High Healing Efficiency Research Articles

Self-Cleaning, Chemically Stable, Reshapeable, Highly Conductive Nanocomposites for Electrical Circuits and Flexible Electronic Devices.

Materials with multiple functions are highly desirable in practical applications. Developing multifunctional nanocomposites by a straightforward process is still a challenge. Here, a versatile nanocomposite has been developed by simple blending and pressing of multiwalled carbon nanotubes (MWCNTs) and modified polydimethylsiloxane (MPDMS). Because of the synergistic effect of MWCNTs and MPDMS, this nanocomposite exhibits outstanding hydrophobic property, striking self-cleaning capability, and excellent chemical stability against strong acid and strong base, which makes it possible to work under wet and even extreme chemical conditions. Besides, because of its flexibility, this nanocomposite can be reshaped, bended, twisted, and molded into on-demand patterns for special applications. Owing to the good distribution of MWCNTs, the nanocomposite shows high conductivity (with a sheet resistance of 86.33 Ω sq-1) and high healing efficiency (above 96.53%) in an electrical field, and it also exhibits outstanding performance in various electrical circuits and flexible electroluminescent devices. Furthermore, the inherent portability, recyclability, and reusability of this nanocomposite make it more convenient and environmentally friendly for practical applications. Thus, our work provides a new strategy to develop a multifunctional nanocomposite, and it shows tremendous potential in flexible electronics.

Enhanced dual-responsive shape memory nanocomposites with rapid and efficient self-healing capability

High-strength nanocomposites were prepared by in situ polymerization of 2-methoxyethyl acrylate and N,N′-dimethylacrylamide with the existence of TiO2 nanoparticles. Based on the reversible hydrogen bond network, the resultant materials showed enhanced mechanical strength, excellent shape memory effect, and superior self-healing capability. To accomplish the goal of rapid and efficient self-healing for the materials, the elevated temperature was chosen as the healing temperature, and the fracture sample could be completely repaired within 10 min with the fracture strength of 13.56 MPa and high healing efficiency of ~ 100% (MD50-T5). Combining the high strain and water-absorbing nature of materials, the recovery of the complex shape of helix structure and self-lacing process in water under physiological temperature could be programmed and finished. Thus, the dual functional elastomers could be used in coating, suturing, and possess the wide application prospects in bioengineering and smart devices.

Heat‐triggered poly(siloxane‐urethane)s based on disulfide bonds for self‐healing application

ABSTRACTPolydimethylsiloxane (PDMS) is one of the most widely employed silicon‐based polymers for its high flexibility, low usage temperature, excellent water resistance, outstanding electrical insulting property, and physiological inert, etc. However, the covalent‐bonded SiO bonds are unable to heal automatically when damaged, which would result in the failure of the materials and devices. Disulfide bond based polymers show high healing efficiency at moderate temperature and have been investigated intensively. Herein, we report a PDMS‐based polyurethane self‐healing polymer (PDMS‐PU) modified with disulfide bonds, which exhibited a reinforced thermal stability, excellent stretchability, and satisfactory self‐healing ability. The effect of different ratio of PDMS and disulfide bond contents on the elastomer properties was investigated. With the increase of PDMS content, the decomposition temperature of the PDMS‐PU‐3 (332 °C) elastomer with highest content of PDMS was increased by 34 °C compared to PDMS‐PU‐1 (298 °C) with lowest content of PDMS and exhibited a largest elongation at break of 1204%. PDMS‐PU‐1 with highest content of disulfide bond possessed a highest healing efficiency of 97%. The results indicated the PDMS‐PU elastomers can be used as self‐healing flexible substrate for flexible electronics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46532.

