Ion-polymer Interactions Research Articles

Sodium iodide dopant mediated enhancements in energy storage characteristics of polysaccharide polymer electrolytes

Sodium iodide dopant influencing the properties of polysaccharide polymer sodium carboxymethyl cellulose is analyzed in this work by FTIR, XRD, DSC, TGA, SEM, UTM, and electrical. Solvation of I− and Na+ ions by the −OH group has disrupted the intra– and intermolecular hydrogen bonds between the polymers escorting to a decrease in crystallinity and creating a pathway for ion diffusion. The formation of transient crosslink and the physical environment created by the polymer-ion interaction have affected the rigidity of the polymer chains as well as the thermal stability of the NaCMC−NaI system. I− ion influences the ESW of the NaCMC−NaI system by forming various iodine species. Trapping of the I− ion for the NaCMC70−NaI30 sample has resulted in a drop in ionic conductivity manifested in the transient ionic current curve. A cation transference number of 0.14 indicates the dominance of anion in the ion conduction mechanism. An energy density of 720 mWhkg−1 and power density of 60 mWkg−1 was achieved for a dry cell incorporated with a CI25 sample as the electrolyte and separator.

Molecular dynamics simulations of the effect of starch on transport of water and ions through graphene nanopores.

We use molecular dynamics simulations to unravel the molecular level mechanisms underlying the structure and dynamics of water and ions flowing through nanoporous starch-graphene membranes. Our findings indicate that there is a significant tendency for the formation of short-range order in close proximity to the graphene membrane surface. This leads to a greater concentration of water and ions, suggesting strong interactions between the membrane and the saltwater solution. Furthermore, we found that the starch-graphene membrane was most efficient in sieving out ions when the starch loading is 15 wt.%, and the pore diameter is 14Å. At these conditions, the starch-graphene membrane showed a high water transport rate and maintained a high level of ion rejection. We investigated the effect of loading of starch and the pore diameter on the pressure-induced transport, structure, and dynamics of Na+, Cl-, and water using the GROMACS 2021.4 package. We further analyze the density profiles of water and ions in the context of ion-polymer and water-polymer interactions and provide mechanistic insights into the piston-induced flow of saltwater through the starch-graphene membranes using Visual Molecular Dynamics (VMD) software.

Design of High-Entropy Tape Electrolytes for Compression-Free Solid-State Batteries.

Advanced solid electrolytes with strong adhesion to other components are the key for the successes of solid-state batteries. Unfortunately, traditional solid electrolytes have to work under high compression to maintain the contact inside owing to their poor adhesion. Here, a concept of high-entropy tape electrolyte (HETE) is proposed to simultaneously achieve tape-like adhesion, liquid-like ion conduction, and separator-like mechanical properties. This HETE is designed with adhesive skin layer on both sides and robust skeleton layer in the middle. The significant properties of the three layers are enabled by high-entropy microstructures which are realized by harnessing polymer-ion interactions. As a result, the HETE shows high ionic conductivity (3.50 ± 0.53 × 10-4 S cm-1 at room temperature), good mechanical properties (toughness 11.28 ± 1.12MJ m-3, strength 8.18 ± 0.28MPa), and importantly, tape-like adhesion (interfacial toughness 231.6 ± 9.6 J m-2). Moreover, a compression-free solid-state tape battery is finally demonstrated by adhesion-based assembling, which shows good interfacial and electrochemical stability even under harsh mechanical conditions, such as twisting and bending. The concept of HETE and compression-free solid-state tape batteries may bring promising solutions and inspiration to conquer the interface challenges in solid-state batteries and their manufacturing.

Microphase-Separated Elastic and Ultrastretchable Ionogel for Reliable Ionic Skin with Multimodal Sensation.

