High Self-healing Efficiency Research Articles

Surface modified halloysite nanotube enhanced imine-based epoxy composites with high self-healing efficiency and excellent mechanical properties

(a) Schematic diagram of the self-healing mechanism. (b) Illustration of the cross-linking effect and the internal molecular structure.

Electron-Donating Effect Enabled Simultaneous Improvement on the Mechanical and Self-Healing Properties of Bromobutyl Rubber Ionomers.

Due to the dynamic nature of networks and high mobility of molecular chains, self-healing elastomers are usually confronted with the trade-off between self-healing efficiency and mechanical properties. Herein, a self-healing ionomer with both high mechanical performance and high self-healing efficiency has been successfully developed by grafting bromobutyl rubber (BIIR) with pyridine-based derivatives. Interestingly, the substituents on the pyridine ring can be used to regulate the interaction forces of ionic clusters and molecular dynamics. The electron-donating effect of the substituents facilitates stable π-π stacking between pyridyl ions, inducing the formation of regular and large ion aggregates, thereby improving the mechanical strength of the ionomer. Meanwhile, the plasticizing effect of the substituents reduces the activation energy and relaxation temperature of the ionic aggregates, thus endowing the ionomer with a high self-healing efficiency. As a result, the ionomer shows tensile strength as high as 8.1 ± 0.3 MPa under room temperature and self-healing efficiency of 100 ± 3% at 60 °C. Therefore, this strategy can be easily extended to other halogen-containing polymers, leading to a novel class of self-healing ionomers that hold great promise in diverse applications.

Facile immobilization of graphene nanosheets onto PBO fibers via MOF-mediated coagulation strategy: Multifunctional interface with self-healing and ultraviolet-resistance performance

The surface of poly (p-phenylene benzobisoxazole) (PBO) fibers with self-healing and ultraviolet (UV)-resistance performance play the key role in prolonging their service lifespan. Although great advances have been made in the single aspect of above two properties, integration of self-healing and anti-UV performance into the surface of PBO fiber is still a challenge. In this study, the coagulation strategy mediated by metal-organic framework (MOF) is proposed to construct the multifunctional surface of PBO fibers. The spindle-like iron (III)-based MOF (MIL-88B-NH2) nanocrystals are firstly immobilized onto the surface of PBO-COOH through hydrothermal reaction, then serving as the medium layer to further immobilize sufficient graphene oxide (GO) nanosheets. Benefitting from the favorable near-infrared (NIR, 808 nm) photothermal conversion performance of GO nanolayers, the monofilament composite-PBO@Fe-MIL-88B-NH2-GO-TPU (thermoplastic polyurethane) exhibited a stable and high self-healing efficiency (approximately 80%) within five cycle times. Meanwhile, the cooperative adsorption and shielding weaken effects of MOF-GO nanolayers enabled PBO fibers with excellent anti-UV properties that are superior to much reported literatures after 96 h aging time and eventually increased by 75% compared with untreated PBO fiber. In view of the varieties and multifunctionalities of MOFs and carbon nanomaterials, MOF-mediated coagulation strategy would provide guidance for preparing multifunctional composite materials.

Mussel-inspired double cross-linked hydrogels with desirable mechanical properties, strong tissue-adhesiveness, self-healing properties and antibacterial properties

Developing multifunctional hydrogels with good mechanical properties, tissue-adhesiveness, self-healing properties and antioxidant, blood clotting and antibacterial properties is highly desirable for biomedical applications. In this study, a series of multifunctional chitosan-based double cross-linked hydrogels were prepared using a facile method based on quaternized chitosan (QCS) and polyacrylamide (PAM) using polydopamine (PDA) as a novel connecting bridge. Investigation on the content of dopamine (DA) and QCS revealed that the catechol-mediated interactions played an important role in the hydrogel properties. Results showed that the hydrogel exhibited the best mechanical properties when QCS = 12 wt% and DA = 0.4 wt%. Tensile and compressive strength was 13.3 kPa and 67.8 kPa, respectively, and the hydrogel presented strong and repeatable tissue-adhesiveness (27.2 kPa) to porcine skin, as well as good stretchability (1154%). At room temperature, the hydrogel exhibited high self-healing efficiency (90% after 2 h of healing). Antibacterial test results showed that the hydrogel killed 99.99% S. aureus and E. coli. Moreover, the vaccarin-loaded hydrogel exhibited a pH-responsive drug release profile with superior cytocompatibility compared to the pure hydrogel. In summary, this strategy combined double cross-linking and catechol-mediated chemistry to shed new light on the fabrication of novel multifunctional hydrogels with desirable mechanical properties, strong tissue adhesiveness and self-healing abilities.

