Self-healing Materials Research Articles

Realization of dual crosslinked network robust, high toughness self-healing polyurethane elastomers for electronics applications

Currently, research into self-healing polyurethane materials has progressed significantly; however, ensuring that the materials exhibit excellent mechanical properties and good healing efficiency is an urgent problem. In this study, a self-healing polyurethane elastomer exhibiting the synergistic enhancement effect of a double-crosslinked network is prepared by introducing a hydrogen-bond functional monomer and the Diels-Alder reaction. Consequently, the resulting elastomer shows a high fracture strength of 72.5 MPa, an elongation at break of 1241.0 %, an ultrahigh toughness of 235.7 MJ/m3, and a fracture energy of 219.4 KJ/m2. Dynamic covalent crosslinking and reversible hydrogen bonding dual networks endow the elastomers with good self-healing properties and multiple repair capabilities, thus allowing them to achieve up to 86 % self-healing efficiency. In addition, we prepare self-healing capacitive electronic devices using a liquid metal blended and compounded with a dual dynamic bonded polymer system, which exhibit stable electrochemical properties, excellent mechanical properties, excellent self-healing properties, and two-component recyclable properties after mechanical training. The self-repairing device can be reused, thus significantly reducing material waste and pollution, and benefits environmental and resource conservation.

New recyclable and self-healing elastomer composites using waste from toner cartridges

Product recycling reintroduces what is discarded as waste and minimizes the environmental impact on our society. Among the different types of waste from electrical and electronic equipment, toner recycling often falls short, downcycling plastic components. This study introduces an innovative approach in which waste parts from toner cartridges are valorized to develop (recyclable and) self-healing elastomeric composite materials. The synergy between carboxylated nitrile rubber (XNBR) as the elastomeric phase and high-impact poly (styrene) (HIPS) as the thermoplastic phase derived from toner cartridge waste was explored and optimized. This combination resulted in the creation of a thermoplastic elastomer exhibiting robust mechanical properties and self-healing capabilities with a tensile strength of 6.6 ± 0.2 MPa and a temperature-driven mechanical recovery of 100%. Furthermore, the capacity of toner powder, an integral component of waste, to act as a reinforcing filler was confirmed, with a 50% increase in mechanical strength compared with the unfilled composite. Moreover, an increase in toner content (up to 20 phr) resulted in an optimal balance between tensile strength and self-healing capacity, surpassing the traditional antagonism between these properties. As a result, this research opens a new pathway in the field of self-healing composites and suggests a practical and environmentally friendly approach for managing electronic waste, effectively supporting the principles of Circular Economy.

Mechanical Robust, Self-Healable Polyurethane Elastomer Enabled by Hierarchical Hydrogen Bonds and Disulfide Bonds.

The fabrication of mechanically robust and self-healing polymeric materials remains a formidable challenge. To address the drawbacks, a core strategy is proposed based on the dynamic hard domains formed by hierarchical hydrogen bonds and disulfide bonds. The dynamic hard domains dissipate considerable stress energy during stretching. Meanwhile, the synergistic effect of hierarchical hydrogen bonds and disulfide bonds greatly enhances the relaxation dynamics of the PU network chains, thus accelerating network reorganization. Therefore, this designed strategy effectively solves the inherent drawback between cohesive energy and relaxation dynamics of the PU network. As a result, the PU elastomer has excellent mechanical properties (9.9 MPa and 44.87 MJ/m3) and high self-healing efficiency (96.2%). This approach provides a universal but valid strategy to fabricate high-performance self-healing polymeric materials. Meanwhile, such materials can be extended to emerging fields such as flexible robotics and wearable electronics.

Modeling and analysis of multi-functional self-healing material using Runge-Kutta Method for investigation of aircraft wing structure

ABSTRACT This paper presents the deployment of Runge-Kutta method to overcome the main challenge in analysis of failure of aircraft wing structure subjected to wind pressure and point loading. Failure phenomenon of any structure is time dependents and is typically referred as dynamic in engineering mechanics and is fairly a complex to investigate. In this context, the dynamic analysis concept has successfully implemented by using computer program in SCILAB software. The numerical technique is adopted as Runge-Kutta fourth order (RK4) method for performing dynamic behaviour of wind structure. The demonstration of failure mode of wing structure is based on function of time. The numerical approach is deemed to provide a detailed description of these phenomena affecting the overall dynamic of failure envelope of wing structure. The parametric study is presented; likewise the effect on failure of wing structure by changing different wind pressure, length and moment, respectively. The wing structure is analytically validated against available literature. Finally, others important failure results obtained from this analysis has discussed in detail.

