liquids (ILs) are crucial properties in view of their applications in electrochemical devices. One of the most important advantages of ILs is that their chemical–physical properties and consequently their bulk performances can be well tuned by optimizing the chemical structures of their ions. This will require elucidating the structural features of the ions that fundamentally determine the characteristics of the nanostructures and the viscosities of ILs. Here we showed for the first time that the “rigidity”, the order, and the compactness of the three-dimensional ionic networks generated by the anions and the cation head groups determine the formation and the sizes of the nanostructures in the apolar domains of ILs. We also found that the properties of ionic networks are governed by the conformational flexibility and the symmetry of the anion and/or the cation head group. The thermal stability of the nanostructures of ILs was shown to be controlled by the sensitivity of the conformational equilibrium of the anion to the change of temperature. We showed that the viscosity of ILs is strongly related to the symmetry and the flexibility of the constitute ions rather than to the size of the nanostructures of ILs. Therefore, the characteristics of the nanostructures and the viscosities of ILs, especially the thermal stability of the nanostructures, can be fine-tuned by tailoring the symmetry and the conformational flexibility of the anion.

Synthesis and characterization of thermoreversible K-Ionomers based on butyl rubber: a simple one-step crosslinking method and a novel crosslinking system

A simple one-step thermoreversible polymer crosslinking method and a novel reversible ionic crosslinking system (maleic anhydride and KOH) have been developed which is performed on high physical mechanical properties and valuable reversibility. The system involves the acid–base reaction of maleic anhydride with potassium hydroxide to form ionic thermoreversible cross-linking network. A series of ionic thermoreversible cross-linking butyl rubber which is called K-ionomers are obtained as a function of the ratio of KOH to maleic anhydride by simple one-step solution method. The ratio is held at 5:1, the degrees of neutralization is up to 70 % that reprocessibility is possible. X-ray diffraction (XRD) shows the presence of microphase-separated aggregates for K-ionomer that act as physical cross-links which are responsible for its outstanding mechanical property and valuable reversiblity. Very high mechanical property in tensile strength up to 5 Mpa was obtained. The reversibility of K-ionomers is investigated in detail by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Hot stage microscopy. ATR-FTIR results show a desired shift back from carboxylate reacted with carboxylic acid to cyclic anhydrides and KOH depending on heating. Hot stage microscopy shows that the reprocessibility of K-ionomer is detected up to 169 °C.

Domains of Pyrococcus furiosus L-asparaginase fold sequentially and assemble through strong intersubunit associative forces.

Here, we report the folding and assembly of a Pyrococcus furiosus-derived protein, L-asparaginase (PfA). PfA functions as a homodimer, with each monomer made of distinct N- and C-terminal domains. The purified individual domains as well as single Trp mutant of each domain were subjected to chemical denaturation/renaturation and probed by combination of spectroscopic, chromatographic, quenching and scattering techniques. We found that the N-domain acts like a folding scaffold and assists the folding of remaining polypeptide. The domains displayed sequential folding with the N-domain having higher thermodynamic stability. We report that the extreme thermal stability of PfA is due to the presence of high intersubunit associative forces supported by extensive H-bonding and ionic interactions network. Our results proved that folding cooperativity in a thermophilic, multisubunit protein is dictated by concomitant folding and association of constituent domains directly into a native quaternary structure. This report gives an account of the factors responsible for folding and stability of a therapeutically and industrially important protein.

Time-dependent mechanical properties of tough ionic-covalent hybrid hydrogels

Hybrid gels featuring interpenetrating covalent and ionic crosslinked networks have recently been shown to exhibit both high toughness and recoverability of strain-induced network damage. The high toughness results from the energy dissipated as entropically strained network strands are released by the dissociation of ionic crosslinks. As in the so-called double network hydrogels, the toughening process is inherently linked to network damage. This damage, however, can be recovered to a large degree in hybrid gels due to the reformation of ionic associations when the gel is unloaded. The stability of the ionic network under load is here investigated and it is shown that these networks show large stress relaxation at constant strain, time dependent stress-strain behaviour and rate-dependent toughness. A double exponential model is invoked to mathematically describe the stress relaxation of the hybrid gels indicating at least two relaxation mechanisms. The rate-dependent toughness and the relaxation behaviour of the hybrid gels are attributed to the labile unzipping of the ionic crosslinks which is assumed to be load and time dependent.

