Carbon Dots as Fillers Inducing Healing/Self‐Healing and Anticorrosion Properties in Polymers

Self‐healing is the way by which nature repairs damage and prolongs the life of bio entities. A variety of practical applications require self‐healing materials in general and self‐healing polymers in particular. Different (complex) methods provide the rebonding of broken bonds, suppressing crack, or local damage propagation. Here, a simple, versatile, and cost‐effective methodology is reported for initiating healing in bulk polymers and self‐healing and anticorrosion properties in polymer coatings: introduction of carbon dots (CDs), 5 nm sized carbon nanocrystallites, into the polymer matrix forming a composite. The CDs are blended into polymethacrylate, polyurethane, and other common polymers. The healing/self‐healing process is initiated by interfacial bonding (covalent, hydrogen, and van der Waals bonding) between the CDs and the polymer matrix and can be optimized by modifying the functional groups which terminate the CDs. The healing properties of the bulk polymer–CD composites are evaluated by comparing the tensile strength of pristine (bulk and coatings) composites to those of fractured composites that are healed and by following the self‐healing of scratches intentionally introduced to polymer–CD composite coatings. The composite coatings not only possess self‐healing properties but also have superior anticorrosion properties compared to those of the pure polymer coatings.     

Tough Supramolecular Polymer Networks with Extreme Stretchability and Fast Room‐Temperature Self‐Healing

Recent progress on highly tough and stretchable polymer networks has highlighted the potential of wearable electronic devices and structural biomaterials such as cartilage. For some given applications, a combination of desirable mechanical properties including stiffness, strength, toughness, damping, fatigue resistance, and self‐healing ability is required. However, integrating such a rigorous set of requirements imposes substantial complexity and difficulty in the design and fabrication of these polymer networks, and has rarely been realized. Here, we describe the construction of supramolecular polymer networks through an in situ copolymerization of acrylamide and functional monomers, which are dynamically complexed with the host molecule cucurbit[8]uril (CB[8]). High molecular weight, thus sufficient chain entanglement, combined with a small‐amount dynamic CB[8]‐mediated non‐covalent crosslinking (2.5 mol%), yields extremely stretchable and tough supramolecular polymer networks, exhibiting remarkable self‐healing capability at room temperature. These supramolecular polymer networks can be stretched more than 100× their original length and are able to lift objects 2000× their weight. The reversible association/dissociation of the host–guest complexes bestows the networks with remarkable energy dissipation capability, but also facile complete self‐healing at room temperature. In addition to their outstanding mechanical properties, the networks are ionically conductive and transparent. The CB[8]‐based supramolecular networks are synthetically accessible in large scale and exhibit outstanding mechanical properties. They could readily lead to the promising use as wearable and self‐healable electronic devices, sensors and structural biomaterials.     

A Highly Efficient Self‐Healing Elastomer with Unprecedented Mechanical Properties

It is highly desirable, although very challenging, to develop self‐healable materials exhibiting both high efficiency in self‐healing and excellent mechanical properties at ambient conditions. Herein, a novel Cu(II)–dimethylglyoxime–urethane‐complex‐based polyurethane elastomer (Cu–DOU–CPU) with synergetic triple dynamic bonds is developed. Cu–DOU–CPU demonstrates the highest reported mechanical performance for self‐healing elastomers at room temperature, with a tensile strength and toughness up to 14.8 MPa and 87.0 MJ m^?3, respectively. Meanwhile, the Cu–DOU–CPU spontaneously self‐heals at room temperature with an instant recovered tensile strength of 1.84 MPa and a continuously increased strength up to 13.8 MPa, surpassing the original strength of all other counterparts. Density functional theory calculations reveal that the coordination of Cu(II) plays a critical role in accelerating the reversible dissociation of dimethylglyoxime–urethane, which is important to the excellent performance of the self‐healing elastomer. Application of this technology is demonstrated by a self‐healable and stretchable circuit constructed from Cu–DOU–CPU.     

