Changes In Ionic Conductivity Research Articles

Gadolinium-Sensitive Artificial Nanochannel Membrane for Information Encryption.

Inspired from ion channels in the myelinated axon of Xenopus laevis found to be affected by gadolinium on axonal currents, we present a solid nanochannel membrane sensitive to gadolinium (Gd3+), which can be achieved via the use of the macrocyclic triacetic acid derivative in the host-guest chemistry approach. The macrocyclic nanochannel has good responsiveness toward Gd3+, even at the nanomolar concentration level, evidenced by discernible changes in rectification, ionic conductance, and XPS analyses. Notably, the Gd3+-sensitive nanochannel membrane can be switched by the addition of a diethylenetriaminepentaacetic acid (DTPA) derivative. Further studies have indicated that the gated behavior of Gd3+ in the nanochannel can be attributed to the strong binding strength between DO3A and Gd3+, which induces a surface charge reversal within the nanochannel. The mechanism has been confirmed through several experimental techniques, including isothermal titration calorimetry (ITC) experiments, fluorescence titration experiments, and finite element analysis. Based on its Gd3+ responsiveness of the constructed ion channel, we successfully developed an advanced multilevel information encryption application of the artificial solid nanochannel membrane. Furthermore, it is anticipated that a more effective encryption system will be built by utilizing the bionic ion channel system's ease of use and straightforward functionalization.

Fast Responsive and Highly Sensitive Ethanol Gas Sensors Designed by Agar‐Laponite Hybrid Hydrogels

AbstractLaponite, a synthetic nanosilicate clay and agar, a natural polysaccharide, both imbibe large amount of water and form into hydrogels. Various physical and chemical stimuli elicit the hydrogel response, which has been applied in designing diverse sensors and biomedical systems. In this work, we exploit the change in hydrogel's ionic conductivity due to volatile organic compounds (VOCs) (e. g. ethanol) interaction with the surfaces of Laponite‐Agar hybrid hydrogel films. Gas sensing studies are carried out on silicon (Si) and flexible polyethylene terephthalate (PET) substrates by monitoring the resistance changes. Pristine Laponite hydrogel has shown increase in resistance as it interacted with the ethanol, whereas pure agar and Laponite‐Agar have shown decrease in resistance. Moreover, Laponite‐Agar gel films have exhibited high sensitivity, fast response (4 s) and recovery time (15 s) with lowest detection limit of 6 ppm. Selectivity test carried shows high ethanol sensing response and exhibited very good reproducibility. Observed responses and sensing mechanism are discussed based on changes in ionic conduction resulted due to interacting ethanol with the gel surface network structure. Present study paves the way for understanding and designing low cost, soft and flexible hydrogel gas sensors.

(Invited) Zwitter Ion-Promoted Hybrid Sepiolite Membranes for Energy Applications