Design of a self-healing and flame-retardant cyclotriphosphazene-based epoxy vitrimer

Reprocessability and reparability are possible with thermoplastics but are rarely encountered with thermosets, which are used much more frequently in many applications other than thermoplastics. A novel cyclolinear cyclotriphosphazene-based epoxy resin (CTP-EP) was successfully synthesized, characterized, and cured by the addition of the disulfide-containing aromatic diamine hardener DTDA to form a new epoxy vitrimer, CTP-EP/DTDA. This epoxy vitrimer behaves as a typical thermoset at ambient conditions but can be quickly reprocessed at elevated temperatures by hot-pressing, similar to a thermoplastic. The outstanding multi-self-healing performance of this dynamic epoxy system is attributed to the radical-mediated aromatic disulfide exchange mechanism. After repairing itself three times, this epoxy system still had a high healing efficiency of 89.8%. In addition, this newly obtained epoxy system also possesses good thermal stability and excellent flame retardancy due to the cyclotriphosphazene structures in the epoxy resin. The multifunctional properties of this material make it a promising candidate for a variety of applications, such as fiber-reinforced polymer composites in the aerospace and automotive industries.

A thermo-reversible silicone elastomer with remotely controlled self-healing.

Soft thermoplastic elastomers with increased durability and reliability are in high demand for a broad spectrum of applications. Silicone elastomers are soft and durable, but they are not thermoplastic in nature, and under extreme conditions such as high voltage or large deformations, reliability may also suffer. Thus, as a solution to these shortcomings, which are typical of silicone elastomers, it is natural to propose a thermo-reversible, self-healing, and recyclable silicone-based elastomer. Stimuli-responsivity is imparted to the silicone polymer by incorporating supramolecular 2-ureido-4[1H]-pyrimidone (UPy) self-assembling motifs via free radical polymerisation. Self-healing of the novel elastomer may be triggered by both direct and indirect heating, the latter by means of incorporating Fe3O4 particles into the elastomer and subsequent exposure to an alternating magnetic field. As a consequence of temperature responsiveness and high thermal stability, the elastomer is proven recyclable, by withstanding multiple reprocessing procedures with no substantial effects on the resulting properties. The synergy of these valuable characteristics makes this novel material a smart candidate for innumerable applications where soft and reliable elastomers are sought.

The effect of electron density in furan pendant group on thermal-reversible Diels-Alder reaction based self-healing properties of polymethacrylate derivatives.

Herein, we discuss the effect of electron density in a furan pendant group on the thermally reversible Diels–Alder (DA) reaction based self-healing efficiency in polymethacrylate derivatives. First, the furan-functionalized polymethacrylates (rPFMA and dPFMA) having different electron density in the furan pendant groups were prepared through free-radical polymerization. The healing efficiency of rPFMA, which was expected to have high healing efficiency due to the high reactivity of DA reaction originating from the electron density in the furan moiety, was shown to be 95.89% in the first and 69.86% in the second healing process, respectively, where it is higher than that of dPFMA having relatively low electron density in the furan moiety. To illustrate these results, kinetic tests of the DA reaction for rPFMA64 and dPFMA64 were performed, where the reactivity of the DA reaction for rPFMA64 was much higher than that for dPFMA64. This could be explained by the electron density in the furan pendant groups which controls the reactivity of DA reaction having a major effect on the efficiency of self-healing performance in furan-functionalized polymethacrylates.

Self-Healing Sensors Based on Dual Noncovalent Network Elastomer for Human Motion Monitoring.

Nowadays, it is still a challenge to prepare flexible sensors with great mechanical strength, stretchability, high sensitivities, and excellent self-healing (SH) abilities. Herein, a nanostructured supramolecular elastomer is reported with a dual noncovalent network of hydrogen bonding interactions and metal-ligand coordination. The resultant flexible sensor presents ultrafast (30 s), autonomous, and repeatable SH ability with high healing efficiency (80% after the 3rd healing process), as well as enhanced mechanical properties. Benefitting from the 3D conductive network, the sensor exhibits high electrical sensitivity and very low detection limit (0.2% strain). As a result, the flexible sensor is capable of precisely monitoring small strains of human motions (such as vocal-cord vibration), and exhibits reproducible and recognizable current signals after cutting-healing process. The dual noncovalent network design proposed here opens up a new opportunity for scalable fabrication of high performance SH sensors and other electronic devices.

