Internal catalysis significantly promotes the bond exchange of covalent adaptable polyurethane networks.

Self-healing covalent adaptable networks (CANs) are not only of fundamental interest but also of practical importance for achieving carbon neutrality and sustainable development. However, there is a trade-off between the mobility and cross-linking structure of CANs, making it challenging to develop CANs with excellent mechanical properties and high self-healing efficiency. Here, we report the utilization of a highly dynamic four-arm cross-linking unit with an internally catalyzed oxime-urethane group to obtain CAN-based ionogel with both high self-healing efficiency (>92.1%) at room temperature and superior mechanical properties (tensile strength 4.55 MPa and toughness 13.49 MJ m-3). This work demonstrates the significant potential of utilizing the synergistic electronic, spatial, and topological effects as a design strategy for developing high-performance materials.

Highly Ionic Conductive, Stretchable, and Tough Ionogel for Flexible Solid-State Supercapacitor.

The increasing demand for wearable electronics calls for advanced energy storage solutions that integrate high  electrochemical performances and mechanical robustness. Ionogel is a promising candidate due to its stretchability combined with high ionic conductivity. However, simultaneously optimizing both the electrochemical and mechanical performance of ionogels remains a challenge. This paper reports a tough and highly ion-conductive ionogel through ion impregnation and solvent exchange. The fabricated ionogel consists of double interpenetrating networks of long polymer chains that provide high stretchability. The polymer chains are crosslinked by hydrogen bonds that induce large energy dissipation for enhanced toughness. The resultant ionogel possesses mechanical stretchability of 26, tensile strength of 1.34 MPa, and fracture toughness of 4175 J m-2. Meanwhile, due to the high ion concentrations and ion mobility in the gel, a high ionic conductivity of 3.18 S m-1 at room temperature is achieved. A supercapacitor of this ionogel sandwiched with porous fiber electrodes provides remarkable areal capacitance (615 mF cm-2 at 1 mA cm-2), energy density (341.7 µWh cm-2 at 1 mA cm-2), and power density (20 mW cm-2 at 10 mA cm-2), offering significant advantages in applications where high efficiency, compact size, and rapid energy delivery are crucial, such as flexible and wearable electronics.

3D Printing of Thermo-Mechano-Responsive Photoluminescent Noncovalent Cross-Linked Ionogels with High-Stretchability and Ultralow-Hysteresis for Wearable Ionotronics and Anti-Counterfeiting.

Ionogel has recently emerged as a promising ionotronic material due to its good ionic conductivity and flexibility. However, low stretchability and significant hysteresis under long-term loading limit their mechanical stability and repeatability. Developing ultralow hysteresis ionogels with high stretchability is of great significance. Here, a simple and effective strategy is developed to fabricate highly stretchable and ultralow-hysteresis noncovalent cross-linked ionogels based on phase separation by 3D printing of 2-hydroxypropyl acrylate (HPA) in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4). Ingeniously, the sea-island structure of the physically cross-linked network constructed by the smaller nanodomains and larger nanodomain clusters significantly minimizes the energy dissipation, endowing these ionogels with remarkable stretchability (>1000%), ultra-low hysteresis (as low as 0.2%), excellent temperature tolerance (-33-317 °C), extraordinary ionic conductivity (up to 1.7 mS cm-1), and outstanding durability (5000 cycles). Moreover, due to the formation of nanophase separation and cross-linking structure, the as-prepared ionogels exhibit unique thermochromic and multiple photoluminescent properties, which can synergistically be applied for anti-counterfeiting and encrypting. Importantly, flexible thermo-mechano-multimodal visual ionotronic sensors for strain and temperature sensing with highly stable and reproducible electrical response over 20 000 cycles are fabricated, showing synergistically optical and electrical output performances.

Hydrogen Bonding Competition Mediated Phase Separation with Abnormal Moisture-Induced Stiffness Boosting.