Functionalized natural clays exhibit significant potential as electrode materials, solid-state electrolytes and separators in energy storage and conversion devices. Features that evoke interest in clay minerals are their (1) porous structures and adsorption properties, (2) tunable surface areas, (3) remarkable thermal and mechanical stabilities, (4) abundant natural reserves, and (5) cost. By tweaking such features along with functionalization with desired molecules, they can be used as an ideal candidate for solid-state electrolyte and battery separators. Naturally occurring clays possess layered silicate structures with interchangeable, intercalated ions and tunable chemical properties. Among them, sepiolite, which is a hydrated magnesium silicate, is one of the most appealing clays having a high-aspect ratio. The blocks and channels in sepiolite with discontinuity in the external silica sheet expose a significant number of surface-silanol groups directly accessible to functionalize with organic and inorganic species. Moreover, its exceptionally high surface area and high cation exchange capacity (CEC) compared to other clays enables easy functionalization, thereby imparting exceptional mechanical durability and material properties that can be used for myriads of applications.In this work a sustainable, cost-effective, environmentally benign, carbon-neutral, and bio-friendly sepiolite clay composites have been developed using betaine and ionic liquid without the use of polymers, metals, or carbon-based precursors.Betaine-modified sepiolite clay composites have been synthesized to fabricate flexible and mechanically robust membranes. These membranes are characterized using powder X-ray diffraction, ATR-FTIR, XPS, surface area analyses, rheology, and imaging techniques (e.g., SEM). Morphological analyses reveal sepiolite possesses needle-shaped morphology in a highly aggregated state. The addition of betaine disaggregates such bundles, forming a 3D network with unique “clay anemone” structures. The XRD patterns are consistent with the literature reflecting no change in the d-spacing and corresponding 2θ value (d100 2θ = 7.4 ͦ) before and after betaine treatment. This provides strong evidence of modification limited to the external surface. ATR-FTIR spectra of the sepiolite-betaine composite membranes show the presence of 935, 1330,1391, and 1616 cm-1 frequencies that correspond to C-N-C, N-C-H, C-N and C=Ostretching respectively. This suggests the successful functionalization of sepiolite clay by betaine through an intercalation mechanism. Further, the electrochemical properties of betaine-modified sepiolite membranes are investigated by electrochemical impedance spectroscopy (EIS) measurements to study the ion dynamics of the hybrid membranes. The room temperature ionic conductivities of these membranes are measured using lithium perchlorate (LiClO4) in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvent (1:1). The concentration of LiClO4 is varied to monitor the change in ionic conductivity and ease of ion transfer through the membranes. The highest ionic conductivity is observed in 0.1M LiClO4 concentration which is superior to the ionic conductivity of sepiolite or hybrid materials with carbon-based precursors, metal ions, quantum dots, or polymers. Viscoelastic properties of the sepiolite slurries with varying concentrations of betaine are also studied to investigate the interaction mechanism between the sepiolite-betaine system and correlate the impact of these interactions on the structure and ionic conductivity of the hybrid sepiolite membranes. Contrary, the IL-sepiolite membranes exhibit superior ionic conductivity compared to betaine-sepiolite membranes, which gives a distinct advantage in the physicochemical and electrochemical properties. The composites are synthesized with varying concentrations of ionic liquid-to-clay ratios and pressed into pellets for conductivity measurements. The highest ionic conductivity of 1 x 10-2 S/cm is achieved by modifying the clay with 10 wt. % IL specimens. This helps to improve the ionic conductivity of the IL-clays. The XRD spectra of sepiolite-IL composites show almost no change in the 2 theta values and peak intensities compared to the pristine sepiolite, confirming the crystalline structure of the sepiolite clay is intact after functionalization with IL. The ATR-FTIR confirms the IL-sepiolite modification with the appearance of a new band at 1345 cm-1 that is attributed to -CH stretching frequencyfrom the alkyl chains of IL present in the clay structures.We have developed a new approach using earth-abundant silicate-based materials to synthesize hybrid zwitterion-modified sepiolite clay membranes. Such materials are not only flexible and mechanically durable, but they also exhibit enhanced ionic conductivity and show exceptional thermal and chemical durability at temperatures above 300 °C and with most aggressive organic solvents, making them a superior candidate for an ergonomic and eco-friendly membrane-based separator for energy devices and gas absorption. Current work is in progress to understand the fundamentals underlying the unique structure-property relationship of hybrid sepiolite, zwitterion-silicate interactions, and conductivity variance with sepiolite architectures, thereby exploiting newer and better properties for application in catalysis, flexible electronics, and biomedical fields. Figure 1

Impact of Mechanical Stimuli on PEO-Litfsi Stiffness and Ionic Conductivity

Recently a large emphasis has been placed on developing safer electrolytes for lithium-ion batteries as a response to an increase in battery demand. Solid polymer electrolytes, such as those based on polyethylene oxide (PEO) show good resistance to mechanical loading, and when coupled with ceramic fillers demonstrate enhance ionic conductivity as well. Prior to this work, efforts have been made to determine the effects mechanical stimuli have on the stiffness and ionic conductivity of the electrolyte.1–3 However, while previous research has primarily focused on bulk EIS measurements of the electrolyte, here we leverage atomic force microscopy (AFM) to modulate the tip-substrate contact force from a few piconewtons to tens of millinewtons to study the correlation between mechanical loading and ionic conductivity, along with measuring the evolution of the substrate stiffness as a function of mechanical cycling.In this study, we contact the PEO-LiTFSI surface with an electrically conductive Pt-coated tip and mechanically cycle the sample by applying a pre-determined contact force a set number of times. By keeping the contact force and time constant, we extracted the cycle-dependent evolution of the sample stiffness. Results show that stiffness is reduced 30% within the first ten cycles, and then minimally changes with subsequent cycling, matching the results from bulk measurements. Changes in ionic conductivity as a function of mechanical cycling are then measured using electrical characterization techniques. To gain a better understanding of how conductivity and stiffness are evolving, we conducted a parametric study by varying tip size, contact force, and number of mechanical cycles. From early results, we found that electrical resistance increases by ~3% (from 2985 Ohm to 3075 Ohm) after 100 cycles of mechanical force ranging between ~ 0 nN to 450 nN with a 5 µm radius tip. The change in the electrical resistance is believed to originate from the local amorphization of PEO-LiTFSI induced by the mechanical stimuli and resulting change of the local conductivity. These results can be leveraged to further understand how mechanical stimuli affects the mechanical and electrical characteristics of solid electrolytes and help establish a model to predict long-term stability and performance of batteries.This work was supported by the National Science Foundation (#2125640).(1) Yoon, D. et al., ACS Appl. Energy Mater, 6 (18), 9400, 2023(2) Li, X. et al., ACS Appl. Mater. Interfaces, 11 (25), 22745, 2019(3) Liu, L. et al., Nano Energy, 69, 104398, 2020