Getting self-healing ability and ultra-low dielectric loss for high-k epoxy resin composites through building networks based on Li0.3Ti0.02Ni0.68O grafted carbon nanotube bundles with unique surface architecture

Getting self-healing ability and ultra-low dielectric loss is effective to achieve high service reliability and sustainable development for high dielectric constant (high-k) polymer composites. Herein, new functional fillers with special surface architecture (sLTNO@mAC) were synthesized by grafting Li0.3Ti0.02Ni0.68O particles (sLTNO) on surfaces of carbon nanotube bundles (mAC), which was then embedded in epoxy resin (EP) with disulfide bonds to develop new composites (sLTNO@mAC/EP). Compared with composites based on mAC (mAC/EP) or a blend of sLTNO and mAC (sLTNO/mAC/EP) with the same filler loading, sLTNO@mAC/EP composites have much higher dielectric constant and self-healing efficiency as well as much lower dielectric loss at the same frequency. For the composite based on sLTNO@mAC with 8.2 wt% of sLTNO, coded as sLTNO1@mAC/EP, its dielectric loss is only 0.02, about 1.1 × 10 -3 and 9.4 × 10 -3 times of that of mAC/EP and sLTNO/mAC/EP, respectively; meanwhile its dielectric constant (216.1, 100 Hz) is the highest value among self-healable dielectric composites reported so far, and sLTNO1@mAC/EP has higher self-healing efficiency (97.7%) than mAC/EP and sLTNO/mAC/EP. The mechanism behind these attractive properties reveals that dielectric properties of sLTNO@mAC/EP mainly depend on interface polarization, while those of mAC/EP and sLTNO/mAC/EP are mainly related to the integrity of conductive networks.

Ethyl cellulose based self-healing adhesives synthesized via RAFT and aromatic schiff-base chemistry

In this work, reversible addition-fragmentation chain transfer (RAFT) polymerization and Schiff base chemistry was combined to fabricate self-healing adhesives. An esterification reaction was first performed to prepare ethyl cellulose based macroinitiators. Then, a “grafting from” RAFT of vanillin methacrylate and lauryl methacrylate was used to obtain graft copolymers. DSC result showed that the glass transition temperature was manipulated via changing the ratio of vanillin and fatty acids moieties. NMR spectrum analysis demonstrated the presence of aldehyde groups, which were available for the dynamic crosslinking to generate a network as self-healing adhesives. The adhesive test showed that the shear strength could reach 0.81 MPa with a self-healing efficiency of 98.7 %. The bottlebrush structures of copolymers and reversibility of Schiff base chemistry might collaboratively contribute to the high self-healing efficiency. This study provides a facile way to fabricate high-performance self-healing adhesives from ethyl cellulose and renewable resources.

Highly stretchable and self-healing strain sensors for motion detection in wireless human-machine interface

Abstract The highly stretchable, flexible and self-healing strain sensor is considered as a promising wearable device for motion detection in fields such as robotics and human-machine interface. Herein, a strain sensor with high stretchability and sensitivity is designed and fabricated based on the poly(acrylamide) (PAAm) hydrogel. The ionic conductive PAAm hydrogel shows an excellent self-healing property with fast electrical self-healing speed (within 1.8 s) and high self-healing efficiency (99%). The PAAm hydrogel based strain sensor exhibits excellent performance with large stretchability (>900%), high sensitivity (with maximum gauge factor of 6.44), fast response time (~150 ms), and good cycling durability (>3000 cycles). As the wearable device, the strain sensor can detect various human motions and is able to transmit the data to the smart phone combined with a readout and wireless system. Furthermore, a smart glove was fabricated by coupling multiple strain sensors and the corresponding circuit. The smart glove is capable of expressing and recognizing American Sign Language and can be used to control a robotic hand wirelessly through the hand gestures. Thus, the highly stretchable, self-healing hydrogel-based strain sensor shows a potential application for the human-machine interface, personal healthcare and sports training.