Bioinspired artificial skins integrated with reliable human-machine interfaces and stretchable electronic systems have attracted considerable attention. However, the current design faces difficulties in simultaneously achieving satisfactory skin-like mechanical compliance and self-powered multimodal sensing. Here, this work reports a microphase-separated bicontinuous ionogel which possesses skin-like mechanical properties and mimics the multimodal sensing ability of biological skin by ion-driven stimuli-electricity conversion. The ionogel exhibits excellent elasticity and ionic conductivity, high toughness, and ultrastretchability, as well as a Young's modulus similar to that of human skin. Leveraging the ion-polymer interactions enabled selective ion transport, the ionogel can output pulsing or continuous electrical signals in response to diverse stimuli such as strain, touch pressure, and temperature sensitively, demonstrating a unique self-powered multimodal sensing. Furthermore, the ionogel-based I-skin can concurrently sense different stimuli and decouple the variations of the stimuli from the voltage signals with the assistance of a machine-learning model. The ease of fabrication, wide tunability, self-powered multimodal sensing, and the excellent environmental tolerance of the ionogels demonstrate a new strategy in the development of next-generation soft smart mechano-transduction devices.

Role of Dielectric Drag in Circumventing the Solubility-Diffusivity Trade-off in Zwitterionic Copolymer Membranes.

Recent experiments have revealed that random zwitterionic amphiphilic copolymer (r-ZAC) membranes exhibit excellent Cl-/F- permselectivity circumventing the solubility-diffusivity trade-off. We conducted molecular dynamics simulations to investigate the origin of the experimental results on the transport of sodium halides in r-ZAC membranes. Our results indicate that the enhancement of Cl-/F- diffusivity selectivity in r-ZAC membranes (relative to that in bulk water) stems from the increase in dielectric drag dominating over the increase in Stokes drag, zwitterionic group-induced steric hindrance, and ion-polymer interactions. The importance of dielectric drag is further demonstrated by showing that reduction in ionic charges leads to a complete reversal of the diffusivity selectivity trends. We conclude that leveraging the impact of hydrophilic nanoconfinement on the dynamics of water can be utilized as a strategy to simultaneously augment solubility selectivity and diffusivity selectivity for separations, wherein the flux of the larger ionic species is desired over that of the smaller.

Unraveling Polymer–Ion Interactions in Electrochromic Polymers for their Implementation in Organic Electrochemical Synaptic Devices

AbstractOwing to low‐power, fast and highly adaptive operability, as well as scalability, electrochemical random‐access memory (ECRAM) technology is one of the most promising approaches for neuromorphic computing based on artificial neural networks. Despite recent advances, practical implementation of ECRAMs remains challenging due to several limitations including high write noise, asymmetric weight updates, and insufficient dynamic ranges. Here, inspired by similarities in structural and functional requirements between electrochromic devices and ECRAMs, high‐performance, single‐transistor and neuromorphic devices based on electrochromic polymers (ECPs) are demonstrated. To effectively translate electrochromism into electrochemical ion memory in polymers, this study systematically investigates polymer–ion interactions, redox activity, mixed ionic–electronic conduction, and stability of ECPs both experimentally and computationally using select electrolytes. The best‐performing ECP‐electrolyte combination is then implemented into an ECRAM device to further explore synaptic plasticity behaviors. The resulting ECRAM exhibits high linearity and symmetric conductance modulation, high dynamic range (≈1 mS or ≈6x), and high training accuracy (>84% within five training cycles on a standard image recognition dataset), comparable to existing state‐of‐the‐art ECRAMs. This study offers a promising approach to discover and design novel polymer materials for organic ECRAMs and demonstrates potential applications, taking advantage of mature knowledge basis on electrochromic materials and devices.