Self-healing elastomers from supramolecular random copolymers of 4-vinyl pyridine

For the first time hydrogen bonding complexes between poly(4-vinyl pyridine) (P4VP) and its copolymers were employed as a healing concept for building supramolecular materials with self-healability. P4VP and its random copolymers with stearyl acrylate and stearyl methacrylate were first synthesized via UV light-mediated metal-free polymerization using 4-(10H-phenothiazin-10-yl)-N,N-diphenylaniline as organic photocatalyst. Three complexes between the P4VP homopolymer and the obtained copolymers bearing “hairy” side groups with 3,3′-dithiodipropionic acid (DTDP) as a proton donor crosslinker were studied. Owing to the “solvent”-like mantle formed by lowly ordered stearyl side groups, the complex of poly(4-vinyl pyridine-random-stearyl methacrylate) and DTDP exhibited efficient self-healability of complete cuts at room temperature after 30 min, with tensile strength recovery of above 80%. The results of this work suggested that this dynamic supramolecular concept based on P4VP is promising for developing self-healing materials for various applications.

Retaining the specific capacitance under electrochemical stress: A pH-induced self-protection mechanism for manganese dioxide pseudocapacitive electrodes

In this study, we report the enhanced electrochemical performance of a MnO2 electrode modified with a pH-sensitive co-polymer, activated at acidic pH, and designed to counteract MnO2 degradation in aqueous aqueous pseudocapacitors. The conformation of this polymer is controlled by the local pH changes that occur at the electrode/electrolyte interface during electrochemical stress associated to oxygen evolution.As a proof of concept, we demonstrate that the addition of the pH-sensitive polymer contributes to improved electrode integrity and lifetime under over-polarization with oxygen evolution. After undergoing 10 cycles of electrochemical stress, the MnO2/pH-sensitive polymer composite retains ∼ 70 % of its capacitance. This remarkable result stands in stark contrast with the pristine MnO2 electrode which fails catastrophically under the same stress conditions. We believe that this pH-induced self-protection mechanism represents a significant advancement in the development of novel smarter self-healing electroactive materials for the next generation of energy storage devices.

XFEM and machine learning combined approach for failure prediction of microcapsules in cement-based self-healing materials

The cracking behavior of microcapsules in cement-based self-healing materials is essential for releasing healing agents during crack healing. In this study, the extended finite element method and machine learning were combined to predict the competitive behavior of microcapsule debonding and rupture. The fracture criterion based on energy was developed to investigate the interaction of the crack and microcapsule for heterogeneous materials. The artificial neural network was trained on 1031 datasets from extended finite element method (XFEM) simulations, and the mean square error (MSE) was 3.7E-3 and the overall R2 was 0.94 in 16 epochs. With the proposed model, the cracking behavior of microcapsules can be judged accurately and instantly without extensive computation, which can help clarify the release condition of healing agents encapsulated in microcapsules so as to guide the design of intelligent composite materials.

Smart materials: The next generation in science and engineering

In recent years, fascinating developments in various areas of materials science have happened. Smart materials, also known as intelligent or stimuli-responsive materials, have attracted attention in science and engineering. Smart materials are divided into six different groups: shape memory materials, piezoelectric materials, magnetostrictive materials, electro-rheological and magneto-rheological fluids, and self-healing materials. Shape-memory and self-healing materials are the most popular and important kinds of smart materials. Shape-memory materials have the ability to react to certain stimuli, such as temperature, pH, light, magnetic fields, and electric fields, and transform from a temporary shape to their original shape after exposure to these stimuli. Shape-memory alloys and shape-memory polymers have attracted the most attention and are widely used among all kinds of shape-memory materials developed. The two most important properties of shape-memory alloys are shape memory and superelasticity. Shape-memory polymers are gaining popularity because of specific benefits such as their high shape recovery rate, light weight, low density, high strength-to-weight ratio, high shape deformability, and readily tailorable glass transition temperature. Self-healing materials have the ability to fully or partially repair their features and functionality after repeated damage. Self-healing materials are divided into two categories: intrinsic and extrinsic, as well as autonomous and non-autonomous. These materials have the potential to increase their lifetime while reducing maintenance costs. Smart materials have a wide range of applications, including aerospace, automotive, biomedicine, and construction. The goal of this paper is to provide an overview of smart materials.

