High Self-healing Efficiency Research Articles

Design and synthesis of UV-cured calixarene polyurethane coatings: balancing robust mechanical properties with high self-healing efficiency

Design and synthesis of UV-cured calixarene polyurethane coatings: balancing robust mechanical properties with high self-healing efficiency

Robust self-healing capacity and high mechanical properties of castor oil-based waterborne polyurethane based on “kill two birds with one stone” strategy

Achieving ideal combination of high self-healing efficiency and good mechanical properties is of significance for the breakthrough in the application of self-healing materials. Herein, the functionalized castor oil-based waterborne polyurethane (DA-CWPU) was constructed based on “killing two birds with one stone” molecular design strategy with the addition of self-healing monomer D-A adduct. Firstly, D-A adduct containing flexible D-A bonds and rigid ring structure was prepared by D-A reaction with furfuryl alcohol (FA) and bismaleimide (BMI) as raw materials, which could not only effectively enhanced the self-healing ability of the material, but also ensured the strong mechanical properties. Then, DA-CWPU emulsion with favourable self-healing and mechanical properties was synthesized by the polymerization of castor oil (CO), isophorone diisocyanate (IPDI) and D-A adduct. The DA-CWPU film has preferable self-healing efficiency (93 % at 100 °C for 50 min), unique shape memory effect (rehabilitate after heating at 100 °C for 45 s), good toughness (485 MJ/m3), strong tensile strength (5.96 MPa) and sufficient elongation (115 %). At the same time, the self-healing DA-CWPU film can be recycled through solution casting. The sustainable castor oil-based waterborne polyurethane can be used as finishing agents for leather products, which realizes repeatedly self-healing in case of surface damage, greatly increasing the service life of the material and mechanical properties, providing a new approach for the development of mechanically robust self-healing materials.

Effect of lubricant loading in slippery liquid-infused surface for persistent anti-icing performance

Due to the vast applications in biomedical materials and aerospace industry, smart slippery liquid-infused porous surfaces (SLIPSs) have attracted remarkable attention. However, there are still challenges in the fabrication of durable SLIPS. In this work, based on linear polyurea and silicone oil, a series of durable anti-icing surface were fabricated. Based on the long-lasting secretion of lubricant, the ice adhesion strength of 60-PUa was 2.7 ± 0.5 kPa and could remain below 10 kPa even after 30 icing-deicing cycles. And the icing delay time of 60-PUa could be extended up to 870 s at a temperature of −15 °C. The introduction of large numbers of reversible hydrogen bonds in the system and silicone oil made it possible to achieve high self-healing efficiency under natural conditions. The coating system not only improved the ice removal ability, but also had excellent water-sliding properties, the droplet could slide under its own weight on 60-PUa at a tilt angle of 4.7°. This work provides an easy way to fabricate multi-functional SLIPS with durability.

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.

Biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor based on liquid metal-polydimethylsiloxane elastomer

Flexible strain sensors (FSS) have garnered widespread attention due to their immense potential in wearable electronics, motion health monitoring, artificial electronic skin, and soft robotics. However, FSSs are susceptible to mechanical damage such as wear, cracks or breaks during long-term use, which diminish their reliability and service life. Inspired by the self-healing dual-phase structure of human skin and vascular networks, this study proposes a biomimetic three-dimensional microchannel non-destructive self-healing flexible strain sensor (B-TMN-SHFSS) based on the liquid metal-polydimethylsiloxane (LM-PDMS) elastomer. The B-TMN-SHFSS employs a layered design, layer-by-layer fabrication, and interlayer self-healing techniques to construct the microchannel within the self-healing PDMS elastomer (SPE), with the liquid metal (LM) being injected into the microchannel using a negative pressure injection method. Based on the modified protective layer design of the biomimetic three-dimensional microchannel, the high self-healing efficiency of the SPE and the fluidity of the LM, the B-TMN-SHFSS is able to restore the initial sensing performance after self-healing, while maintaining the integrity of the 3D microchannels with an electrical healing efficiency (EHE) of 100 %. Additionally, the B-TMN-SHFSS features high sensitivity (GFmax = 3.464) and a wide measurement range (0 to 216.68 %), making it suitable for human motion detection.