Highly Elastic and Ultratough Hybrid Ionic–Covalent Hydrogels with Tunable Structures and Mechanics

Hybrid ionically–covalently crosslinked double‐network (DN) hydrogels are attracting increasing attention on account of their self‐recovery ability and fatigue resistance, but their relative low mechanical strength and tedious performance adjustment severely limit their applications. Herein, a new strategy to concurrently fabricate hybrid ionic–covalent DN hydrogels and modulate their structures and mechanics is reported, in which an in situ formed chitosan ionic network is incorporated by post‐crosslinking the chitosan‐based composite hydrogel using multivalent anions solutions. The obtained hybrid DN hydrogels exhibit predominant mechanical properties including superior elastic modulus, high tensile strength, and ultrahigh fracture energy because of the more efficient energy dissipation of rigid short‐chain chitosan network. Notably, the swollen hydrogels still remain mechanically strong and tough even after immersion in water for 24 h. More significantly, simply changing the post‐crosslinking time can vary the compactness and rigidity of the chitosan network in situ, achieving flexible and efficient modulation of the structures and mechanics of the hybrid DN hydrogels. This study opens up a new horizon in the preparation and regulation of DN hydrogels for promising applications in tissue scaffolds, actuators, and wearable devices.     

Vitrimer Elastomer‐Based Jigsaw Puzzle‐Like Healable Triboelectric Nanogenerator for Self‐Powered Wearable Electronics

Functional polymers possess outstanding uniqueness in fabricating intelligent devices such as sensors and actuators, but they are rarely used for converting mechanical energy into electric power. Here, a vitrimer based triboelectric nanogenerator (VTENG) is developed by embedding a layer of silver nanowire percolation network in a dynamic disulfide bond‐based vitrimer elastomer. In virtue of covalent dynamic disulfide bonds in the elastomer matrix, a thermal stimulus enables in situ healing if broken, on demand reconfiguration of shape, and assembly of more sophisticated structures of VTENG devices. On rupture or external damage, the structural integrity and conductivity of VTENG are restored under rapid thermal stimulus. The flexible and stretchable VTENG can be scaled up akin to jigsaw puzzles and transformed from 2D to 3D structures. It is demonstrated that this self‐healable and shape‐adaptive VTENG can be utilized for mechanical energy harvesters and self‐powered tactile/pressure sensors with extended lifetime and excellent design flexibility. These results show that the incorporation of organic materials into electronic devices can not only bestow functional properties but also provide new routes for flexible device fabrication.     

Unique Shape Memory Elastomer Associated with Reversible Sacrificial Hydrogen Bonds: Tough and Flexible When below Its Tg

Thermally induced shape memory polymers (SMPs) are fragile and brittle when cooling to a low temperature to generate temporary shapes. In the present study, the authors implement a new design strategy for fabricating elastomeric SMPs with low‐temperature flexibility by engineering reversible sacrificial hydrogen bonds into a chemically crosslinked network. Compatible, amorphous, hindered phenol moieties (Irganox 1010) are incorporated into epoxidized natural rubber (ENR) and the ENR composites are cured with zinc diacrylate (ZDA). Such reversible sacrificial bonds can rupture prior to the rupture of the bonds of the crosslinked network during stretching, which will dissipate energy and facilitate reorientation of the rubber chains. Based on the functional mechanisms, ENR composites exhibit unusual toughness and flexibility and can undergo large deformations even when below their T_g. Irganox 1010 can also be used to tune the glass transition temperature (T_g) and improve the chain mobility of the elastomer sample by providing sufficient intermolecular hydrogen bonding interactions. ENR composites demonstrate thermally triggered shape memory performance. Moreover, the dissociation/reformation of hydrogen bonds upon stretching/cooling can endow the elastomer sample with unique reversible plastics shape memory (RPSM) performance. These SMPs possess excellent shape fixity and recovery.

     

Tough and Water‐Insensitive Self‐Healing Elastomer for Robust Electronic Skin

An electronic (e‐) skin is expected to experience significant wear and tear over time. Therefore, self‐healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e‐skin. However, previously reported elastomers and especially self‐healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch‐insensitive high stretchability (1200%), high toughness of 12 000 J m^?2, and autonomous self‐healing even in artificial sweat. The tough self‐healing materials enable the wafer‐scale fabrication of robust and stretchable self‐healing e‐skin devices, which will provide new directions for future soft robotics and skin prosthetics.     

An Elastic Autonomous Self‐Healing Capacitive Sensor Based on a Dynamic Dual Crosslinked Chemical System

Adopting self‐healing, robust, and stretchable materials is a promising method to enable next‐generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self‐healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self‐healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal‐coordinated bonds (β‐diketone–europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self‐healing and exhibits excellent elasticity. The polymer network forms a microphase‐separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self‐healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self‐healable dielectric layer is fabricated with a dual‐dynamic bonding polymer system and self‐healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self‐healable touch pad.     