Moisture usually deteriorates polymers' mechanical performance owing to its plasticizing effect, causing side effects in their practical load-bearing applications. Herein, a simple binary ionogel consisting of an amphiphilic polymer network and a hydrophobic ionic liquid (IL) is developed with remarkable stiffening effect after moisture absorption, demonstrating a complete contrast to water-induced softening effect of most polymer materials. Such a moisture-induced stiffening behavior is induced by phase separation after hydration of this binary ionogel. Specifically, it is revealed that hydrogen (H)-bonding structures play a dominant role in the humidity-responsive behavior of the ionogel, where water will preferentially interact with polymer chains through H-bonding and break the polymer-IL H-bonds, thus leading to phase separation structures with modulus boosting. This work may provide a facile and effective molecular engineering route to construct mechanically adaptive polymers with water-induced dramatic stiffening for diverse applications.

Salt-Adaptively Conductive Ionogel Sensor for Marine Sensing.

Hydrophobic ionogel has attracted much attention in underwater sensing as the artificial electronic skins and wearable sensors. However, when the low conductive ionogel-based sensor works in the marine environment, the salty seawater weakens its sensing performance, which is difficult to recognize. Herein, a salt-adaptively conductive ionogel with high submarine strain sensitivity is reported. Based on the preliminary improvement via the proton conduction mechanism, the conductivity of the ionogel further increases with the surrounding salinity rising up since the salt-induced dissociation phenomenon, which is described as the environmental salt-adaptive feature. In seawater, the conductivity of the ionogel is as high as 2.90 × 10-1 S m-1 . Significantly, with its long-term underwater stability and adhesion, the resultant ionogel-based sensor features prominent strain sensing performance (gauge factor: 1.12) while combining with various soft actuators in the marine environment. The ionogel-based sensor is capable of monitoring human breath frequency, human actions, and the locomotion of soft actuators, demonstrating its great potential in diving detection and intelligent preceptive soft robotics for marine environmental protection and exploration.

Skin-Inspired, Highly Sensitive, Broad-Range-Response and Ultra-Strong Gradient Ionogels Prepared by Electron Beam Irradiation.

Skin, characterized by its distinctive gradient structure and interwoven fibers, possesses remarkable mechanical properties and highly sensitive attributes, enabling it to detect an extensive range of stimuli. Inspired by these inherent qualities, a pioneering approach involving the crosslinking of macromolecules through in situ electron beam irradiation (EBI) is proposed to fabricate gradient ionogels. Such a design offers remarkable mechanical properties, including excellent tensile properties (>1000%), exceptional toughness (100 MJ m-3), fatigue resistance, a broad temperature range (-65-200°C), and a distinctive gradient modulus change. Moreover, the ionogel sensor exhibits an ultra-fast response time (60 ms) comparable to skin, an incredibly low detection limit (1 kPa), and an exceptionally wide detection range (1 kPa-1 MPa). The exceptional gradient ionogel material holds tremendous promise for applications in the field of smart sensors, presenting a distinct strategy for fabricating flexible gradient materials.

A Strong and Highly Transparent Ionogel Electrolyte Enabled by In Situ Polymerization-Induced Microphase Separation for High-Performance Electrochromic Devices.

Electrochromic devices built with ionogel electrolytes are seen as a pivotal step toward the future of quasi-solid electrochromic devices, due to their striking properties like exceptional safety and high ionic conductivity. Yet, the poor mechanical strength of electrolyte of these devices remains a constraint that hampers their advancement. As a resolution, this research explores the use of a robust, transparent ionogel electrolyte, which is designed using an in situ microphase separation strategy. The ionogels are highly transparent and robust and exhibit excellent physicochemical stability, including a wide electrochemical window and high temperature tolerance. Benefitting from these properties, a high-performance electrochromic device is fabricated through in situ polymerization with the ionogels, PPRODOT as the electrochromic layer, and PEDOT: PSS as the ion storage layer, achieving high transmittance contrast (43.1%), fast response (1/1.7 s), high coloring efficiency (1296.4 cm2 C-1), and excellent cycling endurance (>99.9% retention after 2000 cycles). In addition, using ITO-poly(ethylene terephthalate) as flexible substrates, a deformable electrochromic device displaying high stability is realized, highlighting the potential use in functional wearables.