Material basis and development prospects of nano-flexible sensors

The combination of nanosensors and flexible sensors gives modern sensors an important adaptive capability. Nanomaterials such as nanocellulose and carbon nanotubes have been successfully used for flexible sensors. Nanocellulose can be used as a good fibrous backbone or as a thin film. The nitrocellulose skeleton can be filled with conductive substances, and if the external losses are high, self-healing materials can be added appropriately. Carbon nanotubes have excellent electrical conductivity and performance stability, but also have certain characteristics of flexible and active materials, which can effectively improve the corresponding range and response sensitivity of flexible sensors. The correct use of these materials in the process can also reduce the use of the sensor loss. In this paper, the principle of nano-flexible sensors and the analysis of current products are illustrated by examples. And by analyzing successful experiments or showing the results of current applications of nanomaterials in flexible sensors. This paper focuses on how nanomaterials can be successfully applied to flexible sensors.

Mechanisms boosting material embodied intelligence to realize self-healing soft robots

The recent introduction of self-healing soft materials in robotics is a major step towards sustainable next generation robots. By manufacturing soft robots out of these smart materials, we integrate a self-healing ability and increase the physical intelligence of these systems. However, the embodied intelligence in the material level needs to be augmented by incorporating assistive mechanisms in the system level with minimized control, enabling healing of damage in different sizes and in diverse working conditions. These assistive mechanisms can provide damage detection, damage closure, healing stimuli providing, health monitoring, or a combination of the previous. In this paper, we present two different mechanisms for an autonomous healing of damages; (i) Embedding a healable heater in a self-healing soft actuator to increase the temperature required for an efficient healing, while it allows detecting the damage and monitoring the health of the system. (ii) Incorporating shape memory alloy wires in a self-heling soft bending actuator, with simultaneous sealing through contraction and heating abilities. Apart from assisting in the healing action, both mechanisms play a part in the actuation of the bending robots as strain limiting elements. These assistive mechanisms will overcome the limitation on the material level, leading to robots that can self-heal in applications outside of laboratories and factories.

Molecular design on dual stimuli-responsive azobenzene-containing ionic complexes toward self-healing materials under photoirradiation or humid condition at room temperature

Self-healing materials working at room temperature are attractive in the field of materials chemistry. Compared to those requiring one specific external stimulus, one smart material that can launch the self-healing process under multiple stimuli would accommodate more various working conditions. In this work, a double-chain azobenzene-containing surfactant AZO with good molecular flexibility and hydrophilicity is designed for developing self-healing materials with dual responses to light and humidity. By mixing AZO and surfactants containing linear aliphatic chains, the resulted composites gain crystal-to-isotropic liquid phase change ability under the trigger of either light or humidity, thanks to the formation of sufficient free volume for AZO molecules. This leads to the light-/humidity-induced self-healing materials at room temperature. Meanwhile, the composite of AZO and double-chain surfactant has been proved with better responsive sensitivity to light and humidity by forming a homogeneous molecular distribution. This study provides a new designing strategy for gaining dual self-healing materials working via an athermal way, promoting the development of smart materials with multiple stimuli-responsive property.

Effect of a harsh circular environment on self-healing microbial-induced calcium carbonate materials for preventing Pb2+ migration

Microbially induced carbonate precipitation (MICP) is increasingly being explored for Pb-contaminated water bodies and soil remediation. However, the Pb-related precipitate resulting from the MICP process can possibly leach acid over time when subjected to harsh environments, causing serious threats to human health. In this study, for the first time, self-healing microbial-induced calcium carbonate (MICC) materials are proposed and applied to prevent Pb2+ migration where the Pb-related precipitate is acid leached after spore germination, spore-vegetative cell transformation, urease secretion, and urea hydrolysis, thereby producing spore-containing precipitation. This process was repeated five times to explore the effect of a harsh circular environment on self-healing MICC materials. Results indicated that Pb immobilization would have deteriorated if the inosine and trace elements had not been intervened during spore germination and spore-vegetative cell transformation, respectively. The spores and vegetative cells provided extra nucleation sites for Pb2+ and minerals to attach. The extracellular polymeric substances (EPSs) combined Pb2+ with functional groups and chemical bonds to prevent their migration to surrounding environments. The scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) images also indicated that the cerussite mineral was precipitated prior to the calcite mineral because Pb2+ had more affinity to combine with CO32- and OH-. An immobilization efficiency of greater than 95% remained nearly the same after five cycles, while it reduced very quickly to less than 10% after three cycles when neglecting the self-healing MICC materials, thus highlighting their relative merits.