Bio-based polyurethane vitrimer with imine bonds: Excellent thermo-mechanical properties and heat recovery

Preparation of vitrimer with excellent performance from biomass feedstock can effectively reduce the waste of fossil fuels and the pollution problem to the environment. In this paper, vanillin (VAN) and 4-amino-3-methylphenol, which are biobased raw materials, were used to prepare the imine-bonded diol AMV-OH in a one-step process, which was incorporated into the main chain of vitrimer polymer, and a series of imine-bonded vitrimer materials AMV-V was obtained by using pentaerythritol tetra-3-mercaptopropionate (PETMP) as a cross-linking agent. The mechanical property analysis, solvent resistance analysis, DSC thermal analysis, DMA analysis and self-repair characterization showed that AMV-V exhibited good thermo-mechanical properties (the highest initial degradation temperature was 246 °C with a Tg value of 17 °C). The results showed that specific mechanical properties could be obtained by adjusting the contents of PETMP and AMV-OH, among which the best tensile properties were obtained at 10 mmol of AMV-OH, with a tensile strength of 8.03 MPa and an elongation at break of 316.79 %. Meanwhile, the AMV-V samples were able to achieve self-healing properties under milder conditions (100 °C, 10 MPa repair for 1 h) and had a high self-healing efficiency (H=94.80 %, R=83.72 %).

Self-Healing Polyurethane Elastomers with Superior Tensile Strength and Elastic Recovery Based on Dynamic Oxime-Carbamate and Hydrogen Bond Interactions.

The preparation of self-healing polyurethane elastomers (PUEs) incorporating dynamic bonds is of considerable practical significance. However, developing a PUE with outstanding mechanical properties and high self-healing efficiency poses a significant challenge. Herein, this work has successfully developed a series of self-healing PUEs with various outstanding properties through rational molecular design. These PUEs incorporate m-xylylene diisocyanate and reversible dimethylglyoxime as hard segment, along with polytetramethylene ether glycol as soft segment. A significant amount of dynamic oxime-carbamate and hydrogen bonds are formed in hard segment. The microphase separated structure of the PUEs enables them to be colorless with a transparency of >90%. Owing to the chemical composition and multiple dynamic interactions, the PUEs are endowed with ultra-high tensile strength of 34.5MPa, satisfactory toughness of 53.9MJ m-3, and great elastic recovery both at low and high strains. The movement of polymer molecular chains and the dynamic reversible interactions render a self-healing efficiency of 101% at 70°C. In addition, this self-healing polyurethane could still maintain high mechanical properties after recycling. This study provides a design strategy for the preparation of a comprehensive polyurethane with superior overall performance, which holds wide application prospects in the fields of flexible displays and solar cells.

A reusable, healable, and biocompatible PEDOT:PSS hydrogel-based electrical bioadhesive interface for high-resolution electromyography monitoring and time–frequency analysis