Cation–polymer interactions and local heterogeneity determine the relative order of alkali cation diffusion coefficients in PEGDA hydrogels

Current research efforts are focused on endowing polymer membranes with ion–ion selectivity by incorporating ion–polymer interactions into materials to bias the selective partitioning and or diffusivity of one species over another. However, little is known about the impact of such interactions on the mechanisms of ion transport. In this study, we probe the influence of cation–polymer interactions on cation, anion, and salt diffusivity in a model membrane material, poly(ethylene glycol) diacrylate (PEGDA) by modeling concentrated polyethylene oxide solutions via molecular dynamics simulations. These results are compared to published experimental data for LiCl, NaCl, and KCl diffusion in PEGDA. Experimentally, the order of salt and cation diffusion coefficients for LiCl, NaCl, and KCl deviate from the order in aqueous solutions. Simulations identify these deviations to arise from cation–polymer coordination in the membrane. Both the fraction of bound cations and the average binding lifetime increases with decreasing cation hydration free energy (moving down the alkali series), leading to different diffusivity trends in the membrane compared to solution. However, to recover the experimentally observed order of diffusivities cations and salt in our simulations, we needed to incorporate membrane heterogeneity explicitly via a polymer charge scaling procedure. Together, our results indicate that cation–polymer interactions, as well as spatial heterogeneity within the membrane, play a critical role in dictating the observed order of alkali cation and salt diffusion coefficients in membranes.

Giant Negative Thermopower Enabled by Bidirectionally Anchored Cations in Multifunctional Polymers.

The lack of high-quality ionic thermoelectric materials with negative thermopowers has stimulated scientists' broad research interest. The effective adjustment of the interaction between ions and a polymer network is an important way to achieve high-quality ion thermoelectric properties. Integrating different types of ion-polymer interactions into the same thermoelectric device seems to lead to unexpected gains. In this work, we propose a strategy for bidirectionally anchoring cations to synergistically generate a giant negative thermopower and high ionic conductivity. This is mainly achieved through synergistic ion-polymer coordination and Coulomb interactions. An ionic thermoelectric material was prepared by infiltrating a polycation electrolyte [poly(diallyldimethylammonium chloride)] with CuCl2 into the poly(vinyl alcohol)-chitosan aerogel. The confinement effect of copper-coordinated chitosan on cations, the repulsive property of the polycationic electrolyte on cations, and the unique chemical configuration of a transition metal chloride anion ([CuCl4]2-) are the fundamental guarantees for achieving a thermopower of -28.4 mV·K-1. Moreover, benefiting from the high charge density of the polycationic electrolyte, we obtain an ionic conductivity of 40.5 mS·cm-1. These findings show the application prospect of synergistic different types of ion-polymer interactions in designing multifunctional ionic thermoelectric materials.

Anion Effects on the Liquid-Liquid Equilibrium Behavior of Pluronic L64 + Water + Sodium Salts at Different pH: Determination of Thermodynamic Parameters

Two-phase aqueous systems have replaced and simplified steps in extraction and purification processes, especially for biocompounds. Thus, this study evaluated the liquid-liquid equilibrium behavior of Pluronic L64 + water + sodium salts at pH 5.0, 7.5, and 10.0. Sodium sulfate demonstrated the greatest phase separation, followed by sodium citrate and sodium tartrate. Higher pH values resulted in larger biphasic regions. The polymer distribution coefficients increased with the addition of salt. As pH increased, there was a tendency for Pluronic L64 to migrate to the polymer-rich phase. The Gibbs energy of micellization between −11,000 and −25,000 kJ mol−1 indicated the spontaneity of the process micellization for all systems, showing lower values for the systems with sodium sulfate. This parameter was related to the anion speciation at each pH. Besides, the effects of water structuring around ions and ion-polymer interaction influenced the phase separation.

A guide for the characterization of organic electrochemical transistors and channel materials.

The organic electrochemical transistor (OECT) is one of the most versatile devices within the bioelectronics toolbox, with its compatibility with aqueous media and the ability to transduce and amplify ionic and biological signals into an electronic output. The OECT operation relies on the mixed (ionic and electronic charge) conduction properties of the material in its channel. With the increased popularity of OECTs in bioelectronics applications and to benchmark mixed conduction properties of channel materials, the characterization methods have broadened somewhat heterogeneously. We intend this review to be a guide for the characterization methods of the OECT and the channel materials used. Our review is composed of two main sections. First, we review techniques to fabricate the OECT, introduce different form factors and configurations, and describe the device operation principle. We then discuss the OECT performance figures of merit and detail the experimental procedures to obtain these characteristics. In the second section, we shed light on the characterization of mixed transport properties of channel materials and describe how to assess films' interactions with aqueous electrolytes. In particular, we introduce experimental methods to monitor ion motion and diffusion, charge carrier mobility, and water uptake in the films. We also discuss a few theoretical models describing ion-polymer interactions. We hope that the guidelines we bring together in this review will help researchers perform a more comprehensive and consistent comparison of new materials and device designs, and they will be used to identify advances and opportunities to improve the device performance, progressing the field of organic bioelectronics.