Human Skin-Mimicking Ionogel-Based Electronic Skin for Intelligent Robotic Sorting.

Creating bionic intelligent robotic systems that emulate human-like skin perception presents a considerable scientific challenge. This study introduces a multifunctional bionic electronic skin (e-skin) made from polyacrylic acid ionogel (PAIG), designed to detect human motion signals and transmit them to robotic systems for recognition and classification. The PAIG is synthesized using a suspension of liquid metal and graphene oxide nanosheets as initiators and cross-linkers. The resulting PAIGs demonstrate excellent mechanical properties, resistance to freezing and drying, and self-healing capabilities. Functionally, the PAIG effectively captures human motion signals through electromechanical sensing. Furthermore, a bionic intelligent sorting robot system is developed by integrating the PAIG-based e-skin with a robotic manipulator. This system leverages its ability to detect frictional electrical signals, enabling precise identification and sorting of materials. The innovations presented in this study hold significant potential for applications in artificial intelligence, rehabilitation training, and intelligent classification systems.

Jellyfish-Inspired Polyurea Ionogel with Mechanical Robustness, Self-Healing, and Fluorescence Enabled by Hyperbranched Cluster Aggregates.

Ionogels are promising for soft iontronics, with their network structure playing a pivotal role in determining their performance and potential applications. However, simultaneously achieving mechanical toughness, low hysteresis, self-healing, and fluorescence using existing network structures is challenging. Drawing inspiration from jellyfish, we propose a novel hierarchical crosslinking network structure design for in situ formation of hyperbranched cluster aggregates (HCA) to fabricate polyurea ionogels to overcome these challenges. Leveraging the disparate reactivity of isocyanate groups, we induce the in situ formation of HCA through competing reactions, enhancing toughness and imparting the clustering-triggered emission of ionogel. This synergy between supramolecular interactions in the network and plasticizing effect in ionic liquid leads to reduced hysteresis of the ionogel. Furthermore, the incorporation of NCO-terminated prepolymer with dynamic oxime-urethane bonds (NPU) enables self-healing and enhances stretchability. Our investigations highlight the significant influence of HCA on ionogel performance, showcasing mechanical robustness including high strength (3.5 MPa), exceptional toughness (5.5 MJ m-3), resistance to puncture, and low hysteresis, self-healing, as well as fluorescence, surpassing conventional dynamic crosslinking approaches. This network design strategy is versatile and can meet the various demands of flexible electronics applications.

Healable, Recyclable, and Upcyclable Gel Membranes for Efficient Carbon Dioxide Separation.

Ionic liquids (ILs) are prized for their selective dissolution of carbon dioxide (CO2), leading to their widespread use in ionogel membranes for gas separation. Despite their advantages, creating sustainable ionogel membranes with high IL contents poses challenges due to limited mechanical strength, leakage risks, and poor recyclability. Herein, we leverage copolymerized and supramolecularly bound ILs to develop ionogel membranes with high mechanical strength, zero leakage, and excellent self-healing and recycling capabilities. These membranes exhibit superior ideal selectivity for gas separation compared to other reported ionogel membranes, achieving a CO2/nitrogen selectivity of 61.7 and a CO2/methane selectivity of 24.6, coupled with an acceptable CO2 permeability of 186.4 Barrer. Additionally, these gas separation ionogel membranes can be upcycled into ionic skins for sensing applications, further enhancing their utility. This research outlines a strategic approach to molecularly engineer ionogel membranes, offering a promising pathway for developing sustainable, high-performance materials for advanced gas separation technologies.

Deep Eutectic Solvents-based Ionogels with Ultrafast Gelation and High Adhesion in Harsh Environments.

