A gas-plastic elastomer that quickly self-heals damage with the aid of CO2 gas

Biomass and Transparent Supramolecular Elastomers for Green Electronics Enabled by the Controlled Growth and Self-Assembly of Dynamic Polymer Networks

Determining the optimal method for preparing supramolecular materials remains a profound challenge. This process requires a combination of renewable raw materials to create supramolecular materials with multiple functions and properties, including simple fabrication, sustainability, a dynamic nature, good toughness, and transparency. In this work, a strategy is presented for toughening supramolecular networks based on solid-phase chain extension. This toughening strategy is simple and environmentally friendly. In addition, a series of biobased elastomers are designed and prepared with adjustable performance characteristics. This strategy can significantly improve the transparency, tensile strength, and toughness of the synthesized elastomer. The synthesized biobased elastomers have great ductility, repairability, and recyclability, and they show good adhesion and dielectric properties. A biobased ionic skin is assembled from these biobased elastomers. Assembled ionic skin can sensitively detect external stimuli (such as stretching, bending, compression, or temperature changes) and monitor human movement. The conductive and dielectric layers of the biobased ionic skin are both obtained from renewable raw materials. This research provides novel molecular design approaches and material selection methods for promoting the development of green electronic devices and biobased elastomers.

Covalent adaptable polymer networks with CO2-facilitated recyclability

Cross-linked polymers with covalent adaptable networks (CANs) can be reprocessed under external stimuli owing to the exchangeability of dynamic covalent bonds. Optimization of reprocessing conditions is critical since increasing the reprocessing temperature costs more energy and even deteriorates the materials, while reducing the reprocessing temperature via molecular design usually narrows the service temperature range. Exploiting CO2 gas as an external trigger for lowering the reprocessing barrier shows great promise in low sample contamination and environmental friendliness. Herein, we develop a type of CANs incorporated with ionic clusters that achieve CO2-facilitated recyclability without sacrificing performance. The presence of CO2 can facilitate the rearrangement of ionic clusters, thus promoting the exchange of dynamic bonds. The effective stress relaxation and network rearrangement enable the system with rapid recycling under CO2 while retaining excellent mechanical performance in working conditions. This work opens avenues to design recyclable polymer materials with tunable dynamics and responsive recyclability.

Effect of ion distribution on stress relaxation in polyelectrolyte complex gels

Solutions of polyelectrolytes consisting of polycations and polyanions in equal proportions were studied in the present work. Due to the physical cross-links formed by the charged groups, physical gels were formed in such systems. The mechanical properties and structure of the obtained gels depending on the charge arrangement along the backbone and the dimensionless Bjerrum length λ were investigated. The response of the systems to a uniaxial affine deformation was studied first. It was found that the systems can be divided into three groups depending on the charge arrangement: showing an almost elastic response; showing a viscoelastic response with a very long relaxation time; and showing a weak viscoelastic response with a short relaxation time. Interestingly, no stable aggregates were formed in the systems with the charges located on spacers, probably because of the increased mobility of the charges in such systems. The obtained stress relaxation curves had different functional forms, indicating that the relaxation has at least two characteristic times, which are different for different systems. In order to understand the molecular nature of the observed mechanical response, the temporal evolution of the network structure of a system showing a viscoelastic response with a very long relaxation time was studied; the aggregates were found to be dynamic, which leads to the relaxation of the "subchains" conformation.

CO2 switchable adhesion of ionic polydimethylsiloxane elastomers

We have developed ionic polydimethylsiloxane elastomers that rapidly and reversibly increase their adhesion upon exposure to carbon dioxide (CO2) gas. The CO2 molecules dissolve quickly into the ionic aggregates, physically crosslinking the polymer chains and plasticizing them. The elastomer consequently becomes softer and more adhesive upon exposure to CO2.