Thermal stability of ionic nets with CuII ions coordinated to di-2-pyridyl ketone: Reversible crystal-to-crystal phase transformation

Supramolecular networks are crystalline materials based on connections between metal ions through organic ligands. In this sense, the combination of polycarboxylate anions and dipyridyl ligands is an effective strategy to produce extended structures. However, sometimes the 3D arrangement results in an ionic network, and this is the case for the novel compounds [Cu((py)2C(OH)2)2](H2bta) (1) and [Cu((py)2C(OH)2)2](fum) (2) where (py)2C(OH)2 is the gem-diol of di-2-pyridyl ketone ((py)2CO), H2bta2− is the divalent anion of 1,2,4,5-benzenetetracarboxylic acid (H4bta), and fum2− is the divalent anion of fumaric acid (butenedioic acid). Both compounds were synthesized and structurally characterized by means of single crystal X-ray diffraction and IR spectroscopy. The thermal behavior of both compounds was analyzed through TG/DTA and TDX, concluding that the thermal stability is influenced by the dehydration of the coordinated molecules and counter-anions. Additionally, 13C NMR measurements were performed to analyze the reversible crystal-to-crystal phase transformation observed for 1.

Structural and catalytic effects of proline substitution and surface loop deletion in the extended active site of human carbonic anhydrase II.

Bioengineering of a thermophilic enzyme starting from a mesophilic scaffold has proven to be a significant challenge, as several stabilizing elements have been proposed to be the foundation of thermal stability, including disulfide bridges, surface loop reduction, ionic pair networks, proline substitutions and aromatic clusters. This study emphasizes the effect of increasing the rigidity of human carbonic anhydraseII (HCAII; EC 4.2.1.1) via incorporation of proline residues at positions 170 and 234, which are located in surface loops that are able to accommodate restrictive main-chain conformations without rearrangement of the surrounding peptide backbone. Additionally, the effect of the compactness of HCAII was examined by deletion of a surface loop (residues 230-240) that had been previously identified as a possible source of thermal stability for the hyperthermophilic carbonic anhydrase isolated from the bacterium Sulfurihydrogenibiumyellowstonense YO3AOP1. Differential scanning calorimetry analysis of these HCAII variants revealed that these structural modifications had a minimum effect on the thermal stability of the enzyme, while kinetic studies showed unexpected effects on the catalytic efficiency and proton transfer rates. X-ray crystallographic analysis of these HCAII variants showed that the electrostatic potential and configuration of the highly acidic loop (residues 230-240) play an important role in its high catalytic activity. Based on these observations and previous studies, a picture is emerging of the various components within the general structural architecture of HCAII that are key to stability. These elements may provide blueprints for rational thermal stability engineering of other enzymes. Structural data have been submitted to the Protein Data Bank under accession numbers 4QK1 (K170P), 4QK2 (E234P) and 4QK3 (Δ230-240).

Ionic conductivity enhancement of polymer electrolytes with ceramic nanowire fillers.

Solid-state electrolytes provide substantial improvements to safety and electrochemical stability in lithium-ion batteries when compared with conventional liquid electrolytes, which makes them a promising alternative technology for next-generation high-energy batteries. Currently, the low mobility of lithium ions in solid electrolytes limits their practical application. The ongoing research over the past few decades on dispersing of ceramic nanoparticles into polymer matrix has been proved effective to enhance ionic conductivity although it is challenging to form the efficiency networks of ionic conduction with nanoparticles. In this work, we first report that ceramic nanowire fillers can facilitate formation of such ionic conduction networks in polymer-based solid electrolyte to enhance its ionic conductivity by three orders of magnitude. Polyacrylonitrile-LiClO4 incorporated with 15 wt % Li0.33La0.557TiO3 nanowire composite electrolyte exhibits an unprecedented ionic conductivity of 2.4 × 10(-4) S cm(-1) at room temperature, which is attributed to the fast ion transport on the surfaces of ceramic nanowires acting as conductive network in the polymer matrix. In addition, the ceramic-nanowire filled composite polymer electrolyte shows an enlarged electrochemical stability window in comparison to the one without fillers. The discovery in the present work paves the way for the design of solid ion electrolytes with superior performance.