Highly Efficient Self‐Healable and Dual Responsive Cellulose‐Based Hydrogels for Controlled Release and 3D Cell Culture

AbstractTo face the increasing demand of self‐healing hydrogels with biocompatibility and high performances, a new class of cellulose‐based self‐healing hydrogels are constructed through dynamic covalent acylhydrazone linkages. The carboxyethyl cellulose‐graft‐dithiodipropionate dihydrazide and dibenzaldehyde‐terminated poly(ethylene glycol) are synthesized, and then the hydrogels are formed from their mixed solutions under 4‐amino‐DL‐phenylalanine (4a‐Phe) catalysis. The chemical structure, as well as microscopic morphologies, gelation times, mechanical and self‐healing performances of the hydrogels are investigated with 1H NMR, Fourier transform infrared spectroscopy, atomic force microscopy, rheological and compression measurements. Their gelation times can be controlled by varying the total polymer concentration or 4a‐Phe content. The resulted hydrogels exhibit excellent self‐healing ability with a high healing efficiency (≈96%) and good mechanical properties. Moreover, the hydrogels display pH/redox dual responsive sol‐gel transition behaviors, and are applied successfully to the controlled release of doxorubicin. Importantly, benefitting from the excellent biocompatibility and the reversibly cross‐linked networks, the hydrogels can function as suitable 3D culture scaffolds for L929 cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the cellulose‐based self‐healing hydrogels show potential applications in drug delivery and 3D cell culture for tissue engineering.

Understanding the role of internal microstructure in capsule‐based healing of polymeric composites

ABSTRACTThe efficacy of microcapsules possessing varied internal microstructure toward introducing extrinsic self‐healing functionality in epoxy has been compared. Unsaturated polyester was encapsulated in microcapsules by adopting different methodologies. Microcapsules formed using dispersion polymerization exhibited “reservoir” microstructure while solvent evaporation led to the formation of “monolithic” microcapsules. Theoretical model was developed to predict the amount of healant released in the event of microcapsule rupture, which clearly highlighted the benefits associated with reservoir type microcapsules, especially at lower core contents. At larger core contents (≥50% vol/vol), all the micro‐droplets within the monolithic structure coalesced to form a healant reservoir. Self‐healing composites were prepared by introducing both types of microcapsules in an epoxy matrix and the healing efficiency was quantified. In line with the theoretical predictions, reservoir type microcapsules led to much higher healing efficiencies in comparison to monolithic microcapsules. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45471.

Multiple Hydrogen Bonding Enables the Self‐Healing of Sensors for Human–Machine Interactions

AbstractDespite its widespread use in signal collection, flexible sensors have been rarely used in human–machine interactions owing to its indistinguishable signal, poor reliability, and poor stability when inflicted with unavoidable scratches and/or mechanical cuts. A highly sensitive and self‐healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network is demonstrated. The nanostructured supramolecular sensor displays extremely fast (ca. 15 s) and repeatable self‐healing ability with high healing efficiency (93 % after the third healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting–healing and bending over 20 000 cycles. Furthermore, a human–machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the mute to realize real‐time speaking.

Multiple Hydrogen Bonding Enables the Self-Healing of Sensors for Human-Machine Interactions.

Despite its widespread use in signal collection, flexible sensors have been rarely used in human-machine interactions owing to its indistinguishable signal, poor reliability, and poor stability when inflicted with unavoidable scratches and/or mechanical cuts. A highly sensitive and self-healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network is demonstrated. The nanostructured supramolecular sensor displays extremely fast (ca. 15 s) and repeatable self-healing ability with high healing efficiency (93 % after the third healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting-healing and bending over 20 000 cycles. Furthermore, a human-machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the mute to realize real-time speaking.

Electrospun Poly(styrene) Fibers as a Protection for the First- and the Second-Generation Grubbs’ Catalyst

ABSTRACTThe study presents a novel method for protection of the first- and the second-generation Grubbs’ catalyst, by incorporation in poly(styrene) fibers through electrospinning technique. Both catalysts are sensitive to the presence of the amine hardeners in the epoxy-based self-healing composites and require protection from deactivation to retain their ability to promote polymerization reaction of the healing agent. Comparison of healing efficiencies of both catalysts suggested that poly(styrene) fibers offer better protection and dispersion for the first-generation Grubbs’ catalyst, although all the samples exhibited high-healing efficiency. Difference in stereoselectivity between two catalysts was also indicated.