Highly Stretchable Stress-Strain Sensor from Elastomer Nanocomposites with Movable Cross-links and Ketjenblack

Practical applications like very thin stress-strain sensors require high strength, stretchability, and conductivity, simultaneously. One of the approaches is improving the toughness of the stress-strain sensing materials. Polymeric materials with movable cross-links in which the polymer chain penetrates the cavity of cyclodextrin (CD) demonstrate enhanced strength and stretchability, simultaneously. We designed two approaches that utilize elastomer nanocomposites with movable cross-links and carbon filler (ketjenblack, KB). One approach is mixing SC (a single movable cross-network material), a linear polymer (poly(ethyl acrylate), PEA), and KB to obtain their composite. The electrical resistance increases proportionally with tensile strain, leading to the application of this composite as a stress-strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other approach is a composite made with KB and a movable cross-network elastomer for knitting dissimilar polymers (KP), where movable cross-links connect the CD-modified polystyrene (PSCD) and PEA. The obtained composite acts as a highly sensitive stress-strain sensor that exhibits an exponential increase in resistance with increasing tensile strain due to the polymer dethreading from the CD rings. The designed preparations of highly repeatable or highly responsive stress-strain sensors with good mechanical properties can help broaden their application in electrical devices.

Integrated Extrinsic and Intrinsic Self-Healing of Polysiloxane Materials by Cleavable Molecular Cages Encapsulating Fluoride Ions

Self-healing ability is crucial to increasing the lifetime and reliability of materials. In this study, spatiotemporal control of the healing of a polysiloxane material is achieved using a cleavable cage compound encapsulating a fluoride ion (F- ), which triggeres the dynamic rearrangement of the siloxane (Si-O-Si) networks. A self-healing siloxane-based elastomer is prepared by cross-linking polydimethylsiloxane (PDMS) with a F- -encapsulating cage-type germoxane (Ge-O-Ge) compound. This material can self-heal repeatedly under humid conditions. The F- released by hydrolytic cleavage of the cage framework contributes to rejoining of the cut pieces by promoting the local rearrangement of the siloxane networks. The use of a molecular cage encapsulating a catalyst for dynamic bond rearrangement provides a new concept for designing self-healing polysiloxane materials based on integrated extrinsic and intrinsic mechanisms.

Dual Reversible Network Nanoarchitectonics for Ultrafast Light-Controlled Healable and Tough Polydimethylsiloxane-Based Composite Elastomers

It is highly desirable to develop polydimethylsiloxane (PDMS) elastomers with high self-healing efficiency and excellent mechanical properties. However, most self-healable materials reported to date still take several hours to self-heal and improving the self-healing property often comes at the expense of mechanical properties. Herein, a simple design strategy of dual reversible network nanoarchitectonics is reported for constructing ultrafast light-controlled healable (40 s) and tough (≈7.2 MJ m-3) PDMS-based composite elastomers. The rupture reconstruction of dynamic bonds and the reinforcement effect of carbon nanotubes (10 wt %) endowed our composite elastomer with excellent fracture toughness that originated from a good yield strength (≈1.1 MPa) and stretchability (≈882%). Moreover, carbon nanotubes can quickly and directly heat the damaged area of the composite to achieve its ultrafast repair with the assistance of dynamic polymer/filler interfacial interaction, greatly shortening the self-healing time (12 h). The self-healing performance is superior to that of reported self-healable PDMS-based materials. This novel strategy and the as-prepared supramolecular elastomer can inspire further various practical applications, such as remote anti-icing/deicing materials.

Autonomous Healable Elastomers with High Elongation, Stiffness, and Fatigue Resistance

Although self-healing elastomers have been developed in a great breakthrough, it is still a challenge to develop one kind of material that can respond to the fracture instantly even though this characteristic plays an essential role in emergency circumstances. Herein, we adopt free radical polymerization to construct one polymer network equipped with two weak interactions (dipole-dipole interaction and hydrogen bonding). The elastomer we synthesized has a high self-healing efficiency (100%) and a very short healing time (3 min) in an air atmosphere, and it can also self-heal in seawater, showing an ideal healing efficiency of >80%. Additionally, on account of its high elongation (>1000%) and antifatigue capacity (no rupture after loading-unloading 2000 times), the elastomer can be utilized in a wide range of applications, including e-skin and soft robot fields.