Self-Healing Antimicrobial Silicones-Mechanisms and Applications.

Organosilicon polymers (silicones) are an important part of material chemistry and a well-established commercial product segment with a wide range of applications. Silicones are of enduring interest due to their unique properties and utility. Recently, new application areas for silicone-based materials have emerged, such as stretchable electronics, wearable stress sensors, smart coatings, and soft robotics. For this reason, research interest over the past decade has been directed towards new methods of crosslinking and increasing the mechanical strength of polyorganosiloxanes. The introduction of self-healing mechanisms may be a promising alternative for such high-value materials. This approach has gained both growing research interest and a rapidly expanding range of applications. Inherent extrinsic and intrinsic self-healing methods have been used in the self-healing of silicones and have resulted in significant advances in polymer composites and coatings, including multicomponent systems. In this review, we present a summary of research work dedicated to the synthesis and applications of self-healing hybrid materials containing polysiloxane segments, with a focus on antimicrobial and antifouling coatings.

Preparation and electrochemical performance study of a self-healing electrode composite material with WSe2/liquid metal Galinstan for lithium-ion batteries

In this work, a room temperature liquid metal alloy (Galinstan) and tungsten diselenide (WSe2) composite anode (LMx@WSe2) were synthesized utilizing a one-step hydrothermal method. Through a comprehensive characterization process, including XRD, SEM, HRTEM, Raman spectroscopy, XPS, and BET, the structural and morphological properties of the synthesized composites were extensively explored. The liquid metal alloy was observed to combine effectively with WSe2 via electrostatic adsorption, coordination, and additional bonding methods. Furthermore, it displayed high fluidity, deformability, and chemical stability. Consequently, the alloy promoted the repair of cracked surface areas in the electrode material and reduced internal oxidation-reduction reactions, leading to improved electrochemical performance during repeated lithium-ion insertion and extraction cycles. After 500 cycles at a current density of 1 A g−1, this composite electrode retained a capacity of 224.5 mAh g−1. Impressively, at a low temperature of − 10 °C, it maintained a capacity of 290 mAh g−1 after 50 cycles at a current density of 0.2 A g−1. Our research may open avenues for addressing mechanical difficulties experienced in flexible electronic devices and self-healing electronic circuits exposed to chemical reaction processes.

An antibacterial, highly stretched and self-healing polyurethane elastomer for flexible electronic devices

Broadening the range of practical applications of self-healing materials has become a research hotspot for the development of durable and smart materials. This study the development of a hydrogen bond-rich of self-healing elastomer, formed by the combination of disulfide and diazolidinyl urea (DU) cross-linked polyurethane polymers (PDD). The prepared polyurethane elastomer material possessed extremely high mechanical properties (including a stress of 25 MPa and high toughness of 306 MJ/m3). Besides, PDD exhibited an excellent self-healing performance. Even if it is subjected to long-term tensile deformation or extreme strain, it could recover almost completely to its initial state within 12 h in a 60 °C environment. In addition, the synergistic effect of diazolidinylurea and element S on the polymer film gave the material excellent antimicrobial properties. Finally, we added carbon nanotubes into the polyurethane system and assembled them into smart sensors for applications in flexible electronic devices. The versatility of this sensor has been demonstrated in human motion applications.