Adhesive materials have recently drawn intensive attention due to their excellent sealing ability, thereby stimulating advances in materials science and industrial usage. However, reported adhesives usually exhibit weak adhesion strength, require high pressure for strong bonding, and display severe adhesion deterioration in various harsh environments. In this work, instead of water or organic solvents, a deep eutectic solution (DES) was used as the medium for photopolymerization of zwitterionic and polarized monomers, thus generating a novel ionogel with tunable mechanical properties. Multiple hydrogen bonds and electrostatic interactions between DES and monomers facilitated ultrafast gelation and instant bonding without any external pressure, which was rarely reported previously. Furthermore, high adhesion in different harsh environments (e.g., water, acidic and basic buffers, and saline solutions) and onto hydrophilic (e.g., glass and tissues) and hydrophobic (e.g., polymethyl methacrylate, polystyrene, and polypropylene) adherends was demonstrated. Also, high stretchability of the ionogel at extreme temperatures (-80 and 80 °C) indicated its widespread applications. Furthermore, the biocompatible ionogel showed high burst pressure onto stomach and intestine tissues to prevent liquid leakage, highlighting its potential as an adhesive patch. This ionogel provides unprecedented opportunities in the fields of packaging industry, marine engineering, medical adhesives, and electronic assembly.

Cross-Link-Dependent Ionogel-Based Triboelectric Nanogenerators with Slippery and Antireflective Properties.

Given the ability to convert various ambient unused mechanical energies into useful electricity, triboelectric nanogenerators (TENGs) are gaining interest since their inception. Recently, ionogel-based TENGs (I-TENGs) have attracted increasing attention because of their excellent thermal stability and adjustable ionic conductivity. However, previous studies on ionogels mainly pursued the device performance or applications under harsh conditions, whereas few have investigated the structure-property relationships of components to performance. The results indicate that the ionogel formulation-composed of a crosslinking monomer with an ionic liquid-affects the conductivity of the ionogel by modulating the cross-link density. In addition, the ratio of cross-linker to ionic liquid is important to ensure the formation of efficient charge channels, yet increasing ionic liquid content delivers diminishing returns. The ionogels are then used in I-TENGs to harvest water droplet energy and the performance is correlated to the ionogels structure-property relationships. Improvement of the energy harvesting is further explored by the introduction of surface polymer brushes on I-TENGs via a facile and universal method, which enhances droplet sliding by means of ideal surface contact angle hysteresis and improves its anti-reflective properties by employing the I-TENG as a surface covering for solar cells.

An All-Solid-State Flexible Supercapacitor Based on MXene/MSA Ionogel and Polyaniline Electrode with Wide Temperature Range, High Stability, and High Energy Density.

In this study, an ionogel electrolyte (PAIM-X) consisting of 1-vinyl-3-methylimidazole bis (trifluoromethyl sulfonyl) imide ([VMIM][TFSI]), Polyacrylamide (PAAm), and MXene were prepared. The conductivity of PAIM-X and integral area of the voltammetric curve of the supercapacitor (PAIMSC) were improved by adding MXene. The addition of [VMIM][TFSI] enhanced the conductivity and applicable temperature of the ionogel electrolyte. At 90 °C, the conductivity of PAIM-4 can reach 36.4 mS/cm. In addition, spherical polyaniline with good electrochemical properties was synthesized and coated on graphite paper as an active substance. An all-solid-state supercapacitor was composed of PAIM-4, polyaniline electrode with 1.2 V potential window, pseudo-capacitors and high quality capacitors. The solvent 1-ethyl-3-methylimidazolium bis (trifluoromethyl sulfonyl imide) ([EMIM][TFSI]) and methanesulfonic acid (MSA) were introduced into the ionogel to promote the redox reaction of polyaniline (PANI). The mass specific capacitance of PAIMSC was 204.6 F/g and its energy density could reach 40.92 Wh/kg, which shows great potential for practical application at high temperature. The device had good rate performance and cycle performance, and its capacitance retention rate was still 91.56% after 10,000 cycles. In addition, the supercapacitor can work within the temperature range of -20 °C to 90 °C. These excellent electrochemical properties indicate that PAAm/IL/Mxene-X has broad application space and prospect.