Toughening Ionic Polymer Using Bulky Alkylammonium Counterions and Comb Architecture

Ionic interactions in ionic polymers, such as ionomers, polyelectrolytes, and polyampholytes, contribute to toughness in systems with high mobility and active ion dynamics, such as hydrogels and elastomers. However, it remains challenging to toughen rigid polymers through ionic interactions without lowering their elastic modulus through plasticization. Here, we present a strategy for toughening without sacrificing the elastic modulus by combining a comb polymer with bulky ammonium counterions. We designed and synthesized ionic comb polymers with oligoethylene glycol side chains and carboxylic acids in each monomer unit of the polynorbornene backbone, neutralized by trialkylamines, ranging from ethyl to octyl. The counterion size in ionic comb polymers influenced the mechanical properties of tensile testing─not the elongation at break and the elastic modulus but the ultimate strength and toughness. The ionic comb polymer containing heptylammonium counterions displayed the highest toughness of 77 MJ m^-3. Tensile studies at various strain rates demonstrated a rate-dependent difference between heptyl- and octylammonium counterions. This result suggests that the heptylammonium counterion acted as a sacrificial bond by providing a moderate dissociation rate that was slightly slower than that of the octylammonium counterion, leading to toughening.

Overcoming the entropy of polymer chains by making a plane with terminal groups: a thermoplastic PDMS with a long-range 1D structural order

Due to its unique physical and chemical properties, polydimethylsiloxane (PDMS) is widely used in many applications, in which covalent cross-linking is commonly used to cure the fluidic polymer. The formation of a non-covalent network achieved through the incorporation of terminal groups that exhibit strong intermolecular interactions has also been reported to improve the mechanical properties of PDMS. Through the design of a terminal group capable of two-dimensional (2D) assembly, rather than the generally used multiple hydrogen bonding motifs, we have recently demonstrated an approach for inducing long-range structural ordering of PDMS, resulting in a dramatic change in the polymer from a fluid to a viscous solid. Here we present an even more surprising terminal-group effect: simply replacing a hydrogen with a methoxy group leads to extraordinary enhancement of the mechanical properties, giving rise to a thermoplastic PDMS material without covalent cross-linking. This finding would update the general notion that less polar and smaller terminal groups barely affect polymer properties. Based on a detailed study of the thermal, structural, morphological and rheological properties of the terminal-functionalized PDMS, we revealed that 2D assembly of the terminal groups results in networks of PDMS chains, which are arranged as domains with long-range one-dimensional (1D) periodic order, thereby increasing the storage modulus of the PDMS to exceed its loss modulus. Upon heating, the 1D periodic order is lost at around 120 °C, while the 2D assembly is maintained up to ∼160 °C. The 2D and 1D structures are recovered in sequence upon cooling. Due to the thermally reversible, stepwise structural disruption/formation as well as the lack of covalent cross-linking, the terminal-functionalized PDMS shows thermoplastic behavior and self-healing properties. The terminal group presented herein, which can form a 'plane', might also drive other polymers to assemble into a periodically ordered network structure, thereby allowing for significant modulation of their mechanical properties.

Surface Hydrophobization Provides Hygroscopic Supramolecular Plastics Based on Polysaccharides with Damage-Specific Healability and Room-Temperature Recyclability