From Hofmeister to hydrotrope: Effect of anion hydrocarbon chain length on a polymer brush

HypothesisSpecific ion effects govern myriad biological phenomena, including protein–ligand interactions and enzyme activity. Despite recent advances, detailed understanding of the role of ion hydrophobicity in specific ion effects, and the intersection with hydrotropic effects, remains elusive. Short chain fatty acid sodium salts are simple amphiphiles which play an integral role in our gastrointestinal health. We hypothesise that increasing a fatty acid’s hydrophobicity will manifest stronger salting-out behaviour. ExperimentsHere we study the effect of these amphiphiles on an exemplar thermoresponsive polymer brush system, conserving the carboxylate anion identity while varying anion hydrophobicity via the carbon chain length. Ellipsometry and quartz crystal microbalance with dissipation monitoring were used to characterise the thermoresponse and viscoelasticity of the brush, respectively, whilst neutron reflectometry was used to reveal the internal structure of the brush. Diffusion-ordered nuclear magnetic resonance spectroscopy and computational investigations provide insight into polymer-ion interactions. FindingsSurface sensitive techniques unveiled a non-monotonic trend in salting-out ability with increasing anion hydrophobicity, revealing the bundle-like morphology of the ion-collapsed system. An intersection between ion-specific and hydrotropic effects was observed both experimentally and computationally; trending from good anti-hydrotrope towards hydrotropic behaviour with increasing anion hydrophobicity, accompanying a change in hydrophobic hydration.

Characterizing Ion-Polymer Interactions in Aqueous Environment with Electric Fields.

Polymers make the basis of highly tunable materials that could be designed and optimized for metal recovery from aqueous environments. While experimental studies show that this approach has potential, it suffers from a limited knowledge of the detailed molecular interaction between polymers and target metal ions. Here, we propose to calculate intrinsic electric fields from polarizable force field molecular dynamics simulations to characterize the driving force behind Eu3+ motion in the presence of poly(ethylenimine methylenephosphonate), a specifically designed metal chelating polymer. Focusing on the metal chelation initiation step (i.e., before binding), we can rationalize the role of each molecule on ion dynamics by projecting these electric fields along the direction of ion motion. We find that the polymer functional groups act indirectly, and the polymer-metal ion interaction is actually mediated by water. This result is consistent with the experimental observation that metal sequestration by these polymers is entropically driven. This study suggests that electric field calculations can help the design of metal chelating polymers, for example, by seeking to optimize polymer-solvent interactions rather than polymer-ion interactions.

Characterizing Ion-Polymer Interactions in Aqueous Environment with Electric Fields

Characterizing Ion-Polymer Interactions in Aqueous Environment with Electric Fields

Decoupling Ion Transport and Matrix Dynamics to Make High Performance Solid Polymer Electrolytes.

Transport of ions through solid polymeric electrolytes (SPEs) involves a complicated interplay of ion solvation, ion-ion interactions, ion-polymer interactions, and free volume. Nonetheless, prevailing viewpoints on the subject promote a significantly simplified picture, likening ion transport in a polymer to that in an unstructured fluid at low solute concentrations. Although this idealized liquid transport model has been successful in guiding the design of homogeneous electrolytes, structured electrolytes provide a promising alternate route to achieve high ionic conductivity and selectivity. In this perspective, we begin by describing the physical origins of the idealized liquid transport mechanism and then proceed to examine known cases of decoupling between the matrix dynamics and ionic transport in SPEs. Specifically we discuss conditions for "decoupled" mobility that include a highly polar electrolyte environment, a percolated path of free volume elements (either through structured or unstructured channels), high ion concentrations, and labile ion-electrolyte interactions. Finally, we proceed to reflect on the potential of these mechanisms to promote multivalent ion conductivity and the need for research into the interfacial properties of solid polymer electrolytes as well as their performance at elevated potentials.