Construction of a lithium ion transport network in cathode with lithiated bis(benzene sulfonyl)imide based single ion polymer ionomers

We demonstrate a novel method to construct a lithium ion transport network in cathode materials by replacing PVDF with lithiated poly(bis(4-carbonyl benzene sulfonyl)imide-co-bis(4-amino benzene sulfonyl)imide) as the binder. The single ion conducting polymer was synthesized via polycondensation of bis(4-carbonyl benzene sulfonyl)imide and bis(4-amino benzene sulfonyl)imide followed by lithium ion exchange. By blending the ionomers with LiFePO4 and acetylene carbon, the ionic network was well constructed, resulting in a maximum use of active cathode material inside the cathode. The membrane of the polymer electrolyte exhibits an ionic conductivity of 0.14 mS cm−1 at room temperature, a high ion transference number of 0.92 and a wide electrochemical window of 4.5 V (vs. Li+/Li). A lithium ion battery assembled with the single ion conducting polymer electrolyte delivers excellent performance at room temperature with various C-rates.

Ionic conductivity and molecular dynamic behavior in supramolecular ionic networks; the effect of lithium salt addition

Supramolecular ionic networks combine singular properties such as self-healing behaviour and ionic conductivity. In this work we present an insight into the ionic conductivity and molecular dynamic behaviour of an amorphous and semicrystalline supramolecular ionic networks (iNets) that were synthesised by self-assembly of difunctional imidazolium dicationic molecules coupled with (trifluoromethane-sulfonyl) imide dianionic molecules. Relatively low ionic conductivity values were obtained for the semicrystalline iNet below its melting point (Tm=101°C) in comparison with the amorphous iNet for which the conductivity significantly increased (∼3 orders of magnitude) above 100°C. Upon LiTFSI doping, the semicrystalline iNet reached conductivity values ∼ 10−3Scm−1 due to enhanced mobility of the network which was supported by solid-state static NMR. Furthermore, the overlapping of 19F and 7Li resonance lines from both the semicrystalline network and the LiTFSI suggests fast molecular motions.

Nanoporous ionic organic networks: stabilizing and supporting gold nanoparticles for catalysis.

Nanoporous ionic organic networks (PIONs) with a high ionic density (three cation-anion pairs per unit) have been synthesized by a facile SN2 nucleophilic substitution reaction. Owing to the electrostatic and steric effect, those ionic networks with porous channels can stabilize and support gold (Au) nanoparticles (NPs) in 1-2 nm. The Au@PION hybrid materials used as a heterogeneous catalyst were highly active, selective, and stable in the aerobic oxidation of saturated alcohols.

Structure and Dynamics of Coarse-Grained Ionomer Melts in an External Electric Field

We perform molecular dynamics simulations on a set of ionomer melts in the presence of a static, external electric field. We employ the same coarse-grained bead–spring model from our previous simulations, which characterized the zero-field morphologies and dynamics of the isolated or percolated ionic aggregates observed in these systems. Here we investigate the electric field effects on these aggregates. In the linear response regime, the morphology of both isolated and percolated aggregates is unaltered because the force between the two ions at contact is much stronger than the force on an ion due to the external field. However, the same fields are strong enough to bias the local ion dynamics so that ions in the percolated systems, which contain a continuous ionic network, transition to the steady state drift regime. Furthermore, the field biases the motion of oppositely charged ions in opposite directions and decorrelates the ionic aggregates along the field direction. In the systems with isolated ionic...

Ionic Liquid Solvated Polymer Networks for Stretchable Electronics

Electronic skin and textiles are two current applications of stretchable electronics that require compliant solid electrolytes. Ionic liquid solvated polymer networks that are both tough and elastic to high strains are ideal electrolytes for stretchable electronics. Robust ionogels eshibiting elasticity as large as 480% strain, breaking strength as high as 3.2 MPa and tear energy as high as 2.8 kJ m−2 were produced. These ionogels are within their glass-to-rubber transition at 20°C and are categorized as plasticisized polymer networks. At 20°C and 105 Hz the ionogels are a polymer glass that inhibits ionic conductivity.