The Influence of Calendering Process on the Graphite Anode

Calendering, or pressing, is the final property-defining process for battery electrode manufacturing to maximize the volumetric capacity of the cell through the compaction of an electrode between two large calender rollers12. On one hand, it can reduce the porosity of battery materials thus increase the conductivity of the materials. On the other hand, it can control the thickness of the electrodes, making sure it is uniform and proper thickness to guarantee the minimal variation in the cell thickness, reaching even stack pressure for module assembly and impacting the thermal management [3]. The calendering process significantly influence the performance of lithium-ion battery (LIB).Graphite anode coating on Cu foil was chosen as our baseline coating for this calendering process investigation. The slurry was mixed in a planetary and dispersive mixer and then coated using reverse comma coating method by a scale-up coater with drying zones of 70 °C. Then the coating was calendered by a calendering machine at various conditions.Calendering, though seemingly a simply process, is influenced by several different parameters significantly. In this study, we systematically investigated the calendering process by carrying-out a Design-of-experiment (DOE). The following calendering parameters were investigated: the parameters of calendering machine gap size, calendering pressure, and the speed of the coating web. The calendered graphite coating was then measured for the morphology by scanning electron microscopy (SEM), the pore size change by BET surface area measurement, and Direct current internal resistance (DCIR) by building half cells and cycling and Electrochemical Impedance Spectroscopy (EIS) at 50% State-of-Charge (SOC).The result showed that pressure is the most critical parameter for calendering and the internal resistance and ionic conductivity changes in response to the calendering parameters. The half-cell with calendering at the pressure of 37 MPa, gap size targeted for 30% porosity, the BET surface area around 0.75 m2/g showed highest cell capacity and lowest internal resistance.

Controlling Ionic Conductivity in Organometallic Ionic Liquids through Light-Induced Coordination Polymer Formation and Thermal Reversion.

Owing to their high ionic conductivity and negligible vapor pressure, ionic liquids (ILs) find applications in various electronic devices. However, fabricating IL-based photocontrollable devices remains a challenge. In this study, we developed organometallic ILs with reversible light- and heat-controlled ionic conductivities for potential use in tunable devices. The physical properties and stimulus responses of ILs containing a cationic sandwich Ru complex with two coordinating substituents were investigated. UV photoirradiation of these ILs triggered cation photodissociation, resulting in their transformation into viscoelastic coordination polymers wherein the coordinating substituents bridged the Ru centers. Owing to the anion coordination, salts with coordinating anions such as CF3SO2NCN-, B(CN)4-, and BF2(CN)2- exhibited faster response and higher conversion than those with noncoordinating anions including (FSO2)2N- and (CF3SO2)2N-. All photoproducts reverted to their original ILs upon heating, except for the photoproduct of the BF2(CN)2 salt, which decomposed upon heating. Light- and heat-induced reversible changes occur in most cases between the high-ionic-conductive IL state and low-ionic-conductive coordination polymer state. Unlike previously reported ILs with three or one cation substituent, the current ILs exhibited both high reactivity and large ionic conductivity changes.

Concentration effects on dynamic fluctuations in structure and thermodynamic properties of LiCl–AlCl3 molten Salt: Insights from ab initio molecular dynamics

The short–range and mid–range structural features, as well as thermodynamic properties of a LiCl–AlCl3 mixed molten salt at 873 K, were investigated as a function of AlCl3 concentration using ab initio molecular dynamics methods. In all solutions, the short-range structure of Al3+ reveals a regular tetrahedral [AlCl4]– unit. These tetrahedral units exist in isolation within dilute AlCl3 solution and polymerize into dimers or trimers through Al–Cl–Al bridge bonds in concentrated solutions. The dynamic dissociation analysis of Al3+ and Li+ structures indicates that the Al–Cl bond considerably stronger than Li–Cl bond. The polymerization of the [AlCl4]– units leads to the dissociation of the Li+ coordination shells into freely isolated cations. Furthermore, we examined changes in density, self-diffusion coefficient, and ionic conductivity with varying AlCl3 concentration in terms of thermodynamic properties. The conductivity and self-diffusion coefficient of Li+ showed a noticeable peak at 50 % concentration. This peak may be associated with the aggregation of [AlCl4]– units and the dissociation of Li+ coordination shells.

