Intrinsic Self-healing Materials Research Articles

Satisfactory Tensile Strength and Strain of Recyclable Polyurethane with a Trimaleimide Structure for Thermal Self-Healing and Anticorrosive Coatings.

Bismaleimide (BMI) is often used as the cross-linking reagent in Diels-Alder (D-A)-type intrinsic self-healing materials (DISMs) to promote the connectivity of damaged surfaces based on reversible D-A bond formation on the molecular scale. Until now, although DISMs have exhibited great potential in the applications of various sensors, electronic skin, and artificial muscles, it is still difficult to prepare DISMs with satisfactory self-healing abilities and high tensile strengths and strains at the same time, thus largely limiting their applications in self-healing anticorrosive coatings. Herein, symmetrical trimaleimide (TMI) was successfully synthesized, and trimaleimide-structured D-A self-healing polyurethane (TMI-DA-PU) was prepared via the reversible D-A reaction (cycloaddition of furan and maleimide). As a DISM, TMI-DA-PU exhibits apparently higher self-healing efficiency (98.7%), tensile strength (25.4 MPa), and strain (1378%) compared to bismaleimide-structured D-A self-healing polyurethane (BMI-DA-PU) (self-healing efficiency, 90.2%; tensile strength, 19.3 MPa; strain, 1174%). In addition, TMI-DA-PU shows a high recycling efficiency (>95%) after 4 cycles of recycling. A series of characterizations indicate that TMI provides more monoene rings as the self-healing sites, forms denser cross-linked structures compared to BMI, and is, thus, more appropriate to be used for DISM applications. Moreover, the barrier abilities of coatings can be semi-quantitatively expressed by the impedance value at 0.01 Hz (|Z|0.01Hz). The |Z|0.01 Hz value of the TMI-DA-PU coating is 3.93 × 109 Ω cm2 on day 0, which is significantly higher than that of the BMI-DA-PU coating (6.76 × 108 Ω cm2 on day 0), indicating that the denser rigid cross-linked structure of TMI results in the small porosity in the TMI-DA-PU coating, thus effectively improving the anticorrosion performance. The construction of DISMs with the structure of TMI demonstrates immense potential in self-healing anticorrosive coatings.

Preparation of Poly(thiol-urethane) Covalent Adaptable Networks Based on Multiple-Types Dynamic Motifs.

To solve the issue of polymeric materials recycling, developing intrinsic self-healing materials containing dynamic bonds has attracted many researchers' highly concerning. However, the tradeoff between their mechanical strength and stretchability always does not avoid. Herein, to surmount the above tradeoff, metal-ligand (Cu2+ -S) interactions are introduced into the cross-linking polythiourethane covalent adaptable networks (PTU CANs) with three kinds of dynamic motifs (thiourethane, disulfide, and hydrogen bonds). When the molar ratio of Cu2+ to S is 6.37%, the break strength (9.41 ± 0.34MPa)and Young's modulus (26.02 ± 0.55MPa)of the metal-ligand coordination complex PTU (Cu2+ -PTU-3) dramatically increase, whereas the peak strain almost does not decline (454.44 ± 3.95%).To conduct the repairing, Cu2+ -PTU-3 is further confirmed excellent repairing capability. Therefore, these new PTU CANs have significant potential for the new self-healing materials.

Water enabled self-healing polymeric coating with reduced graphene oxide-reinforcement for sensors

Intrinsic self-healing materials have received significant attention due to the characteristic recovery after damage properties through reversible dynamic covalent and non-covalent interactions. Furthermore, functional recovery with reliable mechanical properties are highly keen as protective coatings, specifically for devices and sensors vulnerable to abrasion in severe environments. Here, we present a functional hierarchical nanostructure capable of multiple micro-sized healings, with enhanced mechanical hardness due to the incorporation of graphene oxide (rGO) nanoplatelets. A self-healing multilayered nanocomposite formed by poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA) was easily assembled by the layer-by-layer (LbL) technique. The addition of the rGO nanoplatelets in the LbL nanostructure resulted in a 13-fold increase in hardness (0.4 ± 0.1 GPa) when compared to the (PEI/PAA) architecture (0.03 ± 0.01 GPa). In addition, the nanocomposite presents an enhanced insulating electrical behavior (∼ 4.10−8 S/cm) despite the addition of the rGO nanoplatelets. Raman and Zeta Potential analysis indicated a possible wrapping of the rGOs by PEI, justifying the observed insulating electrical characteristics. The nanocomposite presents good hydrophobicity with a water contact angle of 136°, interesting to extend the lifetime and protect underlying layers from humidity, degradation, and encrustation. Therefore, we propose an attractive hydrophobic, electrically insulating, and mechanically resistant multifunctional coating for high-performance electronic interfaces from minor cuts and abrasions, dispensing maintainer intervention.