As the most ideal interface between bioelectronic devices and biological tissues, the electrical bioadhesive interface (EBI) holds significant potential for various applications, including soft bioelectronics, wearable devices, and electrophysiological signal monitoring. However, most current EBIs are disposable products that lack repeatable adhesion and self-healing properties, thus hindering practical applications. Herein, we develop a reusable EBI by incorporating a dynamic non-covalent interaction enhancer polydopamine (PDA) and conductive PEDOT:PSS into an adhesive hydrogel matrix polyacrylamide (PAM). The EBI exhibits intriguing overall electrical and mechanical properties, including high conductivity (5.57 S m−1), tissue-like Young’s modulus (2.7 kPa), low interfacial impedance (1 kΩ), and excellent adhesion strength (46.45 ± 1.75 kPa on porcine skin) with excellent retention (87 %) after 200 adhering/detaching cycles, high self-healing efficiency of 94.11 %, and outstanding biocompatibility in HDF-a and HaCaT cell models. Benefiting from these superior properties, we further demonstrate the fabrication and application of an EBI-based reusable electromyography monitoring patch (EMP). The reusable EMP enables high-resolution electromyography signal monitoring capability with a higher signal-to-noise ratio (SNR) of 30.05 dB than commercial electrodes (12.06 dB). Remarkably, such reusable EMP maintains very stable SNR of 21.82 dB after 200 adhering/detaching cycles (3.8 times higher than commercial electrodes, 5.74 dB after 30 cycles), and showcases typical time and frequency-domain characteristics. These findings demonstrate a promising reusable EMP to enhance the accuracy and convenience of electromyography monitoring.

Silver sulfide anchored bismuth molybdate p-n heterojunction nano-coating with excellent photo-thermal self-healing performance

In this research, a self-healing nano-coating with excellent photo-thermal response to near-infrared (NIR) laser is prepared. This coating incorporates silver sulfide anchored bismuth molybdate (Ag2S@Bi2MoO6) into a shape memory epoxy resin to achieve for a good photo-thermal conversion capability. The Ag2S@Bi2MoO6 p-n heterojunction could photo-generate more electron-holes pairs under the NIR laser irradiation. Also, it shows a wider absorption range of visible light, leading to effectively absorb the light energy, generate enough heat to induce the shape memory recovery in the coating, and seal the scratch. The results indicate that the temperature of EP-1 % Ag2S@Bi2MoO6 coating has reached about 88 °C, while good self-healing and anti-corrosion properties with a self-healing rate of 88.41 % have been achieved. Furthermore, calculations based on Density Functional Theory and Finite Element Method pointed out that the formation of p-n heterojunction effectively has enhanced the photo-thermal effect. This research opens a new way for developing self-healing coatings with an ultra-fast response time and high self-healing efficiency.

Co-ordinated polyhedral oligomeric silsesquioxane and cyclodextrin on polyurethane elastomer with network topology for simultaneously improved fatigue-resistant and self-healable properties

Long-term usage can induce cracks on the surface or inside the polyurethane (PU) and cause fatigue damage, thus reducing the performance and lifetime of PU. It is therefore of great practical importance to impart fatigue resistance and self-healing ability to PU. However, the conventional covalent cross-linked network design with irreversible and rigid properties limits their fatigue resistance. Here, we have designed a highly ductile, fatigue-resistant and self-healing PU enabled by the synergistic effect of covalent network topology, dynamic reversible disulfide bonds and multiple hydrogen bond stacking. This judicious design yields excellent mechanical properties such as high tensile strength (7.38 MPa), high elongation at break (1159%) and high toughness (42.91 MJ·m−3). Notably, the PU successfully combines fatigue resistance with self-healing behavior. During 1000 cycles of stretch-release processes at 100% strain, the stress retention of the PU almost unchanged. Moreover, the PU achieves a high self-healing efficiency of 98% after self-healing at 80 ℃ for 2 h. The above-mentioned superiority enables the PU-based strain sensors to have a timely and stable output signal as well as excellent self-healing performance. Such a judicious strategy will facilitate the practical application of durable flexible electronics.

Autonomous self-healing and superior tough polyurethane elastomers enabled by strong and highly dynamic hard domains.