Solid-state synthesis and ion transport characteristics of the β-KSbF4 for all-solid-state fluoride-ion batteries

All-solid-state fluoride ion batteries (FIBs) have been recently considered as a post-lithium-ion battery system due to their high safety and high energy density. Just like all solid-state lithium batteries, the key to the development of FIBs lies in room-temperature electrolytes with high ionic conductivity. β-KSbF4 is a kind of promising solid-state electrolyte for FIBs owing to its rational ionic conductivity and relatively wide electrochemical stability window at room temperature. However, the previous synthesis routes of β-KSbF4 required the use of highly toxic hydrofluoric acid and the ionic conductivity of as-prepared product needs to be further improved. Herein, the β-KSbF4 sample with an ionic conductivity of 1.04 × 10−4 S cm−1 (30 °C) is synthesized through the simple solid-state route. In order to account for the high ionic conductivity of the as-synthesized β-KSbF4, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) are used to characterize the physicochemical properties. The results show that the as-synthesized β-KSbF4 exhibits higher carrier concentration of 1.0 × 10−6 S cm−1 Hz−1 K and hopping frequency of 1.31 × 106 Hz at 30 °C due to the formation of the fluorine vacancies. Meanwhile, the hopping frequency shows the same trend as the changes of ionic conductivity with the changes of temperature, while the carrier concentration is found to be almost constant. The two different trends indicate the hopping frequency is mainly responsible for the ionic conduction behavior within β-KSbF4. Furthermore, the all-solid-state FIBs, in which Ag and Pb + PbF2 are adopted as cathode and anode, and β-KSbF4 as fluoride ion conductor, are capable of reversible charge and discharge. The assembled FIBs show a discharge capacity of 108.4 mA h g−1 at 1st cycle and 74.2 mA h g−1 at 50th cycle. Based on an examination of the capacity decay mechanism, it has been found that deterioration of the electrolyte/electrode interface is an important reason for hindering the commercial application of FIBs. Hence, the in-depth comprehension of the ion transport characteristics in β-KSbF4 and the interpretation of the capacity fading mechanism will be conducive to promoting development of high-performance FIBs.

The influence of defects on conduction processes in chalcogenide semiconductor compounds

Due to the strong dependence on the intrinsic defectiveness of structures, semiconductor compounds based on metal chalcogenides have a wide spread in kinetic properties and high growth temperatures of materials, as well as a tendency to self-compensation of defects. It has been shown that an increase in defectivity in the cation sublattice leads to a decrease in ionic conductivity in copper chalcogenides, and an increase in temperature leads to an increase in ionic conductivity due to a change in mobility. The low activation energy indicates a strong intrinsic disorder of the cation part of the lattice. In copper chalcogenides, the presence of hopping conductivity at small deviations from stoichiometry is explained by compensation and a high concentration of vacancies. Under such conditions, this activation energy is the activation energy for the movement of copper ions throughout the crystal and almost all metal ions contribute to the ionic electrical conductivity. In semiconductor compounds based on metal chalcogenides with deviations from stoichiometry, the activation energy of cationic conductivity does not change, since the defects that arise in this case do not introduce large changes in ionic conductivity with temperature. The increase in ionic conductivity with increasing temperature is due to a change in mobility, since the carrier concentration remains unchanged. The latter is determined only by the structural features of the phases. Deviation from stoichiometry in compounds makes it necessary to take into account the movement of the main charge carriers in the allowed zones, and the movement of carriers along vacancies. The properties of metal chalcogenides are largely determined by the characteristics of their preparation and depend on the relative ratio of metal and chalcogen atoms, as well as the presence of intrinsic defects and their influence on the mechanism of behavior of charge carriers and transfer phenomena.