Investigating the Correlation between Electrolyte Concentration and Electrochemical Properties of Ionogels.

Ionogels are hybrid materials comprising an ionic liquid confined within a polymer matrix. They have garnered significant interest due to their unique properties, such as high ionic conductivity, mechanical stability, and wide electrochemical stability. These properties make ionogels suitable for various applications, including energy storage devices, sensors, and solar cells. However, optimizing the electrochemical performance of ionogels remains a challenge, as the relationship between specific capacitance, ionic conductivity, and electrolyte solution concentration is yet to be fully understood. In this study, we investigate the impact of electrolyte solution concentration on the electrochemical properties of ionogels to identify the correlation for enhanced performance. Our findings demonstrate a clear relationship between the specific capacitance and ionic conductivity of ionogels, which depends on the availability of mobile ions. The reduced number of ions at low electrolyte solution concentrations leads to decreased ionic conductivity and specific capacitance due to the scarcity of a double layer, constraining charge storage capacity. However, at a 31 vol% electrolyte solution concentration, an ample quantity of ions becomes accessible, resulting in increased ionic conductivity and specific capacitance, reaching maximum values of 58 ± 1.48 µS/cm and 45.74 F/g, respectively. Furthermore, the synthesized ionogel demonstrates a wide electrochemical stability of 3.5 V, enabling diverse practical applications. This study provides valuable insights into determining the optimal electrolyte solution concentration for enhancing ionogel electrochemical performance for energy applications. It highlights the impact of ion pairs and aggregates on ion mobility within ionogels, subsequently affecting their resultant electrochemical properties.

Ultra-Tough and Recyclable Ionogels Constructed by Coordinated Supramolecular Solvents.

The mechanical properties of most hydrogels (ionogels) are considerably affected by covalently cross-linked networks. However, the interactions between solvent/solvent molecules and solvent/polymer chains are usually ignored. Herein, a series of ultra-tough ionogels were prepared via a supramolecular solvent, halometallate ionic liquid, in which cations and coordinating anions form a 3D supramolecular network. The linear polymer chains are physically cross-linked with supramolecular solvents synergistically enhancing the strength (14.3 MPa), toughness (78 MJ m-3 ), and Young's modulus (55 MPa) of ionogels, effectively dispersing the stress concentration under load, and obtaining better fatigue resistance and higher fracture energy (198 kJ m-2 ). Furthermore, the reversible cross-linking enables green recovery and recycling of ionogels, simply by water. This strategy shows broad applicability based on a variety of supramolecular solvents and coordinatable polymers.

Bioinspired Photonic Ionogels as Interactively Visual Ionic Skin with Optical and Electrical Synergy.

With the ever-growing demands for flexible smart interactive electronics, it remains highly desirable yet challenging to design and fabricate interactive ionic skin with multiple signal synergistic outputs. Herein, high-performance photonic ionogels (PIGs) with excellent stability and synergy sensitivity are designed by locking a non-volatile and non-hygroscopic ionic liquid (IL), that is, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([EMIm][TFSI]), into photonic elastomers based on polymer networks of poly(ethylene glycol) phenyl ether acrylate (PEGPEA). Through manipulating the degree of crosslinking, PIGs exhibit high sensitivity that can output distinct and intuitive color change in visual with the mechanochromic sensitivity of ≈1.76 nm per percent strain and clear electrical signal with the gauge factor of 1, in response to a tiny stretch of millimeter scale. Thanks to the stable photonic elastomers and IL employed, the PIGs developed in this study exhibit good performance under harsh and complex environmental conditions, including high/low temperature (from -35 °C to 100 °C), dry/wet air, and high vacuum. This study provides a novel strategy for developing integrated, stable, and multifunctional photonic ionogels for ionic skin sensors and flexible interactive devices with synergistically optical and electrical output.