Supramolecular materials with room-temperature healability and recyclability are highly desired because they can extend materials lifetimes and reduce resources consumption. Most approaches toward healing and recycling rely on the dynamically reversible supramolecular interactions, such as hydrogen, ionic and coordinate bonds, which are hygroscopic and vulnerable to water. The general water-induced plasticization facilitates the healing and reprocessing process but cause a troubling problem of random self-adhesion. To address this issue, here it is reported that by modifying the hygroscopic surfaces with hydrophobic alkyl chains of dodecyltrimethoxysilane (DTMS), supramolecular plastic films based on commercial raw materials of sodium alginate (SA) and cetyltrimethylammonium bromide (CTAB) display extraordinary damage-specific healability. Owing to the hydrophobic surfaces, random self-adhesion is eliminated even under humid environment. When damage occurs, the fresh surfaces with ionic groups and hydroxyl groups expose exclusively at the damaged site. Thus, damage-specific healing can be readily facilitated by water-induced plasticization. Moreover, the films display excellent room-temperature recyclability. After multiple times of reprocessing and re-modifying with DTMS, the rejuvenated films exhibit fatigueless mechanical properties. It is anticipated that this approach to damage-specific healing and room-temperature recycling based on surface hydrophobization can be applied to design various of supramolecular plastic polysaccharides materials for building sustainable societies.

Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

Highly stretchable ionically crosslinked acrylate elastomers inspired by polyelectrolyte complexes

Dynamic bonds are a powerful approach to tailor the mechanical properties of elastomers and introduce shape-memory, self-healing, and recyclability. Among the library of dynamic crosslinks, electrostatic interactions among oppositely charged ions have been shown to enable tough and resilient elastomers and hydrogels. In this work, we investigate the mechanical properties of ionically crosslinked ethyl acrylate-based elastomers assembled from oppositely charged copolymers. Using both infrared and Raman spectroscopy, we confirm that ionic interactions are established among polymer chains. We find that the glass transition temperature of the complex is in between the two individual copolymers, while the complex demonstrates higher stiffness and more recovery, indicating that ionic bonds can strengthen and enhance recovery of these elastomers. We compare cycles to increasing strain levels at different strain rates, and hypothesize that at fast strain rates ionic bonds dynamically break and reform while entanglements do not have time to slip, and at slow strain rates ionic interactions are disrupted and these entanglements slip significantly. Further, we show that a higher ionic to neutral monomer ratio can increase the stiffness, but its effect on recovery is minimal. Finally, taking advantage of the versatility of acrylates, ethyl acrylate is replaced with the more hydrophilic 2-hydroxyethyl acrylate, and the latter is shown to exhibit better recovery and self-healing at a cost of stiffness and strength. The design principles uncovered for these easy-to-manufacture polyelectrolyte complex-inspired bulk materials can be broadly applied to tailor elastomer stiffness, strength, inelastic recovery, and self-healing for various applications.

Repulsive segregation of fluoroalkyl side chains turns a cohesive polymer into a mechanically tough, ultrafast self-healable, nonsticky elastomer

Dynamic crosslinking of flexible polymer chains via attractive and reversible interactions is widely employed to obtain autonomously self-healable elastomers. However, this design leads to a trade-off relationship between the strength and self-healing speed of the material, i.e., strong crosslinks provide a mechanically strong elastomer with slow self-healing property. To address this issue, we report an "inversion" concept, in which attractive poly(ethyl acrylate-random-methyl acrylate) chains are dynamically crosslinked via repulsively segregated fluoroalkyl side chains attached along the main chain. The resulting elastomer self-heals rapidly (> 90% within 15 min) via weak but abundant van der Waals interactions among matrix polymers, while the dynamic crosslinking provides high fracture stress (≈2 MPa) and good toughness (≈17 MJ m^-3). The elastomer has a nonsticky surface and selectively self-heals only at the damaged faces due to the surface segregation of the fluoroalkyl chains. Moreover, our elastomer strongly adheres to polytetrafluoroethylene plates (≈60 N cm^-2) via hot pressing.

Effect of alkali metal cations on network rearrangement in polyisoprene ionomers

The effects of cations, Li⁺, Na⁺, and Cs⁺, on the structure of ionic aggregates and network rearrangement in carboxylated polyisoprene (PI) ionomers were studied. We found that network rearrangement via interaggregate hopping of metal carboxylates is improved with a decrease in cation size, even though density functional theory (DFT) calculation indicated the increase in the attractive interaction between metal carboxylates. At the same time, we also found that as the size of the cation decreases, the inclusion of the PI segment in the ionic aggregate increases. The DFT calculation suggested the cation-π interaction between the cation and double bonds in the PI segment as the cause for the inclusion. The inclusion of the PI segment with a low glass transition temperature (T_g) plasticizes the ionic aggregate and would sterically hinder the attractive interaction between metal carboxylates. In fact, the electron spin resonance measurement revealed a decrease in the T_g of the ionic aggregate with a decrease in cation size. Based on our findings, we proposed that the inclusion of PI segments in the ionic aggregate is the possible cause for the enhancement of network rearrangement in the carboxylated PI ionomers with a decrease in the cation size.