In Situ/Operando Techniques for Unraveling Mechanisms of Ionic Transport in Solid-State Lithium Indium Halide Electrolyte

Over the past years, lithium-ion solid-state batteries have demonstrated significant advancements regarding such properties as safety, long-term endurance, and energy density. Solid-state electrolytes based on lithium halides offer new opportunities due to their unique features such as a broad electrochemical stability window, high lithium-ion conductivity, and elasticity at close to melting point temperatures that could enhance lithium-ion transport at interfaces. A comparative study of lithium indium halide (Li3InCl6) electrolytes synthesized through a mechano-thermal method with varying optimization parameters revealed a significant effect of temperature and pressure on lithium-ion transport. An analysis of Electrochemical Impedance Spectroscopy (EIS) data within the temperature range of 25–100 °C revealed that the optimized Li3InCl6 electrolyte reveals high ionic conductivity, reaching 1.0 mS cm−1 at room temperature. Herein, we present the utilization of in situ/operando X-ray Photoelectron Spectroscopy (XPS) and in situ X-ray powder diffraction (XRD) to investigate the temperature-dependent behavior of the Li3InCl6 electrolyte. Confirmed by these methods, significant changes in the Li3InCl6 ionic conductivity at 70 °C were observed due to phase transformation. The observed behavior provides critical information for practical applications of the Li3InCl6 solid-state electrolyte in a broad temperature range, contributing to the enhancement of lithium-ion solid-state batteries through their improved morphology, chemical interactions, and structural integrity.

Synthesis, Thermodynamic Properties, and Ionic Conductivity of Compounds Based on Bismuth Niobates Doped by Rare-Earth Elements (A Review)

Synthesis methods, thermodynamic and functional properties of compounds based on bismuth niobates doped with rare-earth elements (REEs) are presented. These compounds are promising materials for fuel cells, ceramic oxygen generators, electrocatalysis, etc. As show the data generalized, most compounds have a cubic structure of the δ-form of bismuth oxide, which has the highest ionic conductivity among solid-state ionic conductors. The compounds have high lattice enthalpy and are therefore promising high-energy compounds. The review summarizes studies on the basic thermodynamic characteristics of bismuth niobates doped with rare earth elements. The change in standard enthalpies of formation, lattice enthalpies, and heat capacity when replacing one rare earth element with another is analyzed. It is shown that as the radius of rare earth elements decreases, the standard enthalpies of formation increases and lattice enthalpies increases. The change in ionic conductivity with changes in temperature and rare earth element content has been studied. It has been shown that with increasing temperature and REE content, conductivity increases.

Designing dynamic metal-coordinated hydrophobically associated mechanically robust and stretchable hydrogels for versatile, multifunctional applications in strain sensing, actuation and flexible supercapacitors

Combining the synergistic effect of dynamic metal–ligand cross-linking and hydrophobic association along with low density chemical cross-linking, we have developed a mechanically robust and stretchable hydrogel that was synthesized by micellar copolymerization of acrylamide (AM), maleic acid (MA) and butyl acrylate monomer. With optimized composition, this hydrogel showed ∼ 3 MPa tensile strength & ∼ 60 MPa compressive strength. The hydrogel is stretchable ∼ 7 times of its original length. These hydrogel materials are flexible and can be folded, bent, and twisted due to their high toughness (∼10 MJ m−3) and low elastic modulus (0.56 MPa). Because of the dynamic nature of metal–ligand interaction and hydrophobic association, the hydrogel showed high energy dissipation under tensile deformation and quick recovery of the dissipated energy after repeated loading and unloading. This hydrogel showed pH responsive mechanical properties. At lower pH, the mechanical strength and elastic modulus of the hydrogel deteriorated due to the dissociation of metal–ligand interaction. This concept was further used for demonstrating shape memory effect in these materials. Utilizing the colorimetric change in presence of Fe3+ and H+, the hydrogel can be used for data encryption-decryption technology. Combining with a thermoresponsive hydrogel (Poly (N-Isopropyl acrylamide)) layer, our hydrogel showed excellent thermoresponsive reversible actuation effect. Furthermore, because of its high ionic conductivity and strain dependent resistance change, the hydrogel can be used as a flexible strain sensor and as a compressible electrolyte in flexible supercapacitor devices.

Tailoring electrolytes for Sn-based anodes toward Li storage at a low temperature of -50°C