Chemical Vapor Deposition of Ionic Liquids for the Fabrication of Ionogel Films and Patterns.

Film deposition and high-resolution patterning of ionic liquids (ILs) remain a challenge, despite a broad range of applications that would benefit from this type of processing. Here, we demonstrate for the first time the chemical vapor deposition (CVD) of ILs. The IL-CVD method is based on the formation of a non-volatile IL through the reaction of two vaporized precursors. Ionogel micropatterns can be easily obtained via the combination of IL-CVD and standard photolithography, and the resulting microdrop arrays can be used as microreactors. The IL-CVD approach will facilitate leveraging the properties of ILs in a range of applications and microfabricated devices.

Imidazole-based ionogel as room temperature benzene and formaldehyde sensor.

A room temperature benzene and formaldehyde gas sensor system with an ionogel as sensing material is presented. The sensing layer is fabricated employing poly(N-isopropylacrylamide) polymerized in the presence of 1-ethyl-3-methylimidazolium ethyl sulfate ionic liquid onto gold interdigitated electrodes. When the ionogel is exposed to increasing formaldehyde concentrations employing N2 as a carrier gas, a more stable response is observed in comparison to the bare ionic liquid, but no difference in sensitivity occurs. On the other hand, when air is used as carrier gas the sensitivity of the system towards formaldehyde is decreased by one order of magnitude. At room temperature, the proposed sensor exhibited in air higher sensitivities to benzene, at concentrations ranging between 4 and 20 ppm resulting, in a limit of detection of 47 ppb, which is below the standard permitted concentrations. The selectivity of the IL towards HCHO and C6H6 is demonstrated by the absence of response when another IL is employed. Humidity from the ambient air slightly affects the resistance of the system proving the protective role of the polymeric matrix. Furthermore, the gas sensor system showed fast response/recovery times considering the thickness of the material, suggesting that ionogel materials can be used as novel and highly efficient volatile organic compounds sensors operating at room temperature.Graphical abstract.

The Electric Field Responses of Inorganic Ionogels and Poly(ionic liquid)s.

Ionic liquids (ILs) are a class of pure ions with melting points lower than 100 °C. They are getting more and more attention because of their high thermal stability, high ionic conductivity and dielectric properties. The unique dielectric properties aroused by the ion motion of ILs makes ILs-contained inorganics or organics responsive to electric field and have great application potential in smart electrorheological (ER) fluids which can be used as the electro-mechanical interface in engineering devices. In this review, we summarized the recent work of various kinds of ILs-contained inorganic ionogels and poly(ionic liquid)s (PILs) as ER materials including their synthesis methods, ER responses and dielectric analysis. The aim of this work is to highlight the advantage of ILs in the synthesis of dielectric materials and their effects in improving ER responses of the materials in a wide temperature range. It is expected to provide valuable suggestions for the development of ILs-contained inorganics and PILs as electric field responsive materials.

Self-Healing, Adhesive, and Highly Stretchable Ionogel as a Strain Sensor for Extremely Large Deformation.

Fabricating a strain sensor that can detect large deformation over a curved object with a high sensitivity is crucial in wearable electronics, human/machine interfaces, and soft robotics. Herein, an ionogel nanocomposite is presented for this purpose. Tuning the composition of the ionogel nanocomposites allows the attainment of the best features, such as excellent self-healing (>95% healing efficiency), strong adhesion (347.3 N m-1 ), high stretchability (2000%), and more than ten times change in resistance under stretching. Furthermore, the ionogel nanocomposite-based sensor exhibits good reliability and excellent durability after 500 cycles, as well as a large gauge factor of 20 when it is stretched under a strain of 800-1400%. Moreover, the nanocomposite can self-heal under arduous conditions, such as a temperature as low as -20 °C and a temperature as high as 60 °C. All these merits are achieved mainly due to the integration of dynamic metal coordination bonds inside a loosely cross-linked network of ionogel nanocomposite doped with Fe3 O4 nanoparticles.