Advanced Materials for Use in Soft Self‐Healing Devices

Devices integrated with self‐healing ability can benefit from long‐term use as well as enhanced reliability, maintenance and durability. This progress report reviews the developments in the field of self‐healing polymers/composites and wearable devices thereof. One part of the progress report presents and discusses several aspects of the self‐healing materials chemistry (from non‐covalent to reversible covalent‐based mechanisms), as well as the required main approaches used for functionalizing the composites to enhance their electrical conductivity, magnetic, dielectric, electroactive and/or photoactive properties. The second and complementary part of the progress report links the self‐healing materials with partially or fully self‐healing device technologies, including wearable sensors, supercapacitors, solar cells and fabrics. Some of the strong and weak points in the development of each self‐healing device are clearly highlighted and criticized, respectively. Several ideas regarding further improvement of soft self‐healing devices are proposed.     

Chelation Crosslinking of Biodegradable Elastomers

Widely present in nature and in manufactured goods, elastomers are network polymers typically crosslinked by strong covalent bonds. Elastomers crosslinked by weak bonds usually exhibit more plastic deformation. Here, chelation as a mechanism to produce biodegradable elastomers is reported. Polycondensation of sebacic acid, 1,3-propanediol, and a Schiff-base (2-[[(2-hydroxyphenyl) methylene]amino]-1,3-propanediol) forms a block copolymer that binds several biologically relevant metal ions. Chelation offers a unique advantage unseen in conventional elastomer design because one ligand binds multiple metal ions, yielding bonds of different strengths. Therefore, one polymeric ligand coordinated with different metal ions produces elastomers with vastly different characteristics. Mixing different metal ions in one polymer offers another degree of control on material properties. The density of the ligands in the block copolymer further regulates the mechanical properties. Moreover, a murine model reveals that Fe³⁺ crosslinked foam displays higher compatibility with subcutaneous tissues than the widely used biomaterial—polycaprolactone. The implantation sites restore to their normal architecture with little fibrosis upon degradation of the implants. The versatility of chelation-based design has already shown promise in hydrogels and highly stretchy nondegradable polymers. The biodegradable elastomers reported here would enable new materials and new possibilities in biomedicine and beyond.     

Hierarchical Hydrogen Bonds Directed Multi‐Functional Carbon Nanotube‐Based Supramolecular Hydrogels

Supramolecular hydrogels (SMHs) are three‐dimensional networks filled with a large amount of water. The crosslinking force in the 3D network is always constructed by relatively weak and dynamic non‐covalent interactions, and thus SMHs usually possess extremely high susceptibility to external environment and can show extraordinary stimuli‐responsive, self‐healing or other attractive properties. However, the overall crosslinking force in hydrogel networks is difficult to flexibly modulate, and this leads to limited functions of the SMHs. In this regard, hierarchical hydrogen bonds, that is, the mixture of relatively strong and relatively weak hydrogen bonds, are used herein as crosslinking force for the hydrogel preparation. The ratio of strong and weak hydrogen bonds can be finely tuned to tailor the properties of resultant gels. Thus, by delicate manipulation of the overall crosslinking force in the system, a hydrogel with multiple (thermal, pH and NIR light) responsiveness, autonomous self‐healing property and interesting temperature dependent, reversible adhesion behavior is obtained. This kind of hierarchical hydrogen bond manipulation is proved to be a general method for multiple‐functionality hydrogel preparation, and the resultant material shows potential for a range of applications.     

Self-Healing Polymers Based on Coordination Bonds

Self-healing ability is an important survival feature in nature, with which living beings can spontaneously repair damage when wounded. Inspired by nature, people have designed and synthesized many self-healing materials by encapsulating healing agents or incorporating reversible covalent bonds or noncovalent interactions into a polymer matrix. Among the noncovalent interactions, the coordination bond is demonstrated to be effective for constructing highly efficient self-healing polymers. Moreover, with the presence of functional metal ions or ligands and dynamic metal–ligand bonds, self-healing polymers can show various functions such as dielectrics, luminescence, magnetism, catalysis, stimuli-responsiveness, and shape-memory behavior. Herein, the recent developments and achievements made in the field of self-healing polymers based on coordination bonds are presented. The advantages of coordination bonds in constructing self-healing polymers are highlighted, the various metal–ligand bonds being utilized in self-healing polymers are summarized, and examples of functional self-healing polymers originating from metal–ligand interactions are given. Finally, a perspective is included addressing the promises and challenges for the future development of self-healing polymers based on coordination bonds.     