High-capacity storage in Li-ion batteries with graphite anodes remains a challenge at low temperature. By contrast, metal-based composite anode materials, including Sn metal, have shown good lithium storage capabilities at low temperature. However, the suitable low temperature electrolyte is still infancy to achieve high efficiency capacity of Sn-based anode in ultra-low temperature. Herein, a 2-methytetrahydrofuran (2Me-THF)-based low temperature electrolyte is proven to support the excellent lithium capability of Sn-based anode at ultra-low temperatures. The formulated 2Me-THF electrolyte exhibited small changes in viscosity and ionic conductivity with decreasing temperature. A SnO2-LiF-G (graphite) electrode with 1 M lithium bis(trifluoromethanesulfonyl)imide-(2Me-THF) electrolyte maintained 80% of the room temperature reversible capacity at -30°C and delivered a reversible capacity of 650 mAh g−1, even at -50°C, under a current density of 100 mA g−1. Furthermore, a detailed characterization based on Fourier Transform Infrared Spectroscopy, X-ray Photoelectron Spectroscopy and Time-of-flight Secondary ion Mass Spectrometry confirmed that the formed inorganic-rich solid electrolyte interphase on the electrode surface effectively maintained the solid-liquid interfacial stability at low temperature. This work provided design concepts for ultralow temperature electrolytes for metal-based anodes, which were especially helpful for further promoting batteries for low temperature applications.

Softening of PEO-LiTFSI/LLZTO Composite Polymer Electrolytes for Solid-State Batteries under Cyclic Compression.

Composite polymer electrolytes (CPEs) strike an effective balance between ionic conductivity and mechanical flexibility for lithium-ion solid-state batteries. Long-term performance, however, is limited by capacity fading after hundreds of charge and discharge cycles. The causes of performance degradation include multiple contributing factors such as dendrite formation, physicochemical changes in electrolytes, and structural remodeling of porous electrodes. Among the many factors that contribute to performance degradation, the effect of stress specifically on the composite electrolyte is not well understood. This study examines the mechanical changes in a poly(ethylene oxide) electrolyte with bis(trifluoromethane) sulfonimide. Two different sizes of Li6.4La3Zr1.4Ta0.6O12 particles (500 nm and 5 μm) are compared to evaluate the effect of the surface-to-volume ratio of the ion-conducting fillers within the composite. Cyclic compression was applied to mimic stress cycling in the electrolyte, which would be caused by asymmetric volume changes that occur during charging and discharging cycles. The electrolytes exhibited fatigue softening, whereby the compressive modulus gradually decreased with an increase in the number of cycles. When the electrolyte was tested for 500 cycles at 30% compressive strain, the compressive modulus of the electrolyte was reduced to approximately 80% of the modulus before cycling. While the extent of softening was similar regardless of particle size, CPEs with 500 nm particles exhibited a significant reduction in ionic conductivity after cyclic compression (1.4 × 10-7 ± 2.3 × 10-8 vs 1.1 × 10-7 ± 2.0 × 10-8 S/cm, mean ± standard deviation, n = 4), whereas there was no significant change in ionic conductivity for CPEs with 5 μm particles. These observations -performed deliberately in the absence of charge-discharge cycles -show that repetitive mechanical stresses can play a significant role in altering the performance of CPEs, thereby revealing another possible mechanism for performance degradation in all-solid-state batteries.

Biomimetic Ion Channel Regulation for Temperature-Pressure Decoupled Tactile Perception.

The perception of temperature and pressure of skin plays a vital role in joint movement, hand grasp, emotional expression, and self-protection of human. Among many biomimetic materials, ionic gels are uniquely suited to simulate the function of skin due to its ionic transport mechanism. However, both the temperature and pressure sensing are heavily dependent on the changes in ionic conductivity, making it impossible to decouple the temperature and pressure signals. Here, a pressure-insensitive and temperature-modulated ion channel is designed by synergistic strategies for gel skeleton's compact packing and ultra-thin structure, mimicking the function of the temperature ion channel in human skin. This ion-confined gel can completely suppress the pressure response of the temperature sensing layer. Furthermore, a temperature-pressure decoupled ionic sensor is fabricated and it is demonstrated that the ionic sensor can sense complex signals of temperature and pressure. This novel and effective approach has great potential to overcome one of the current barriers in developing ionic skin and extending its applications.

Understanding the Effect of Trace Solvent Content on Properties of Polymer Electrolytes through Molecular Dynamics Simulations