Self-healing materials show exceptional application potential for their high stability and longevity. However, a great challenge of the application of self-healing materials is the tradeoff between mechanical robustness and room temperature self-healing. In order to address this tradeoff, inspired by the characteristic that small molecules of living organisms self-assemble into large protein molecules by non-covalent interactions, we constructed polyurethane with highly dynamic and strong hard domains composed of dense hydrogen bonds and π-π interactions between the phenylurea groups at the end of the side chain. The prepared elastomer (PU-HU2-60) exhibits exceptional tensile performance (tensile strength is 18.27 MPa and ultimate elongation is 904.6%) and crack tolerance (fracture energy is 57.78 kJ m-2), surpassing those of most room temperature self-healing materials. After being damaged, the dynamic change process of hydrogen bonds and π-π interactions enables the elastomer to show a high self-healing efficiency of 92.15% at room temperature. Using molecular dynamics (MD) simulations and experiments, we verified that hydrogen bonds and π-π interactions promote the formation of hard domains and the autonomous self-healing of elastomers. The prepared elastomers can also be recycled and they showed ultra-high and restorable adhesion between metals. This work demonstrates a new strategy to balance the mechanical and self-healing properties of elastomers to expand their practical applications such as metal adhesives.

Self-Powered and Self-Healable Extraocular-Muscle-Like Actuator Based on Dielectric Elastomer Actuator and Triboelectric Nanogenerator.

Although dielectric elastomer actuators (DEAs) are promising artificial muscles for use as visual prostheses in patients with oculomotor nerve palsy (ONP), high driving voltage coupled with vulnerable compliant electrodes limits their safe long-term service. Herein, a self-healable polydimethylsiloxane compliant electrode based on reversible imine bonds and hydrogen bonds is prepared and coated on an acrylic ester film to develop a self-healable DEA (SDEA), followed by actuation with a high-output triboelectric nanogenerator (TENG) to construct a self-powered DEA (TENG-SDEA). Under 135.9kVmm-1 , the SDEA exhibits an elevated actuated strain of 50.6%, comparable to the actuation under DC power. Moreover, the mechanically damaged TENG-SDEA displays a self-healing efficiency of over 90% for 10 cycles. The TENG ensures the safe using of TENG-SDEAs and an extraocular-muscle-like actuator with oriented motion ability integrated by several TENG-SDEAs is constructed. Additionally, the SDEA is directly used as a flexible capacitive sensor for real-time monitoring of the patient's muscle movement. Accordingly, a medical aid system based on a conjunction of the extraocular-muscle-like actuator and a flexible capacitive sensor is manufactured to help the patients suffering from ONP with physical rehabilitation and treatment.

Highly Self-Healable Polymeric Coating Materials Based on Charge Transfer Complex Interactions with Outstanding Weatherability.

In this study, we prepare highly self-healable polymeric coating materials using charge transfer complex (CTC) interactions. The resulting coating materials demonstrate outstanding thermal stability (1 wt% loss thermal decomposition temperature at 420 °C), rapid self-healing kinetics (in 5 min), and high self-healing efficiency (over 99%), which is facilitated by CTC-induced multiple interactions between the polymeric chains. In addition, these materials exhibit excellent optical properties, including transmittance over 91% and yellow index (YI) below 2, and show enhanced weatherability with a ΔYI value below 0.5 after exposure to UV light for 72 h. Furthermore, the self-healable coating materials developed in this study show outstanding mechanical properties by overcoming the limitations of conventional self-healing materials.

Efficient solar-thermal conversion and thermal energy storage towards personal thermal management and thermoelectric power generation enabled by massive screen printing of carbon nanotube dopped energy storage gels

Converting clean solar energy into thermal and electrical energy can effectively alleviate energy shortages and environmental crises. However, the intermittency and low utilization of solar energy are currently urgent issues that need to be addressed. The combination of solar-thermal conversion, heat energy storage, and heat energy utilization has been exploited as an emerging methodology of solar energy utilization. Herein, high-performance solar-harvesting energy storage gels composed of light-absorbing carbon nanotubes, a heat storage medium of an octadecanoic and flexible matrix of SEBS are fabricated by massive screen printing on textiles. The solar absorbance and solar-thermal conversion efficiency of the energy storage gel reach high levels of 96.4 % and 94.8 %, respectively. The printable textiles demonstrate an ultra-high latent heat of 71.12 Jg−1 to enable the large heat storage capacity. The high self-healing efficiency of 92 % ensures its reuse after damage. Due to its efficient photothermal conversion ability and high heat storage capacity, the stored heat can be used for effective thermal compression, providing heat for the human body, and also for thermoelectric conversion. The carbon nanotube dopped energy storage gels provide a state-of-the-art solar-thermal conversion device for the next generation of personal thermal management and thermoelectric power generation.