Cooking‐Inspired Versatile Design of an Ultrastrong and Tough Polysaccharide Hydrogel through Programmed Supramolecular Interactions

Simultaneously achieving strength and toughness in soft materials remains a challenge, especially for physically crosslinked hydrogels with many inactive interaction sites. In this work, inspired by the cooking of thick soup in China, a facile method that includes free water evaporation of the diluted pregel solution followed by crosslinking (WEC) is proposed to fabricate polysaccharide hydrogels. Herein, without the constraints of viscosity and crosslinking, polymer chains can homogenously approach as much as possible, thereby enabling the transformation of inactive supramolecular interaction (H‐bonding and ionic coordination) sites into active sites until reaching the maximum level. Through facilely tuning the concentrating degree, programmed supramolecular interactions, serving as energy‐dissipating sacrificial bonds, impart the hydrogels with strength and toughness over a very wide range, where a “ductile‐to‐tough” transition is discovered to occur first. Using WEC in alginate, the concentration can be as high as 25 wt% without sacrificing processing ability, a result that is significantly beyond common value (3–7 wt%), and the extremely stiff and tough hydrogels are obtained, superior to isotropic alginate hydrogels ever reported. This research offers a facile and versatile strategy to fabricate isotropic polysaccharide hydrogels, which become ideal matrix materials for further fabrication of hybrid or anisotropic hydrogels.     

Simulation‐Experimental Approach to Investigate the Role of Interfaces in Self‐Replenishing Composite Coatings

To investigate self‐replenishing on surface‐structured composite coatings a dual simulation‐experimental approach is employed to study the decisive role of polymer‐air and polymer‐particle interfaces. Experimentally, the composite system consists of a cross‐linked polymer network with fluorinated‐dangling chains, embedding colloidal SiO₂ nanoparticles which are incorporated in the network via covalent bonding. These particles provide the desired surface structure at the air‐interface before and after damage. Any damage replicates the rough surface, while the polymer layer on top of the particles serves as source of low surface energy groups which are able to reorient towards the new air‐interfaces. Using coarse‐grained simulations details of these self‐replenishing composite systems are revealed such as the minimum thickness of the polymer layer necessary for providing optimal self‐replenishing ability and the distribution profile of the dangling chains at the various interfaces. The principles and dual approach reported here may be applied to other self‐healing composite systems with applications in self‐cleaning, anti‐fouling or low adhesion materials.     

本征型自修复高聚物粘结炸药的制备与损伤愈合性能

为减轻高聚物粘结炸药(PBX)由于力、热等环境因素所产生的微裂纹等损伤对于其性能与使用寿命的影响,根据颗粒填充高分子复合材料的结构特性,设计合成了含DA键的本征型自修复高聚物粘结剂,以期实现PBX内部损伤的自主修复。研究结果表明,采用含可逆DA共价键的TAPE-DAPU为粘结剂,设计制备的PBX材料具有较强的损伤愈合能力,当损伤较轻时,该PBX的强度恢复率超过95%,对于较严重的贯穿性损伤,其修复效率也在65%以上。      

Optimal Reactivity and Improved Self‐Healing Capability of Structurally Dynamic Polymers Grafted on Janus Nanoparticles Governed by Chain Stiffness and Spatial Organization

Structurally dynamic polymers are recognized as a key potential to revolutionize technologies ranging from design of self‐healing materials to numerous biomedical applications. Despite intense research in this area, optimizing reactivity and thereby improving self‐healing ability at the most fundamental level pose urgent issue for wider applications of such emerging materials. Here, the authors report the first mechanistic investigation of the fundamental principle for the dependence of reactivity and self‐healing capabilities on the properties inherent to dynamic polymers by combining large‐scale computer simulation, theoretical analysis, and experimental discussion. The results allow to reveal how chain stiffness and spatial organization regulate reactivity of dynamic polymers grafted on Janus nanoparticles and mechanically mediated reaction in their reverse chemistry, and, particularly, identify that semiflexible dynamic polymers possess the optimal reactivity and self‐healing ability. The authors also develop an analytical model of blob theory of polymer chains to complement the simulation results and reveal essential scaling laws for optimal reactivity. The findings offer new insights into the physical mechanism in various systems involving reverse/dynamic chemistry. These studies highlight molecular engineering of polymer architecture and intrinsic property as a versatile strategy in control over the structural responses and functionalities of emerging materials with optimized self‐healing capabilities.     