Influence of pH, salt ions, and binary mixtures of different molecular weights on the extensional rheology of polyethylene oxide

In the context of modifying the extensional rheology of agricultural sprays to improve retention of sprays on plants, here we characterize the extensional rheology of dilute solutions of polyethylene oxide (PEO). Specifically, we examine the influence of pH and ionic strength, which vary significantly among agricultural sprays, as well as binary mixtures of two different nominal molecular weights of the polymer additive. Because PEO is nonionic, common intuition would predict that varying the pH and/or adding salt ions would have a minimal or negligible effect. However, the results presented here show a significant, complex, nonmonotonic, and ion-specific trend that is systematically documented for the first time. The role of shear degradation when mixing the polymer solutions is ruled out, and the data suggest that specific ion-polymer interactions appear to be more likely than changes in the solvent quality for producing this unexpected trend. We discuss some possible mechanistic explanations for the trend and highlight the potential impacts on product formulation as well as the need for improved theory of polymer physics.

Structure–Property Relationships for Polyether-Based Electrolytes in the High-Dielectric-Constant Regime

Establishing general structure–property relationships for polymer electrolytes is crucial to enable design of improved materials to advance solid-state energy storage. We report the relationship between dielectric constant, glass transition temperature, and ionic conductivity for polyether-based electrolytes with dielectric constants of the polyether host within the range 7–35 at 60 °C. The ionic conductivities of the polyether and lithium bis(trifluoromethylsulfonyl)imide mixtures ranged from 10–7 to 10–3 S/cm. In this higher-dielectric-constant regime, here defined as a polymer with a dielectric constant greater than that of poly(ethylene oxide) (ca. 9.0), the glass transition temperature increased with dielectric constant while ionic conductivity decreased. These results complement a recent report on the low-dielectric-constant regime, where the ionic conductivity was limited by the dielectric constant and ion dissociation. In the high-dielectric-constant regime explored here, segmental dynamics are slowed due to stronger polymer–polymer and polymer–ion interactions, resulting in decreased ionic conductivity and associated increase in neat polymer glass transition temperature. The disparate chemical structures of the polymers of this study, along with the results of past coarse-grained molecular dynamics simulations, support the generality of these conclusions and speak to the difficulty of identifying a single molecular characteristic leading to the design of high-conductivity polymer electrolytes. Widely used poly(ethylene oxide) represents a near-optimal balance between the low- and high-dielectric-constant regimes. To improve upon the ionic conductivity limitations of polymer electrolytes, single-component polymer hosts are unlikely to resolve the trade-off between the need for ion dissociation while retaining rapid segmental dynamics.

Polymer-ion interactions in PVDF@ionic liquid polymer electrolytes: A combined experimental and computational study

Polymer electrolytes based on poly (vinylidene fluoride) (PVDF) with different concentrations (40, 55, 65, and 75 wt.%) of 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][FSI] were investigated by experimental and molecular dynamics (MD) simulation techniques. The addition of ionic liquid (IL) slightly decreases the electrochemical stability window, as estimated by linear scanning voltammetry. For the neat PVDF, the simulated glass transition temperature (Tg) was obtained at 233.1 K, which is in good agreement with experimental data. Higher contents of IL promoted an increase of the glass transition temperature of the system, indicating a reduction of the polymer segmental mobility, possibly due to the increase of the interactions with the ions. Ionic conductivities were obtained through experimental measurements and MD simulations, which were calculated by Nernst-Einstein and Einstein-Helfand methods. The MD simulation results reproduced the general trend of the experimental ionic conductivities for the GPEs. The studied GPEs systems present an ionic conductivity that obeys a linear Arrhenius behavior, confirming that the ionic mobility is not dependent on the polymer motion.