Synergetic improvement in the mechanical properties of polyurethanes with movable crosslinking and hydrogen bonds

Polyurethane (PU) materials with movable crosslinking were prepared by a typical two-step synthetic process using an acetylated γ-cyclodextrin (TAcγCD) diol compound. The soft segment of PU is polytetrahydrofuran (PTHF), and the hard segment consists of hexamethylene diisocyanate (HDI) and 1,3-propylene glycol (POD). The synthesized PU materials exhibited the typical mechanical characteristics of a movable crosslinking network, and the presence of hydrogen bonds from the urethane bonds resulted in a synergistic effect. Two kinds of noncovalent bond crosslinking increased the Young's modulus of the material without affecting its toughness. Fourier transform infrared spectroscopy and X-ray scattering measurements were performed to analyze the effect of introducing movable crosslinking on the internal hydrogen bond and the microphase separation structure of PU, and the results showed that the carbonyl groups on TAcγCD could form hydrogen bonds with the PU chains and that the introduction of movable crosslinking weakened the hydrogen bonds between the hard segments of PU. When stretched, the movable crosslinking of the PU materials suppressed the orientation of polymer chains (shish-kebab orientation) in the tensile direction. The mechanical properties of the movable crosslinked PU materials show promise for future application in the industrial field.

Highly Impact-Resistant Block Polymer-Based Thermoplastic Elastomers with an Ionically Functionalized Rubber Phase

There has been a great deal of interest in incorporating noncovalent bonding groups into elastomers to achieve high strength. However, the impact resistance of such elastomers has not been evaluated, even though it is a crucial mechanical property in practical usage, partly because a large-scale synthetic scheme has not been established. By ionizing the rubber component in polystyrene-b-polyisoprene-b-polystyrene (SIS), we prepared several tens of grams of SIS-based elastomers with an ionically functionalized rubber phase and a sodium cation (i-SIS(Na)) or a bulky barium cation (i-SIS(Ba)). The i-SIS(Na) and i-SIS(Ba) exhibited very high tensile toughness of 520 and 280 MJ m-3, respectively. They also exhibited excellent compressive resistance. Moreover, i-SIS(Ba) was demonstrated to have a higher impact resistance, that is, more protective of a material being covered compared to covering by typical high-strength glass fiber-reinforced plastic. As such elastomers can be produced at an industrial scale, they have great market potential as next-generation elastomeric materials.

Mechanically Strong, Autonomous Self-Healing, and Fully Recyclable Silicone Coordination Elastomers with Unique Photoluminescent Properties

The combination of excellent mechanical performances, high reprocess efficiency, and wide-range tunability for functional dynamic siloxane materials is a challenging subject. Herein, the fabrication of mechanically strong, autonomous self-healing, and fully recyclable silicone elastomers with unique photoluminescent properties by coordination of poly(dimethylsiloxane) (PDMS) containing coordination bonding motifs with Zn²⁺ ions is reported. Salicylaldimine groups, which are introduced into the polysiloxane backbone via mild Schiff-base reaction, coordinate with zinc ions to form elastomeric networks The obtained supramolecular elastomers have excellent mechanical properties, with the optimized tensile strength up to 10.0 MPa, which is unprecedented among the reported thermoplastic polysiloxane-based elastomers. Both mechanical properties and stress relaxation kinetics are tunable via adjusting the length of PDMS segments or the molar ratio of metal versus salicylaldimine. Furthermore, these elastomers can be conveniently healed and recycled to regain their original mechanical properties and integrity under mild conditions. In addition, this new kind of polysiloxane also exhibits coordination-enhanced fluorescence, showing great promise for preparing photoluminescent elastomers or coatings.