Synthesis and application of self-healing elastomers with high healing efficiency and mechical properties based on multi-healing systems

A novel self-healing polyurethane elastomer based on multi-healing systems is presented. In addition, the flexible sensor made of above elastomers doped with conductive graphene can respond to external force quickly and stably. Intrinsic self-healing materials designed by combining reversible valence bonds or ionic coordination have attracted much attention due to their ability to recover from mechanical damage. However, their mechanical properties tend to deteriorate due to the increased rigidity of the chain. In this work, we report a self-healing polyurethane elastomer with multiple healing systems. 3,3′-dithiodipropionic acid (TDPA) and iron ion-2,6-diaminopyridine (DAP) were used as dynamic chain extenders and ionic ligands, respectively. They can be effectively unsealed at a certain temperature to ensure that the self-healing efficiency is not affected by the material formula. By changing the content of hard and soft segments, the mechanical properties and self-healing properties of the material can be adjusted in a large range. When the molar ratio of TDPA and DAP is 0.5:0.5, the polyurethane based on multiple healing system only needs to be healed at 70 °C for 12 h, and the self-healing efficiency can reach 93.48%. The structural rigidity and high reversibility of metal complexing agent DAP and iron ions play an important role in enhancing mechanical strength and maintaining self-healing efficiency at 70 °C. Based on the above research, we prepared the strain sensor by combining self-healing polyurethane and conductive graphene. The sensor can respond to external force quickly and stably. This work provides a feasible strategy for the preparation of mechanically robust polyurethane elastomers and self-healing flexible stress sensors with high self-healing efficiency at 70 °C.

Robust, transparent, and self-healable polyurethane elastomer via dynamic crosslinking of phenol-carbamate bonds

Intrinsic self-healing materials designed through the incorporation of noncovalent interactions or dynamic covalent bonds are prized for their ability to recover from mechanical damages. However, they often suffer from deteriorated mechanical property due to the increased chain mobility. In this work, we reported a high-strength, colorless transparent self-healing polyurethane elastomer through dynamic crosslinking of reversible phenol-carbamate bonds. Tetrabromobisphenol A (TBBPA) and propyl gallate (PG) were used as the dynamic chain extender and dynamic crosslinking agent, respectively. They both can be effectively deblocked at mild temperatures ensuring that the self-healing efficiency is not affected by the material formulation. The mechanical properties can be tailored in a wide range by varying the crosslink density and hard segment content, and their combination uniquely determines the material formulation. The phenol-carbamate based polyurethane (PPU) with a hard segment of 60% and a crosslink density ν of 0.5 mmol cm−3 exhibited a tensile strength up to 46.4 MPa at the break strain of 615% and displayed high elastic resilience. In the meantime, it could be fully healed (ησ = 93%) with 2 h of heating at 100 °C after completely cut off. After recycled three times, it still maintained 80% of its original tensile strength. The structural rigidity of the crosslinker PG and the highly reversible phenol-carbamate bond play a crucial role in strengthening the mechanical strength while maintaining the self-healing efficiencies at elevated temperatures. This work provides a feasible strategy to prepare mechanically robust crosslinked polyurethane elastomer with high self-healing efficiency in a cost-effective manner.

A Brief Overview on Preparation of Self-Healing Polymers and Coatings via Hydrogen Bonding Interactions

Self-healing coatings or materials have received significant importance in paint, coating, and other industries, as well as in academia, because of their capability to extend materials service life, improving protection, and ensuring sustainability. This review article emphasizes significant advances accomplished in the preparation and properties of intrinsic self-healing materials exclusively based on hydrogen bonding interactions, with possible applications in coatings and adhesives. The main topic of discussion in this review article is the preparation, healing conditions, healing efficiency, and mechanical property recovery after healing. The last part of the review discusses the conclusions and outlook of self-healing materials.

Mechanics of bacteria-assisted extrinsic healing

Self-healing materials can typically be divided into two types: intrinsic healing that harnesses dynamic bones to autonomously repair fractures, and extrinsic healing that uses the externally added components to enable the bonding of fractured interfaces. Although the theoretical modeling of intrinsic self-healing materials has been recently studied by Wang et al., the fundamental understanding and theoretical modeling of the extrinsic self-healing materials remain elusive. Without a deep understanding of the extrinsic healing mechanics, the design of extrinsic-healing materials and corresponding applications are still at the trial-and-error stage. Here, taking bacterial-precipitation-enabled healing as an example, we construct a modeling framework to explain the bacteria-assisted extrinsic healing mechanics. A model for the growth of crystal pillars is developed to explain the bacteria-assisted growth of the calcium carbonate (CaCO3) crystal forest within the fracture interface, and a cohesive zone model is built to explain the interfacial bonding. Our modeling framework can explain the evolution of the interfacial healing strength over the healing time and reveal the effects of interface distance and concentrations of bacteria and calcium ions on the healing performance. The modeling results are consistent with the bacteria-assisted healing experiments of ceramics and cement.