Polymer-Ion Interactions in a Pvdf@Ionic Liquid Polymer Electrolytes: A Combined Experimental and Computational Study

Polymer-Ion Interactions in a Pvdf@Ionic Liquid Polymer Electrolytes: A Combined Experimental and Computational Study

Correlations between Composition, Matrix Dynamics and Ca2+ Conductivity in Ca-Polyoxyethylene Polymer Electrolytes

In the last decades, the humankind is facing a radical transition towards the development of sustainable methods for the energy conversion endowed with a lower environmental impact with respect to fossil fuels. Examples are solar, wind, tides, etc., which, unfortunately, suffer from an intermittent availability and a misalignment between disposability and demand, thus requesting the coupling with energy storage devices. In addition to this, the growing market of electric vehicles is requesting more performing and lower cost batteries with respect to those based on the lithium-ion technology. In this regard, the development of novel chemistries, preferentially based on multivalent metals, is an open quest. Among the different multivalent metals, calcium can be considered a good choice, as it shows a similar theoretical volumetric capacity and reduction potential with respect to lithium (i.e., 2.06 vs. 2.06 Ah cm-3 and -3.05 vs. -2.87 V against SHE for Li and Ca, respectively) and a high abundance in the Earth’s crust [1]. The widespread of calcium batteries is mainly bottlenecked by the development of suitable Ca2+ ion-conducting materials able to deposit and strip calcium metal [1-4]. Moreover, the understanding of the coordination and exchange of Ca2+ ions in the electrolyte, and thus the conductivity mechanism, is mostly unknown, especially when a polymer matrix is used.In this work we investigate the conductivity mechanism of Ca2+-ion in polyoxyethylene (POE) solid polymer electrolytes (SPEs) for calcium secondary batteries by means of broadband electrical spectroscopy studies. Three different calcium salts are taken under consideration (i.e., CaTf2, Ca(TFSI)2 and CaI2) in order to demonstrate the role of the anion in the formation of ion-polymer host matrix interactions, and thus in the modulation of the conductivity mechanism. It is shown that the long-range charge migration processes occurring along the different percolation pathways of these systems are generally coupled with the polymer host matrix dynamics and are influenced by the temperature and the anion nature. Indeed, it is demonstrated that the anions are able to induce the formation of “dynamic crosslinks”, whose density is regulated by their different steric hindrance and charge density. Concluding, this study paves the way towards the understanding of Ca2+ conduction in POE-based electrolytes. Acknowledgements This work has been supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 829145 (FETOPEN-VIDICAT). V. Di Noto thanks the University Carlos III of Madrid for the “Catedras de Excelencia UC3M-Santander” (Chair of Excellence UC3M-Santander).

Relationship between Ionic Conductivity, Glass Transition Temperature, and Dielectric Constant in Poly(vinyl ether) Lithium Electrolytes.

We report a partial elucidation of the relationship between polymer polarity and ionic conductivity in polymer electrolyte mixtures comprising a homologous series of nine poly(vinyl ether)s (PVEs) and lithium bis(trifluoromethylsulfonyl)imide. Recent simulation studies have suggested that low dielectric polymer hosts with glass transition temperatures far below ambient conditions are expected to have ionic conductivity limited by salt solubility and dissociation. In contrast, high dielectric hosts are expected to have the potential for high ion solubility but slow segmental dynamics due to strong polymer-polymer and polymer-ion interactions. We report results for PVEs in the low polarity regime with dielectric constants of about 1.3 to 9.0. Ionic conductivity measured for the PVE and salt mixtures ranged from about 10-10 to 10-3 S/cm. In agreement with the predictions from computer simulations, the ionic conductivity increased with dielectric constant and plateaued as the dielectric approached 9.0, comparable to the dielectric constant of the widely used poly(ethylene oxide).