Polyamino acid display on cell surfaces enhances salt and alcohol tolerance of Escherichia coli.

Microbes employ cell membranes for reducing exogenous stresses. Polyamino acid display on microbial cell surfaces and their effects on microbial chemical stress tolerance were examined. Growth analysis revealed that displays of polyarginine, polyaspartate and polytryptophan substantially enhanced tolerance of Escherichia coli to NaCl. A titration assay indicated that polyarginine and polyaspartate altered cell surface charges, implying tolerance enhancement via ion atmosphere and/or ionic bond network formations for electrostatic ion repulsion. The enhancement by polytryptophan may have arisen from surface hydrophobicity increase for hydrophobic ion exclusion, because of a strong correlation between hydrophobic characters of amino acids and their effects on tolerance enhancement. The display also enhanced tolerance to other salts and/or alcohols in E. coli and to NaCl in Saccharomyces cerevisiae. Thus polyamino acid display has the potential as an approach for conferring chemical stress tolerance on various microbes.

Structural Insights into the Nature of the Unique Anion Binding Site within the Cardiac Ryanodine Receptor N-Terminal Region and Associated Disease Mutations

Ryanodine receptors (RyRs) are large intracellular calcium-release channels of the endo/sarcoplasmic reticulum that play a critical role in mediating excitation-contraction coupling. Mutations within the skeletal muscle isoform (RyR1) are associated with the pharmacogenetic disorder known as Malignant Hyperthermia (MH) as well as congenital myopathies. Concurrently, mutations within the cardiac (RyR2) isoform have been linked to life-threatening arrhythmias, such as catecholaminergic polymorphic ventricular tachycardia (CPVT), a potential precursor of sudden cardiac death. While recent high-resolution structures have provided some mechanistic insights as to how mutations may impact receptor function, this subject requires more work. The RyR1 amino-terminal region contains an elaborate ionic interaction network embedded between its three domains which is key to the protein's stability. Despite all the ionic interaction partners being conserved within RyR2, the replacement of two histidine residues with Tyr125 and Arg420 within RyR2 is enough to abolish the ionic network and introduce a unique central anion binding site within RyR2. Here, we present structural insights into the nature of the RyR2 anion binding site. A 2.6A crystal structure has been solved of the amino-terminal RyR2 region (residues 1-547) into which two histidines, Y125H and R420H, were introduced which abolished chloride binding but which failed to restore the ionic network of its counterpart in RyR1. The amino-terminal intrasubunit domain-domain interfaces of both RyR1 and RyR2 are each targeted by over twenty disease-associated mutations. Here, we provide the biochemical and structural characterization of a novel MH RyR1 mutation, H113Q, and a potential CPVT-causing mutant, RyR2 R420W, both of which reside at a domain-domain interface.

Two-Dimensional FTIR as a Tool to Study the Chemical Interactions within Cellulose-Ionic Liquid Solutions

In this study two-dimensional FTIR analysis was applied to understand the temperature effects on processing cellulose solutions in imidazolium-based ionic liquids. Analysis of the imidazolium ionνC2–H peak revealed hydrogen bonding within cellulose solutions to be dynamic on heating and cooling. The extent of hydrogen bonding was stronger on heating, consistent with greater ion mobility at higher temperature when the ionic liquid network structure is broken. At ambient temperatures a blue shiftedνC2–H peak was indicative of greater cation-anion interactions, consistent with the ionic liquid network structure. Both cellulose and water further impact the extent of hydrogen bonding in these solutions. The FTIR spectral changes appeared gradual with temperature and contrast shear induced rheology changes which were observed on heating above 70°C and cooling below 40°C. The influence of cellulose on solution viscosity was not distinguished on initial heating as the ionic liquid network structure dominates rheology behaviour. On cooling, the quantity of cellulose has a greater influence on solution rheology. Outcomes suggest processing cellulose in ionic liquids above 40°C and to reduce the impacts of cation-anion effects and enhance solubilisation, processing should be done at 70°C.