Construction of a Dual Ionic Network in Natural Rubber with High Self-Healing Efficiency through Anionic Mechanism

Even though considerable efforts have been applied toward self-healing materials, construction of a reversible network in a nonpolar elastomer with a high strength and self-healing behavior is stil...

Ultrasensitive and robust self-healing composite films with reinforcement of multi-branched cellulose nanocrystals

Herein, self-healing multi-branched cellulose nanocrystals/polyvinyl alcohol (MCNC/PVA) composite films with excellent sensitivity to human motions was synthesized by employing MCNC as reinforcing agent, where the potassium chloride (KCl) was added to enhance the conductivity and strain sensitivity of the composite film. There was a synergistic effect between MCNC and PVA, which could promote the slip and recombination of hydrogen bonds, so that the films had robust strength (2.2 times to pure PVA) and high self-healing efficiency (69.54% after 20 min). Especially, the flexible composite film could clearly monitor both large and subtle human motions (finger bending, swallowing, breathing, and insect crawling), and showed larger subtle strain sensitivity (strains <24.5%) with a gauge factor (GF) of 2.4, which was relatively larger than the GF of ionic hydrogel and film-based skin sensors, which could solve the current problems of poor mechanical flexibility and low sensitivity of electronic skin, and had great potential application in the fields of self-healing soft electronic skin sensors for human motion detection and healthcare.

Microscopic Tests on Evaluation of Self-Healing Efficiency in Cementitious Materials with a Novel Self-Healing System

In this study, Na2CO3 solution as a self-healing agent was impregnated in LWA for autonomic self-healing on cracked cementitious material. The results showed that under the joint action of expansive agent, crystalline additive, phosphate and carbonate, the crack area showed a high self-healing efficiency (close to 70%) after curing in the still water 28d. SEM-EDS test results showed that in addition to ettringite and C-S-H/C-A-S-H, there was also a large amount of CaCO3 crystal in the depths of the crack.

Readily self-healing polymers at subzero temperature enabled by dual cooperative crosslink strategy for smart paint

Achieving the artificial supramolecular polymer with excellent low temperature self-healing capability has been a new topic of great significance in soft robotic actuators and smart coating. Nevertheless, the production of robust polymer with decent low temperature self-healing ability is severely impeded by its high crosslink density and low dynamic crosslink bond. Here, we report a design strategy that both low crosslink density and high dynamic crosslink bonds are introduced into polyurea networks to achieve a tough and low-temperature healable supramolecular system of polypropyleneglycol (PPG)-polydimethylsiloxane (PDMS)-Zn (abbreviated as PPG-PDMS-Zn). Incorporating the long PPG segments into linear PDMS chains endows the resulting polymer with relatively low crosslink density, allowing fast polymer chains movement to unite fractured surfaces. Moreover, the dynamic characteristics and self-healing capability of the supramolecular network were effectively enhanced by combining the unique dynamic exchange feature of weak Zn-urethane coordination bonds and low temperature inhibition-dissociation effect of hydrogen bonds. As a result, the representative sample of PPG-PDMS-Zn-0.5 polymer displays a robust tensile strength of 0.98 MPa and a high self-healing efficiency of 97% at −20 °C, and these features have rarely been achieved in the previously reported materials. With these promising characters, such kind of supramolecular polymers can find wide applications in fields of anti-icing and winter anti-frosting paints, and antarctic pole exploration as well.

Influence of Morphology on the Healing Mechanism of PCL/Epoxy Blends.