Simple linear ionic polysiloxane showing unexpected nanostructure and mechanical properties

Polysiloxanes are ubiquitous materials in industry and daily life derived from silicates, an abundant resource. They exhibit various properties, which depend on the main-chain network structure. Linear (1D backbone) polysiloxanes provide amorphous materials. They are recognized as fluid materials in the form of grease or oil with a low glass transition temperature. Herein we report that a simple linear polysiloxane, poly(3-aminopropylmethylsiloxane) hydrochloride, shows an elastic modulus comparable to that of stiff resins such as poly(tetrafluoroethylene). By introducing an ammonium salt at all the units of this polysiloxane, inter- and intramolecular ionic aggregates form, immensely enhancing the elastic modulus. This polysiloxane is highly hygroscopic, and its modulus can be altered reversibly 100 million times between moist and dry atmospheres. In addition, it works as a good adhesive for glass substrates with a shear strength of more than 1 MPa in the dry state. Despite its simple structure with a flexible backbone, this polymer unexpectedly self-assembles to form an ordered lamellar nanostructure in dry conditions. Consequently, this work reveals new functions and possibilities for polysiloxanes materials by densely introducing ionic groups.

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag+ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal-ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal-ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

Toward Robust, Tough, Self-Healable Supramolecular Elastomers for Potential Application in Flexible Substrates

A robust, tough, and self-healable elastomer is a promising candidate for substrate in flexible electronic devices, but there is often a trade-off between mechanical properties (robustness and toughness) and self-healing. Here, a poly(dimethylsiloxane) (PDMS) supramolecular elastomer is developed based on metal-coordinated bonds with relatively high activation energy. The strong metal-coordination complexes and their corresponding ionic clusters acting as the cross-linking points strengthen the resultant supramolecular networks, which achieves superior mechanical robustness (2.81 MPa), and their consecutive dynamic rupture and reconstruction efficiently dissipate strain energy during the stretching process, which leads to an impressive fracture toughness (32 MJ/m³). Additionally, the reversible intermolecular interactions (weak hydrogen bonds and strong sacrificial coordination complexes/clusters) can break and re-form upon heating; thus, the elastomer self-heals at a moderate temperature with the highest healing efficiency of 95%. As such, the potential of the as-prepared supramolecular elastomer for a substrate material of flexible electronic devices is discovered.

Self-healing elastomers based on conjugated diolefins: a review

The introduction of dynamic covalent and physical crosslinks into diolefin-based elastomers improves mechanical and self-healing properties. The presence of dynamic crosslinks also helps in the reprocessing of elastomers.

Toward strong self-healing polyisoprene elastomers with dynamic ionic crosslinks

To compromise high mechanical strength and efficient self-healing capability in an elastomer with dynamic crosslinks, optimization of the molecular structure is crucial in addition to the tuning of the dynamic properties of the crosslinks. Herein, we studied the effects of molecular weight, content of carboxy groups, and neutralization level of ionically crosslinked polyisoprene (PI) elastomers on their morphology, network rearrangement behavior, and self-healing and mechanical properties. In this PI elastomer, nanosized sphere-shaped ionic aggregates are formed by both neutralized and non-neutralized carboxy groups that act as stickers. The number density of the ionic aggregates that act as physical crosslinks increased with increase in the stickers' concentration, although the size of the ionic aggregates was independent of the molecular weight and the stickers' concentration. The ionic network was dynamically rearranged by the stickers' hopping between the ionic aggregates, and the rearrangement was accelerated by decreasing the neutralization level. We found that the 2Rg of the PI must be significantly larger than the average distance between the ionic aggregates to obtain a mechanically strong PI elastomer. We also found that further increase in the molecular weight is effective to enhance the dimensional stability of the elastomer. However, this approach reduced the elastomer's self-healing rate at the same time because the diffusion and randomization of the polymer chains between the damaged faces were reduced. In this work, we clearly demonstrated the principle in the optimization of the molecular structure for the ionically crosslinked PI elastomers to tune the mechanical and autonomous self-healing properties.