Self-healing and malleable waterborne polyurethane bearing aliphatic disulfide linkages with hydrophobic branching chains

Self-healing polymers have attracted extensively interests to improving durability of materials. A promising strategy to prepare self-healing materials is the incorporation of dynamic disulfide bonds into polymer backbones. In this study, a novel hydrophobic chain extender containing disulfide bond (CY-OA) has been successfully synthesized and used to elevate the practical application capability of the self-healing WPU. FT-IR and Raman spectra confirmed that the disulfide bonds were successfully incorporated into the polyurethane backbones. The synthetic self-healing waterborne polyurethanes (SHWPUs) all had the high-water contact angle above 108° and the low water absorption below 5%, exhibiting the good hydrophobicity and water resistance. Increasing addition of CY-OA simultaneously optimized the mechanical properties and self-healing efficiency of SHWPUs. The mechanical properties of repaired SHWPU-4 film had been almost recovered to its original values (tensile strength and elongation at break were 12.79 MPa and 1003%) at 120 °C for 1 h. Meanwhile, the feature of dynamic disulfide bonds produced a relatively low activation energy of 54.78 kJ/mol, resulting in a good self-healing efficiency of 93%. Therefore, this hydrophobic self-healing WPU contributed the scratch resistance, water resistance, reprocess ability and further got the feasibility of practical applications.

Ultrarobust self-healing elastomers with hydrogen bonding connected MXene network for actuator applications

Self-healing ability is highly desired for flexible actuators that operate in dynamic and real-world environments, as these machines are vulnerable to mechanical damage. However, self-healing properties and mechanical strength are often difficult to combine at the same time. We report a synergistic enhancement strategy based on the ordered micro-nano structure and interfacial hydrogen bonding aggregation to achieve self-healing elastomer toughening. The hydrogen bonding interaction drives the MXene nanosheet to self-assemble into an interconnected network around the PU latex microsphere. Thanks to the synergy of dynamic physical networks and high-density interfacial hydrogen bonding, the composites with controllable room temperature self-healing efficiency (76.5–95.9%) and tensile strength (17.7–42.6 MPa). Furthermore, the MXene network structure of the composite endows the actuator with an efficient photothermal conversion efficiency, fast responsiveness, and even functional recovery. It is an effective strategy to achieve high-strength self-healing materials through hydrogen bonding connected MXene network and interfacial hydrogen bonding aggregation, which is expected to be applied to other flexible devices, such as flexible sensors and electromagnetic shielding.

Self-healing luminescent polyurethane with ultrahigh toughness resulting from lanthanide-bipyridine segment and hydrogen bonds

Synthesis and manufacturing a new generation of luminescent elastomers that simultaneously features self-healing efficiency with superior mechanical properties remains a challenge due to the compromise between toughness and self-healing ability. Here, a new class of transparent luminescent materials was synthesized via coordinating lanthanide (Ln3+) to bipyridine (Bpy) units introduced into the polymer backbone prepared by polymerization of Polytetramethylene ether glycol (PTMEG) and 4-methylenedicyclohexyl diisocyanate (HMDI). Relying on collaborative reinforcement of a great number of loosely packed Ln3+-ligand coordination bonds and hydrogen bonds (H-bonds), the prepared luminescent polymers showed an ultrahigh toughness of 373.12 MJ m−3 and a mechanical ultrahigh strength of 33.73 MPa. In addition, the multi-color emission behavior of the luminescent materials can be simply adjusted via tailoring the molar ratio of Eu3+/Tb3+. The luminescent self-healing materials can reversibly respond to acid-base vapor because of protonation/deprotonation of Bpy ligands. We believe luminescent polymers obtained by us with excellent mechanical properties and luminescence off/on switching ability show great potential applications as acid-base detector.

An enhanced lattice beam element model for the numerical simulation of rate-dependent self-healing in cementitious materials

This paper describes the development of a discrete lattice model for simulating structures formed from self-healing cementitious materials. In particular, a new approach is presented for simulating time dependent mechanical healing in lattice elements. The proposed formulation is designed to simulate the transient damage and healing behaviour of structures under a range of loading conditions. In addition, multiple and overlapping damage and healing events are considered. An illustrative example demonstrates the effects of varying the healing agent curing parameters on the computed mechanical response. The model is successfully validated using published experimental data from two series of tests on structural elements with an embedded autonomic self-healing system. The meso-scale model gives detailed information on the size and disposition of cracking and healing zones throughout an analysis time history. The model also provides an accurate means of determining the volume of healing agent required to achieve healing for all locations within a structural element. The importance of the information provided by the model for the design of self-healing cementitious material elements is highlighted.

Development of a Robust Self-Healing Biomass Composite Gel Material for Spontaneous Combustion Prevention in Coal Mines

Development of a Robust Self-Healing Biomass Composite Gel Material for Spontaneous Combustion Prevention in Coal Mines