Polycaprolactone (PCL) is being researched as a self-healing agent blended with epoxy resins by several reasons: low melting point, differential expansive bleeding (DBE) of PCL, and reaction induced phase separation (RIPS) of PCL/epoxy blends. In this work, PCL/epoxy blends were prepared with different PCL ratios and two different epoxy networks, cured with aliphatic and aromatic amine hardeners. The curing kinetic affects to the blend morphology, varying its critical composition. The self-healing behavior is strongly affected by the blend morphology, reaching the maximum efficiency for co-continuous phases. Blends with dispersed PCL phase into epoxy matrix can also show high self-healing efficiency because of the low PCL domains that act as reservoir of self-healing agent. In this last case, it was confirmed that the most efficient self-healable blends are one whose area occupied by PCL phase is the largest. These blends remain the good thermal and mechanical behavior of epoxy matrix, in contrast to the worsened properties of blends with bicontinuous morphology. In this work, the self-healing mechanism of blends is studied in depth by scanning electron microscopy. Furthermore, the influence of the geometry of the initial surface damage is also evaluated, affecting to the measurement of self-healing efficiency.

Synthesis and characterization of self-healing cross-linked non-isocyanate polyurethanes based on Diels-Alder reaction with unsaturated polyester

A green method is established to prepare soft self-healing cross-linked non-isocyanate polyurethanes (SH-NIPUs). Three non-isocyanate polyurethane prepolymers with furan terminal groups (F-NIPUs) were synthesized through a ring-opening reaction of diglycerol bis(cyclic carbonate) with isophoronediamine and furfurylamine under mild reaction conditions. New SH-NIPUs were prepared via a Diels–Alder reaction between F-NIPUs and unsaturated polyester. The obtained SH-NIPUs were characterized by 1H NMR, ATI-FTIR, DSC, polarized optical microscope, and tensile strength after being damaged and healed. The SH-NIPUs exhibited a Tg between -4 and 20 °C, and a relatively low reverse Diels–Alder temperature between 90 and 100 °C. Soft SH-NIPUs with high self-healing efficiency up to 100% were achieved successfully.

Self-Healing Solid Polymer Electrolyte Facilitated by a Dynamic Cross-Linked Polymer Matrix for Lithium-Ion Batteries

Compared with liquid electrolytes, the solid polymer electrolyte (SPE), which possesses improved thermal and mechanical stability, is believed the broadest potential application for satisfying the safety needs of advanced electrochemical devices. However, some breakable SPEs could lead to catastrophic failure of batteries that triggered by a short circuit. In the present contribution, a new class of SPE containing disulfide bonds and urea groups is reported. The hydrogen bonding between the urea groups and disulfide metathesis reaction endows the SPE with a high level of self-healing without external stimuli at room temperature as well as ultrafast self-healing at elevated temperatures. The completely healed SPE with extreme damage shows a high self-healing efficiency and no changes in the ionic conductivity and cycling performance of the solid-state lithium-metal/LiFePO4 cell compared to the pristine one.

Self-Healing and Highly Stretchable Gelatin Hydrogel for Self-Powered Strain Sensor.

Hydrogels that electronically respond to mechanical changes can be used as strain sensors. However, these systems usually require external power to convert changes in strain into electrical signals. Here, a self-powered strain sensor is developed based on a gelatin-based hydrogel and a galvanic cell. In the hydrogel matrix, hydrophobic interactions and hydrogen bonding between tannic acid and gelatin give the prepared hydrogel great potential for elongation (1600%). The hydrogel also has a rapid self-healing ability (within 0.65 s) and high self-healing efficiency (95%). The hydrogel operates as an efficient electrolyte material and forms a hydrogel battery when assembled with a thin layer of zinc and an air electrode. This device had excellent tolerance to large compressional strain without sacrificing open-circuit voltage. On the basis of this hydrogel battery, we fabricated a self-powered strain sensor by connecting the hydrogel battery to a fixed resistor to form a closed loop. By converting its chemical energy into electrical energy, the self-powered sensor efficiently converted resistance changes, caused by stretching or compression of the hydrogel, into changes in the voltage output signals without external power. Owing to the stretchability of the hydrogel, the self-powered sensor exhibited good response and flexibility. Self-healing and continuous cycling tests confirmed the long-term stability of the device. These properties suggest that our self-powered sensor has a potential for applications to portable and wearable electronic devices.