A stretchable polysiloxane elastomer with self-healing capacity at room temperature and solvatochromic properties.

A stretchable silicon elastomer comprising cobalt ions in pyridine pendant polydimethylsiloxane (PDMS) was prepared. Different from previously reported cobalt-coordinated elastomers, these elastomers are self-healable at room temperature with a high healing efficiency of over 90%. Besides, they exhibit tailored solvatochromic properties over a wide range without sacrificing its self-healing ability at room-temperature.

Homogeneous and Heterogeneous Solid State Self-Healing System

The solid state self-healing system was obtained by employing a thermosetting epoxy resin, into which a thermoplastic is dissolved. The aim of this study is to investigate the homogeneous and heterogeneous solid state self-healing system by using thermoplastics comprised of poly(bisphenol-A-co-epichlorohydrin) (PDGEBA), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyethylene (PE) and polypropylene (PP) as healing agents. PDGEBA produced homogenous resin blend which undergone random molecule diffusion healing process. A heterogeneous resin blend composed of 8 wt.% PVC, PVA PE, and PP, yielding a “bricks and mortar” morphology wherein the epoxy phase exists as a matrix (mortar) interpenetrated with a percolating thermoplastic (bricks). The healing process in heterogeneous resin blend is attributed to volumetric thermal expansion of healing agent above its melting point in excess of epoxy brick expansion. Healing was achieved by heating the fractured resins to a specific temperature; above their glass transition temperature ( Tg) which obtained from dynamic mechanical analysis (DMA) in order for diffusion process and thermal expansion to occur. The thermal properties and bonding formed in the epoxy resins were characterized by means of Fourier Transform Infrared Spectroscopy (FTIR) and dynamic mechanical thermal analysis (DMTA). Izod impact test and compact tension test were conducted to demonstrate details self-healing capability of different specimens. Results of Izod impact test are in agreement with the result of compact tension test. Under compact tension test, the healable resin with PDGEBA has the highest healing efficiency of 60% followed by PVC, PP, PE, and PVA with 39%, 37%, 28% and 21% of average percentage healing efficiencies in three healing cycle respectively. Morphological studies using optical microscope verified the fracture-healing process and morphological properties of the resins.

Intrinsic healable and recyclable thermoset epoxy based on shape memory effect and transesterification reaction

A shape memory and healable epoxy was prepared based on esterification between diglycidyl ether of bisphenol A and tricarballylic acid. The healing was achieved through transesterification at the fracture surface between two epoxy blocks in a confined space assisted by shape recovery force. The shape recovery of the compression programmed epoxy at elevated temperature tightly closed the gap between the two epoxy blocks, whose fracture surfaces are saw-cut and not perfectly matched during healing, which is the worst case scenario for the healing test. A healing efficiency of ∼60% was achieved. This suggests that, for naturally cracked surfaces, which have smoother fracture surfaces and better surface alignments during healing, higher healing efficiencies could be expected. We believe that the combination of shape memory and intrinsic healing capability within one network will broaden the applications of thermosets and enable recycling.

Self-healing glass fiber/epoxy composites with polypropylene tubes containing self-pressurized epoxy and mercaptan healing agents

To improve flowability of the healing agent released from micropipelines without manual intervention, this work prepared a proof-of-concept self-healing glass fiber/epoxy composite, in which plastic (polypropylene (PP)) tubes were embedded and used as containers of epoxy/mercaptan healing agent and foaming agent. Decomposition of the foaming agent at 70 °C created inflated gas in the sealed PP tubes in advance, which increased the internal pressure. Upon damage of the composite, the pressurized healing fluid burst out covering larger cracked plane and enhanced mixing of the liberated epoxy monomer and hardener. As a result, higher healing efficiency was observed as compared to the case without pressurization. The factors that influence healing performance of the system (e.g., tube spacing, content of the foaming agent, foaming time, etc.) were discussed in detail. The proposed approach is believed to have adequate expansibility and can be applied in other self-healing composites with micropipelines.