The rapid growth of mobile, portable, wearable and flexible electronics leads to the increasing demand for energy storage devices using solid-state polymer electrolytes (PEs), which outperform liquid electrolytes in terms of safety, mechanical properties, and simplicity of device fabrication and packaging. However, processing PEs will always introduce solvent molecules that greatly affect the ionic conductivity and mechanical properties. For example, PEs prepared through solution-casting methods always have solvent residues. A trace amount of water molecules absorbed from the air is also inevitable. Recently, we demonstrated the controlled introduction of solvent molecules to PEs to balance the ionic conductivity and mechanical stiffness for structural energy storage applications. To better understand how solvent molecules behave and interact with other components in PEs, here we present the molecular dynamics simulation of a representative polymer electrolyte system with various water content. We use simulation results to determine the effect of trace water content before forming a liquid phase on ionic conductivity and mechanical properties. The insights into the molecular interactions in the PE system will help us design and optimize Pes’ composition and processing for practical applications.The simulation model of polymer electrolyte is built with polyethylene oxide (PEO) and lithium perchlorate (LiClO4) with various water contents, in which the water molecule to lithium-ion ratio ranges from 0 to 3. The electrolyte with each water content is simulated between two graphene electrodes to determine its ionic conductivity. Uniaxial deformation has been performed on the electrolyte to obtain the mechanical properties. All simulations were performed using the molecular dynamics simulation code LAMMPS with the CHARMM force field.The results show that the ionic conductivity of the polymer electrolyte system increases significantly (up to one order of magnitude) with the increase of water content (up to 3 water molecules per lithium ion), even when the added water does not form a continuous liquid phase. The change of ionic conductivity with water content is correlated to the degree of association between different types of ions or molecules in the system, as evidenced by the evaluation of the radial distribution functions. As the association between polymer molecules and lithium ions reduces with increasing water, it becomes easier for the lithium ions to diffuse and resulting in higher ionic conductivity. It is also observed that the perchlorate ions’ interactions with polymer molecules remain the same with different water contents, which shows different roles of lithium ions and perchlorate ions in ion conduction in this system. On the other hand, the modulus of elasticity of the polymer electrolyte does not change much with the increase of water, which agrees with the previous experimental work of our group. This means that the trace amount of water is strongly associated with other solid molecules or ions and is not affecting the stiffness of the system as long as no liquid phase is formed. The results will lead to novel strategies to design polymer electrolytes with both high ionic conductivity and good mechanical properties for flexible or multifunctional energy storage applications.

Thinking about the action potential: the nerve signal as a window to the physical principles guiding neuronal excitability.

Ever since the work of Edgar Adrian, the neuronal action potential has been considered as an electric signal, modeled and interpreted using concepts and theories lent from electronic engineering. Accordingly, the electric action potential, as the prime manifestation of neuronal excitability, serving processing and reliable "long distance" communication of the information contained in the signal, was defined as a non-linear, self-propagating, regenerative, wave of electrical activity that travels along the surface of nerve cells. Thus, in the ground-breaking theory and mathematical model of Hodgkin and Huxley (HH), linking Nernst's treatment of the electrochemistry of semi-permeable membranes to the physical laws of electricity and Kelvin's cable theory, the electrical characteristics of the action potential are presented as the result of the depolarization-induced, voltage- and time-dependent opening and closure of ion channels in the membrane allowing the passive flow of charge, particularly in the form of Na+ and K+ -ions, into and out of the neuronal cytoplasm along the respective electrochemical ion gradient. In the model, which treats the membrane as a capacitor and ion channels as resistors, these changes in ionic conductance across the membrane cause a sudden and transient alteration of the transmembrane potential, i.e., the action potential, which is then carried forward and spreads over long(er) distances by means of both active and passive conduction dependent on local current flow by diffusion of Na+ ion in the neuronal cytoplasm. However, although highly successful in predicting and explaining many of the electric characteristics of the action potential, the HH model, nevertheless cannot accommodate the various non-electrical physical manifestations (mechanical, thermal and optical changes) that accompany action potential propagation, and for which there is ample experimental evidence. As such, the electrical conception of neuronal excitability appears to be incomplete and alternatives, aiming to improve, extend or even replace it, have been sought for. Commonly misunderstood as to their basic premises and the physical principles they are built on, and mistakenly perceived as a threat to the generally acknowledged explanatory power of the "classical" HH framework, these attempts to present a more complete picture of neuronal physiology, have met with fierce opposition from mainstream neuroscience and, as a consequence, currently remain underdeveloped and insufficiently tested. Here we present our perspective that this may be an unfortunate state of affairs as these different biophysics-informed approaches to incorporate also non-electrical signs of the action potential into the modeling and explanation of the nerve signal, in our view, are well suited to foster a new, more complete and better integrated understanding of the (multi)physical nature of neuronal excitability and signal transport and, hence, of neuronal function. In doing so, we will emphasize attempts to derive the different physical manifestations of the action potential from one common, macroscopic thermodynamics-based, framework treating the multiphysics of the nerve signal as the inevitable result of the collective material, i.e., physico-chemical, properties of the lipid bilayer neuronal membrane (in particular, the axolemma) and/or the so-called ectoplasm or membrane skeleton consisting of cytoskeletal protein polymers, in particular, actin fibrils. Potential consequences for our view of action potential physiology and role in neuronal function are identified and discussed.