Nitric Oxide Release Device for Remote-Controlled Cancer Therapy by Wireless Charging

Traditional phototherapies face the issue that the insufficient penetration of light means it is difficult to reach deep lesions, which greatly reduces the feasibility of cancer therapy. Here, an implantable nitric oxide (NO)-release device is developed to achieve long-term, long-distance, remote-controllable gas therapy for cancer. The device consists of a wirelessly powered light-emitting diode (wLED) and S-nitrosoglutathione encapsulated with poly(dimethylsiloxane) (PDMS), obtaining the NO-release wLED (NO-wLED). It is found that NO release from the NO-wLED can be triggered by wireless charging and the concentration of produced NO reaches 0.43 × 10^-6 m min^-1 , which can achieve a killing effect on cancer cells. In vivo anticancer experiments exhibit obvious inhibitory effect on the growth of orthotopic cancer when the implanted NO-wLED is irradiated by wireless charging. In addition, recurrence of cancer can be prevented by NO produced from the NO-wLED after surgery. By illumination in the body, this strategy overcomes the poor penetration and long-wavelength dependence of traditional phototherapies, which also provides a promising approach for in vivo gas therapy remote-controlled by wireless charging.

A Self-Cross-Linking Supramolecular Polymer Network Enabled by Crown-Ether-Based Molecular Recognition

Supramolecular polymers based on host-guest molecular recognition have emerged as promising platforms for the development of smart materials. However, the studies on them are primarily conducted in solution and/or in the gel state. In contrast, little is known about dynamic properties and applications of supramolecular polymers in bulk. Herein, we present a self-cross-linking supramolecular polymer network (SPN) as a model system to understand the bulk properties controlled by noncovalent interactions. Specifically, the SPN monomer is composed of two benzo-21-crown-7 (B21C7) host units and two dialkylammonium salt guest moieties on a four-arm core, wherein complementary host-guest complexation drives the formation of the SPN with [2]pseudorotaxane linkages between B21C7 and ammonium motifs. The dynamic and reversible behaviors of the linkages are evaluated by measurement of viscoelasticity. The results indicate that the host-guest molecular recognition becomes highly dynamic at elevated temperature. Moreover, the relatively high activation energy of the SPN manifests itself as a new type of thermoplastic material with network topology freezing glass transition. Finally, we demonstrate how these findings provide insights into the malleability and processability of the SPN by simple demos. The fundamental understanding gained from the research on this SPN in bulk will facilitate the advancement and application of supramolecular materials.

Autonomous self-healing polyisoprene elastomers with high modulus and good toughness based on the synergy of dynamic ionic crosslinks and highly disordered crystals

We designed a novel polyisoprene elastomer with high mechanical properties and autonomous self-healing capability at room temperature facilitated by the coexistence of dynamic ionic crosslinks and crystalline components that slowly reassembled.

Dual-Cross-Linked Supramolecular Polysiloxanes for Mechanically Tunable, Damage-Healable and Oil-Repellent Polymeric Coatings

Polymeric coatings that show tunable mechanical strength, healing ability of mechanical damage, and proper liquid repellency will be promising in various areas across life and industry. However, the exploitation of such coating materials is largely limited by their molecular design. In this work, polymeric coatings with ion-controlled mechanics and coloration and damage-healing and oil-sliding properties have been demonstrated based on a supramolecular design of dual-cross-linked polysiloxanes. The coating color and mechanical properties can be adjusted by coordinative metal ions with various metal-ligand binding abilities. Dense and dynamic hydrogen bonds and coordination bonds lead to the ready healing ability and high durability of the coating. The extreme smoothness of the flat silicone coating facilitates not only the sliding of impinging oil but also the restoration of topological integrity from mechanical damage. The coating can be selectively patterned and applied to large-scale substrates by diverse coating operations, making it feasible for versatile applications.