Room-temperature self-healing polyurethane elastomers with high strength and superior self-healing efficiency based on aromatic disulfide-induced

Polymers are inevitably subject to mechanical damages during molding, processing, and application. Self-healing of internal and surface damage in polymers can be achieved by endowing the materials with room-temperature self-healing functions. This improvement significantly eliminates safety risks caused by material damage, enhances the safety, stability, and service life of polymer materials, facilitates the realization of sustainable resource development, and aligns with the concept of "low carbon". Room-temperature self-healing materials mainly rely on motility of molecular chain segments and dynamical equilibration of forces acting within the system. However, there have been few reports of polyurethane elastomers with high strength and high self-healing efficiency. In this paper, PUIPBD polyurethane elastomers were prepared by the chemical reacting of polytetrahydrofurandiol PTMEG-2000, isophorone diisocyanate IPDI, 1,4-butanediol (BDO) with 4,4′-dihydroxydiphenyl disulfide (DHDDS) as monomers. It was found that the self-healing efficiency of the synthesized polyurethane elastomer series was very high after 48 h of self-healing at 25 °C, all of which exceeded 79 %, and the tensile strength, elongation and fracture toughness of best performing elastomer PU90/10 could reach 89.8 %, 99.9 %, and 95.6 %, respectively after 48 h of self-heal at room temperature, showing good simultaneous room temperature self-healing efficiency.

Environment Endurable, Self-Healing, Super-Adhesive, and Mechanically Strong Ionogels for Reliable Sensing.

Ionogels possess high conductivity, stretchability, and adhesion, making them promising as flexible sensors. However, it remains challenging to fabricate an ionogel which integrates excellent environment endurance, superior mechanical strength, high self-healing efficiency, and super adhesion. Herein, a supramolecular ionic liquid is synthesized using calcium chloride and 1-butyl-3-methylimidazolium chloride. An advanced ionogel based on this supramolecular ionic liquid is conveniently constructed by a one-pot method with acrylamide and acrylic acid as monomers. The supramolecular cross-linking network, formed by affluent coordination interactions, hydrogen bonds, and electrostatic interactions, provides the ionogel with ideal mechanical strength (tensile strength up to 1.7MPa), high self-healing efficiency (up to 149%), super adhesion (up to 358kPa on aluminum), excellent solvent tolerance (less than 10% weight increase, high mechanical and sensing performance retention after being soaked in organic solvents), and low-temperature endurance (breaking elongation can reach 87% at -30 °C). The supramolecular ionogels can function as multi-mode sensors, capable of monitoring strain and different amplitudes of human movements in real-time. Moreover, the sensing performance of ionogels remains unaffected even after being self-healed or exposure to organic solvents. It is expected that this study could offer valuable design ideas to construct advanced gel materials applicable in complicated environment.

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.

Guar Gum-based multifunctional hydrogels with high sensitivity and negligible hysteresis for wearable electronics