TO/TMMP-TMTGE Double-Healing Composite Containing a Transesterification Reversible Matrix and Tung Oil-Loaded Microcapsules for Active Self-Healing.

Thermoset epoxies are widely used due to their excellent properties, but conventional epoxies require a complicated and time-consuming curing process, and they cannot self-healed, which limits their applications in self-healing materials. Extrinsic and intrinsic self-healing materials are applied in various fields due to their respective characteristics, but there is a lack of comparison between the two types of healing systems. Based on this, a thiol-epoxide click reaction catalyzed by an organic base was introduced to achieve the efficient preparation of thiol-epoxy. Furthermore, tung oil (TO)-loaded microcapsules were introduced into the thiol-epoxy matrix of dynamic transesterification to obtain a TO/TMMP-TMTGE self-healing composite with an intrinsic–extrinsic double-healing system. For comparison, a TMMP-TMTGE self-healing material with an intrinsic healing system was also prepared, which contained only thiol and epoxy curing chemistries. The effect of the core/shell ratio on the morphology, average particle size, and core content of TO-loaded microcapsules was studied. It was found that when the core/shell ratio was 3:1, the average particle size of the microcapsules was about 99.8 μm, and the microcapsules showed good monodispersity, as well as a core content of about 58.91%. The differential scanning calorimetry (DSC) results showed that the TO core was successfully encapsulated and remained effective after encapsulation. Furthermore, scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile tests, and electrochemical tests were carried out for the two types of self-healing materials. The results showed that the TO/TMMP-TMTGE composite and TMMP-TMTGE material both had self-healing properties. In addition, the TO/TMMP-TMTGE composite was superior to the TMMP-TMTGE material due to its better self-healing performance, mechanical strength, and corrosion protection performance.

Double network self-healing chitosan/dialdehyde starch-polyvinyl alcohol film for gas separation

Intrinsic self-healing materials have attracted great attention as its self-healing ability endowed by dynamic linkage. In this work, we report a double-network self-healing film which is built by Schiff base linkage between chitosan (CS) and dialdehyde starch (DS), and hydrogen bond between oxygen-containing groups in the polymer. The double-network film has been characterized by the FTIR spectra, thermal decomposition, swelling property, and morphology. The self-healing ability of (CS/DS-PVAx)n film with different concentration of PVA has been measured. The results show self-healing efficiency of (CS/DS)15 film, (CS/DS-PVA5)15 film, (CS/DS-PVA7.5)15 film and (CS/DS-PVA10)15 film is ca. 87.5%, ca.74.2%, ca. 88.4%, and ca. 75.5%, respectively. Meanwhile, the gas separation property is desirable for self-healing (CS/DS-PVAx)n films due to dense structure and amino groups in the film. According to results, (CS/DS-PVA10)15 film performed a CO2/N2 selectivity of 19.8, with ∼18 fold increment in gas selectivity as compared to (CS/DS)15 film. The combination of gas separation property and self-healing property provides a new way to improve the lifetime of gas separation films.

Double Reversible Networks: Improvement of Self-Healing in Hybrid Materials via Combination of Diels–Alder Cross-Linking and Hydrogen Bonds

Intrinsic self-healing materials rely on a reversible bond formation after failure. In this study we report hybrid materials that contain two intrinsic self-healing forces: The reversible covalent ...

Autonomous self-healing supramolecular elastomer reinforced and toughened by graphitic carbon nitride nanosheets tailored for smart anticorrosion coating applications

Intrinsic self-healing materials possessing the capability to autonomously repair their structure and functionalities upon mechanical damage have attracted great attention.

A cohesive-zone crack healing model for self-healing materials

A cohesive zone-based constitutive model, originally developed to model fracture, is extended to include a healing variable to simulate crack healing processes and thus recovery of mechanical properties. The proposed cohesive relation is a composite-type material model that accounts for the properties of both the original and the healing material, which are typically different. The constitutive model is designed to capture multiple healing events, which is relevant for self-healing materials that are capable of generating repeated healing. The model can be implemented in a finite element framework through the use of cohesive elements or the extended finite element method (XFEM). The resulting numerical framework is capable of modeling both extrinsic and intrinsic self-healing materials. Salient features of the model are demonstrated through various homogeneous deformations and healing processes followed by applications of the model to a self-healing material system based on embedded healing particles under non-homogeneous deformations. It is shown that the model is suitable for analyzing and optimizing existing self-healing materials or for designing new self-healing materials with improved lifetime characteristics based on multiple healing events.