Fishing line artificial muscle reinforced composite for impact mitigation and on-demand damage healing

In this study, a fishing line artificial muscle reinforced syntactic foam composite was investigated. About 3.5 vol.% of polymer artificial muscle was woven into a two-dimensional grid skeleton and embedded into a syntactic foam matrix. The grid-stiffened syntactic foam composite was designed to be able to repeatedly heal cracks on-demand. Short thermoplastic fibers were also dispersed into the foam matrix both as reinforcement and as a healing agent. The composite panel was repeatedly impacted, bending fractured, and healed as per the biomimetic close-then-heal strategy. It is found that the composite panel responds to impact quasi-statically. The impact- and bending-induced macroscopic cracks can be repeatedly healed with high healing efficiency, under both free and clamped boundary conditions. Contrary to most healing systems, the healing efficiency within the damage–healing cycles in this study increases as the damage-healing cycle increases. Because the artificial muscle is made of low-cost and high-strength fishing line, it is envisioned that the composite panel developed in this study may be a viable alternative core for healable lightweight composite sandwich structures at competitive cost.

Novel Diels-Alder based self-healing epoxies for aerospace composites

Epoxy resins containing Diels-Alder (DA) furan and maleimide moieties are presented with the capability to self-heal after exposure to an external heat source. A conventional epoxy amine system has been combined with furfuryl and maleimide functional groups in a two-step process, to avoid major side-reactions, and the concentration of a thermo-reversibly binding cross-linker was considered to balance thermoset and thermoplastic behaviours, and the subsequent self-healing performance. In the context of self-repair technologies an inbuilt ‘intrinsic’ self-healing system is deemed favourable as the healing agent can be placed in known ‘hot spot’ regions (i.e. skin-stringer run outs, ply drops and around drilled holes) where operational damage predominately occurs in load bearing aerospace structures. In this study, the mechanical and self-healing performance of furan functionalised epoxy resins containing varying amounts (10, 20, 30 or 40 pph) of bismaleimide were investigated using a bulk epoxy polymer tapered double cantilever beam test specimen geometry. Two forms, a thin film and a bulk material, were evaluated to account for future integration methods into fibre reinforced polymer (FRP) composites. The highest healing efficiency, with respect to the obtained initial load value, was observed from the 20 pph bulk material derivative. The polymers were successful in achieving consistent multiple (three) healing cycles when heated at 150 °C for 5 min. This novel investigated DA material exhibits favourable processing characteristics for FRP composites as preliminary studies have shown successful coextrution with reinforcing fibres to form free standing films and dry fibre impregnation.

自己修復性を有する開繊炭素繊維／エポキシ樹脂積層材料の強度回復と微視構造最適化

Damage can cause a reduction in the strength and stiffness in FRP and is very difficult to detect and repair. Thus, self-healing has the potential to mitigate damage in FRP. This study examines the effect of microcapsule concentration and diameter on the strength recovery of spread carbon fiber(SCF)/epoxy(EP) laminates encompassing self-healing. Healing is accomplished by incorporating a microencapsulated healing agent and catalyst. Self-healing is demonstrated on short beam shear specimens and the healing efficiency was evaluated by the strain energies of virgin and healed specimens. The damaged area of specimens was also examined by an optical microscope. The results showed that as the microcapsule concentration increased, the apparent interlaminar shear strength decreased and the healing efficiency increased. The trade-off between the strength and the healing efficiency was observed. Furthermore, as the microcapsule diameter increased, the apparent interlaminar shear strength decreased. High healing efficiency was achieved with 50μm microcapsule diameter.

Self-healing poly(siloxane-urethane) elastomers with remoldability, shape memory and biocompatibility

The poly(siloxane-urethane) elastomers with microphase separation structure and Diels–Alder bonds show high healing efficiency, good mechanical property and good biocompatibility.