As a classic flexible material, hydrogel shows great potential in wearable electronics. However, it remains a challenge to prepare hydrogels that simultaneously have robust toughness, strong mechanical properties, high conductivity, fit to human skin, and strain sensitivity. In this work, oxidized guar gum (OGG) and acrylamide (AM) were used to create a novel hydrogel that is highly strain-sensitive. The hydrogel reveals a skin-like elastic modulus (∼ 29 kPa), high toughness (732.3 kJ·m−3), high breaking elongation (1060%), high adhesion, high self-healing efficiency (96%), and negligible lag (η = 3.9%, energy loss coefficient). Meanwhile, it has good biocompatibility and outstanding antimicrobial qualities. In addition, the introduction of iron ions may increase the conductivity (1.1 S·m−1) while maintaining high transparency, and the gel-based sensor exhibits high sensitivity (GF=11.82). The highly sensitive sensors exhibit very fast response time (55–60 ms) and adequate stability (2000 cycles). Interestingly, hydrogel sensors can monitor a variety of human movements, including large-scale joint bending and tiny facial expressions, gesture recognition and handwriting. In addition, it has been successfully used to transmit encrypted information, human-machine interaction and wireless sensing.

Multiple hydrogen bonds network enabled sustainable and reproducible cellulose/liquid metal composite elastomer for clean energy collection and conversion

Fabrication of sustainable, mechanically robustness and reproducible metal polymer composite elastomer is desirable but remains a challenge. Herein, a multiple hydrogen bonds crosslinked metal polymer composite elastomer derived from cellulose, plant oil, nature rubber and liquid metal was prepared, which exhibited excellent mechanical elasticity, reproducible and photothermal conversion performance. To fabricate the proposed composite elastomer, the liquid metal (LM) droplets were dispersed within a mixture of amino cellulose (AC), pimelic acid modified epoxy soybean oil (ESOPA) and nature rubber matrix through high-frequency ultrasonication. The active groups of the AC and ESOPA were able to not only construct a multiple hydrogen bonds network to endow the composite elastomer with excellent mechanical strength (1.51 MPa) and stretchability (515.3%), but also stabilize the LM particles. And the broken and reconstruction of the multiple hydrogen bonds network allowed the composite elastomer to be healed quickly at room temperature with high self-healing efficiency of 97.28%. In addition, the LM in the waste composite elastomers could be effectively recycled through dissolution and extraction as well as obtained a regenerative NR/ESOPA/AC elastomer, and the recycling efficiency of LM was up to 85%. Most importantly, the NR/ESOPA/AC/LM composite elastomer possessed stable photothermal conversion property, and has been successfully applied to convert light energy to thermal, electric and kinetic energy to drive the Stirling motor and electric fan, which paved a promising strategy for clean energy collection and conversion.

Asymmetric Hard Domain-Induced Robust Resilient Biocompatible Self-Healable Waterborne Polyurethane for Biomedical Applications.

The synthesis of eco-friendly and biocompatible waterborne polyurethanes (WPUs) through judicious molecular engineering with supreme mechanical strength, good shape recoverability, and high self-healing efficiency is still a formidable challenge because of some mutually exclusive conflicts among these properties. Herein, we report a facile method to develop a transparent (80.57-91.48%), self-healable (efficiency 67-76%) WPU elastomer (strain 3297-6356%) with the highest reported mechanical toughness (436.1 MJ m-3), ultrahigh fracture energy (126.54 kJ m-2), and good shape recovery (95% within 40 s at 70 °C in water). These results were accomplished by introducing high-density hindered urea-based hydrogen bonds, an asymmetric alicyclic architecture (isophorone diisocyanate-isophorone diamine), and the glycerol ester of citric acid (a bio-based internal emulsifier) into the hard domains of the WPU. Most importantly, platelet adhesion activity, lactate dehydrogenase activity, and erythrocyte or red blood corpuscle lysis demonstrated the hemocompatibility of the developed elastomer. Simultaneously, the cellular viability (live/dead) assay and the cell proliferation (Alamar blue) assay of human dermal fibroblasts corroborated the biocompatibility under in vitro conditions. Furthermore, the synthesized WPUs showed melt re-processability with retention of mechanical strength (86.94%) and microbe-assisted biodegradation. The overall results, therefore, indicate that the developed WPU elastomer might be used as a potential smart biomaterial and coating for biomedical devices.