Structural relaxation dynamics of a silicate glass probed by refractive index and ionic conductivity

AbstractRelaxation occurs spontaneously in all glasses and is a fundamental step of important technological processes, such as annealing, crystal nucleation, and chemical strengthening by ion exchange. Despite extensive studies over the past decades, there are still conflicting results on whether the kinetics of structural relaxation depends on the analyzed property. Thus, in this study, we used a lithium disilicate glass as a model composition to determine the structural relaxation kinetics during physical aging experiments by measuring the time evolution of the refractive index and ionic conductivity down to 35 K below the initial fictive temperature. In all cases, variations in these properties were adequate to capture the structural changes throughout the aging experiments. At each temperature, the experimental relaxation data fit quite well with the classical stretched exponential relation. We also found that the relaxation process starts faster when probed by ionic conductivity than by refractive index; however, they show similar average relaxation times. These very small structural rearrangements are always the same, but ionic conductivity changes faster than refractive index at the beginning of the process. Our comprehensive results strongly indicate that relaxation dynamics is indeed dependent on the analyzed property.

Monte Carlo simulation and experimental validation of plant microtubules cathode in biodegradable battery

For the first time, electrochemical methods are utilized to study the response of tubulin monomers (extracted from plant source such as Green Peas: Arachis Hypogea) towards charge perturbations in the form of conductivity, conformational changes via self-assembly and adsorption on Au surface. The obtained dimerization and surface adsorption energetics of the tubulins from Cyclic Voltammetry agree well with the literature value of 6.9 and 14.9 kCal/mol for lateral and longitudinal bond formation energy respectively. In addition to the effects of charge perturbations on change in structure, ionic and electronic conductivity of tubulin with increasing load are investigated and found to be 1.25 Sm−1 and 2.89 mSm−1 respectively. The electronic conductivity is 1.93 times higher than the literature value of 1.5 mSm−1, demonstrating the fact that the microtubules (dimer of tubulins, MTs) from plant source can be used as a semiconductor electrode material in energy conversion and storage applications. Thus, motivated by the Monte Carlo simulation and electrochemical results the MTs extracted from plant source are used as cathode material for energy storage device such as Bio-battery and the Galvanostatic Charge/Discharge studies are carried out in coin cell configuration. The configuration of the bio-battery cell is as follows: Al/CB//PP-1M KCl//MTs/SS; where SS and Al are used as current collectors for cathode and anode respectively, Polypropylene (PP) membrane soaked in 1M KCl as electrolyte and Carbon Black (CB) is the anode material. Another configuration of the cell would be replacement of CB by biopolymer such as ethyl cellulose anode (Al/EC/PP-1M KCl/MTs/SS).

Ionic Conduction and Dielectric Response of Nanoparticle-Coupled Hydrogel Network Polymer Electrolytes

The molecular level understanding of ion and polymer dynamics in nanoparticle-coupled hydrogel network polymer electrolytes is investigated by linear dielectric and viscoelastic measurements covering broad ranges of frequency and temperature. We prepare hydrogel polymer electrolytes (HPEs), composed of Li+ conducting hydrophilic poly(lithium acrylate) (PLiA) as the HPE matrix and vinyl-functionalized silica nanoparticles (NPs) as cross-linking points, via radical polymerization and sol–gel reaction. The NP content variation leads to changes in ionic conductivity (σDC), dielectric constant (εs), relaxation frequency, and elastic modulus, which are important characteristic factors for understanding ion transport. From the physical model of electrode polarization (EP), allowing for the determination of the number density of simultaneously conducting ions and their mobility, the NP-containing HPEs (HPE-NP) have simultaneously higher conducting ion concentration (p) and mobility (μ), resulting in higher ionic conductivity (σDC ∼ pμ), compared to the HPE without NPs. The temperature dependence of p and μ follows Arrhenius (thermally activated) and Vogel–Fulcher (segmentally driven) temperature dependences, respectively. In addition to the lower frequency EP, the HPEs show higher frequency relaxation (α2), attributed to ions rearranging. NP incorporation leads to faster α2 relaxation and higher static dielectric constant εs (shorter Bjerrum length lB). Time–temperature superposition (tTS) works well for these electrolytes and is applied to construct master curves of viscoelasticity and in-phase conductivity. In the end, the NP-containing HPE-based supercapacitor is fabricated using carbon nanotube yarn (CNTY) electrodes and shows stable electrochemical performance, demonstrating that our HPE can be a solid-state polymer electrolyte for energy storage devices.