Ionic semi-interpenetrating networks as a new approach for highly conductive and stretchable polymer materials

The synthesis and characterization of ionically conductive polymer films with high stretchability and good elasticity based on ionic semi-interpenetrating polymer networks (semi-IPNs) are discussed.

Cholesteric liquid crystals with an electrically controllable reflection bandwidth based on ionic polymer networks and chiral ions

The reflection bandwidth can be tuned dynamically by electric fields in the visible wavelength regime.

Low-velocity super-lubrication of sodium-alginate/polyacrylamide ionic-covalent hybrid double-network hydrogels.

Structural and frictional behaviours of sodium alginate (SA)/polyacrylamide (PAAm) ionic-covalent hybrid, sequential double-network (DN) hydrogels against glass have been investigated in water, NaCl and CaCl2 aqueous solutions using a rotational rheometer. Dilution of adsorptive elastohydrodynamic friction for the PAAm covalent network with repulsive hydrodynamic lubrication for the minor SA ionic network was found to control the frictional stresses of the SA/PAAm gels within between those of the SA and PAAm single-network gels. A tentative qualitative model was proposed to describe the impact of ionic environmental solution on the frictional behaviour of the hybrid gel by selectively affecting the SA-network structure and friction. It was revealed that strong Debye shielding in the NaCl solution significantly reduced the thickness of the electric double layer for hydrodynamic lubrication of the SA network, which made the SA/PAAm gel's friction the highest among the three solutions. Dramatically increased ionic cross-linking of the SA network in the CaCl2 solution, although effectively mediated by the PAAm-network flexible skeleton, still functioned partially to conserve a portion of the SA fractional boundary-friction at the interface, making the friction of the hybrid gel intermediate among the three solutions. In contrast, extreme hydration of the SA network in water sharply increased the volume fraction of its unshielded hydrodynamic lubrication at the interface, which greatly reduced the SA/PAAm's friction to the lowest among the three solutions. We have thus incorporated for the first time both super-lubrication (frictional coefficients of below 10(-2) over low sliding-velocities of 3 × 10(-5) to 2 × 10(-3) m s(-1)) and previously reported high fracture energy (over 9000 J m(-2)) into a single ionic-covalent hybrid DN hydrogel, which is the SA/PAAm (∼1/8.5 w/w) gel in water. Effects of inversion of DN-formation sequence further indicated that frictional behaviours (i.e. frictional stress-sliding velocity profiles) of the hybrid sequential DN hydrogels (SA/PAAm and PAAm/SA), respectively, were primarily determined by those of the second networks (PAAm and SA), presumably due to the formation of first-second network "core-shell" structures at the blob scale. Frictional stress of the SA/PAAm gel was increased monotonically with external normal pressure at all of the sliding velocities investigated in the three solutions, which was in agreement with the predictions from the repulsion-adsorption model proposed by Gong et al.

Supramolecular ionic networks with superior thermal and transport properties based on novel delocalized di-anionic compounds

Supramolecular ionic networks based on delocalized di-anionic compounds combined ionic conductivity and self-healing properties into the same material.

Elaboration of hybrid cotton fibers treated with an ionogel/carbon nanotube mixture using a sol-gel approach

Abstract Ionic liquid (IL) synergy with other materials may influence their properties significantly. Nevertheless, their advantageous liquid state turns out to be an impediment for applications in devices which need stable solid state shaping. In the current study we present a novel method where new siloxane functionalized IL acts as a modifier for carbon nanotubes (CNTs) and titanium alkoxide-CNT coated hybrid cotton fibers. This elaborated route carried out by interconnected and entangled ionic liquid, sol-gel and solid carbon nanotube networks opens up opportunities for functionalization of sol-gel materials with different shapes and sizes. The comparison of properties of IL, ionogel, ionogel/CNT mixture and titanium alkoxide coatings is performed. Ionogel-modified cotton fibers have increased hydrophobicity, linear density, breaking force and ultimate strength as compared to the uncoated cotton fibers. These properties are ensured even after washing threads with water. A uniformly coated CNT network around the fibers strengthens the material and increases its electric conductivity. New type of hybrids can be utilized in formulations which have UV-shielding and hydrophobic properties as well as for antibacterial properties. Characterization studies of the product were carried out by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), optical microscopy and infrared (IR) spectroscopy.