Self‐Healing Micellar Ion Gels Based on Multiple Hydrogen Bonding

Ion gels, composed of macromolecular networks filled by ionic liquids (ILs), are promising candidate soft solid electrolytes for use in wearable/flexible electronic devices. In this context, the introduction of a self‐healing function would significantly improve the long‐term durability of ion gels subject to mechanical loading. Nevertheless, compared to hydrogels and organogels, the self‐healing of ion gels has barely investigated been because of there being insufficient understanding of the interactions between polymers and ILs. Herein, a new class of supramolecular micellar ion gel composed of a diblock copolymer and a hydrophobic IL, which exhibits self‐healing at room temperature, is presented. The diblock copolymer has an IL‐phobic block and a hydrogen‐bonding block with hydrogen‐bond‐accepting and donating units. By combining the IL and the diblock copolymer, micellar ion gels are prepared in which the IL phobic blocks form a jammed micelle core, whereas coronal chains interact with each other via multiple hydrogen bonds. These hydrogen bonds between the coronal chains in the IL endow the ion gel with a high level of mechanical strength as well as rapid self‐healing at room temperature without the need for any external stimuli such as light or elevated temperatures.     

Mixed Reversible Covalent Crosslink Kinetics Enable Precise,Hierarchical Mechanical Tuning of Hydrogel Networks

Hydrogels play a central role in a number of medical applications and new research aims to engineer their mechanical properties to improve their capacity to mimic the functional dynamics of native tissues. This study shows hierarchical mechanical tuning of hydrogel networks by utilizing mixtures of kinetically distinct reversible covalent crosslinks. A methodology is described to precisely tune stress relaxation in PEG networks formed from mixtures of two different phenylboronic acid derivatives with unique diol complexation rates, 4‐carboxyphenylboronic acid, and o‐aminomethylphenylboronic acid. Gel relaxation time and the mechanical response to dynamic shear are exquisitely controlled by the relative concentrations of the phenylboronic acid derivatives. The differences observed in the crossover frequencies corresponding to pK_a differences in the phenylboronic acid derivatives directly connect the molecular kinetics of the reversible crosslinks to the macroscopic dynamic mechanical behavior. Mechanical tuning by mixing reversible covalent crosslinking kinetics is found to be independent of other attributes of network architecture, such as molecular weight between crosslinks.     

Intrinsic 3D Prestressing: A New Route for Increasing Strength and Improving Toughness of Hybrid Inorganic Biocements

Cement is the most consumed resource and is the most widely used material globally. The ability to extrinsically prestress cementitious materials with tendons usually made from steel allows the creation of high‐strength bridges and floors from this otherwise brittle material. Here, a dual setting cement system based on the combination of hydraulic cement powder with an aqueous silk fibroin solution that intrinsically generates a 3D prestressing during setting, dramatically toughening the cement to the point it can be cut with scissors, is reported. Changes of both ionic concentration and pH during cement setting are shown to create an interpenetrating silk fibroin inorganic composite with the combined properties of the elastic polymer and the rigid cement. These hybrid cements are self‐densifying and show typical ductile fracture behavior when dry and a high elasticity under wet conditions with mechanical properties (bending and compressive strength) nearly an order of magnitude higher than the fibroin‐free cement reference.     

Self‐Healing of Polarizing Films via the Synergy between Gold Nanorods and Vitrimer

Conventional self‐healing is about the recovery of shape and mechanical properties. In contrast, recovery of functional properties is still a great challenge, especially for optical functional materials, as the known self‐healing methods are incompatible with optical properties. By utilizing the synergistic effect between Au nanorods and vitrimer, the alignment of Au nanorods can be achieved in the crosslinked polymer. The optical properties of the resulting polarizing film, such as light transmittance and polarization degree, can be fully recovered without an external repair agent. With simple laser irradiation to induce the photothermal effect of Au nanorods, the shape‐memory effect of vitrimer returns the Au nanorods to their initial orientation, and the plasticity achieves in situ self‐healing of the cutting area. The self‐healing of polarizing film provides a new research direction and reference for the application of self‐healing systems in functional materials.