A Skin-Inspired Stretchable, Self-Healing and Electro-Conductive Hydrogel with A Synergistic Triple Network for Wearable Strain Sensors Applied in Human-Motion Detection.

Hydrogel-based strain sensors inspired by nature have attracted tremendous attention for their promising applications in advanced wearable electronics. Nevertheless, achieving a skin-like stretchable conductive hydrogel with synergistic characteristics, such as ideal stretchability, excellent sensing performance and high self-healing efficiency, remains challenging. Herein, a highly stretchable, self-healing and electro-conductive hydrogel with a hierarchically triple-network structure was developed through a facile two-step preparation process. Firstly, 2, 2, 6, 6-tetrametylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils were homogeneously dispersed into polyacrylic acid hydrogel, with the presence of ferric ions as an ionic crosslinker to synthesize TEMPO-oxidized cellulose nanofibrils/polyacrylic acid hydrogel via a one-pot free radical polymerization. A polypyrrole conductive network was then incorporated into the synthetic hydrogel matrix as the third-level gel network by polymerizing pyrrole monomers. The hierarchical 3D network was mutually interlocked through hydrogen bonds, ionic coordination interactions and physical entanglements of polymer chains to achieve the target composite hydrogels with a homogeneous texture, enhanced mechanical stretchability (elongation at break of ~890%), high viscoelasticity (maximum storage modulus of ~27.1 kPa), intrinsic self-healing ability (electrical and mechanical healing efficiencies of ~99.4% and 98.3%) and ideal electro-conductibility (~3.9 S m−1). The strain sensor assembled by the hybrid hydrogel, with a desired gauge factor of ~7.3, exhibits a sensitive, fast and stable current response for monitoring small/large-scale human movements in real-time, demonstrating promising applications in damage-free wearable electronics.

Mechanically robust self-healing and recyclable flame-retarded polyurethane elastomer based on thermoreversible crosslinking network and multiple hydrogen bonds

Self-healing polymers have drawn significant attention because of their great potential for applications in many fields. It is highly desirable to prepare materials capable of self-healing and with excellent mechanical properties. Additionally, the flammability of polymers make them unsafe during use. A novel strategy is proposed to manufacture a multifunctional polyurethane elastomer with high tensile strength (37.11 ± 1.89 MPa) and excellent self-healing efficiency (91.8%), containing a thermo-reversible crosslinking network and multiple hydrogen interactions. The furan-terminated phosphorus-based monomer, tri(2-furyl) phosphoramide (TFP), was successfully synthesized and then conjugated into a maleimide-terminated linear segmented polyurethane (MPU) backbone to prepare self-healing, recyclable, and flame-retarded polyurethane (MPUF). Due to its synergetic dual reversible bonds, the multifunctional polyurethane elastomer possessed ultrahigh strength, and excellent self-healing, shape recovery, and reprocessing properties. The phosphorus containing polyurethane elastomer exhibited improved thermal stability a limiting oxygen index value of 28.5%, and a 12.3% decrease in the peak heat release rate (pHRR) relative to those of unmodified polyurethane. This work demonstrates an effective strategy to prepare multifunctional polyurethane elastomer with both high self-healing efficiency and excellent mechanical properties allowing application for this material in the fields of fire-control coatings and building materials.

A self-healing silicone/BN composite with efficient healing property and improved thermal conductivities

Polymer dielectric composites with excellent thermal conductivity have received increasing attention in the modern electronics industry due to their outstanding thermal management performance. However, conventional polymers used for the thermally conductive composites usually suffer from accidental mechanical failure, causing decrease in service life or loss of functionality. In this work, we prepared a self-healing silicone/BN composite simultaneous with high thermal conductivity, high self-healing efficiency and low electrical conductivity. Silicone cross-linked by DA adduct was used as polymer matrix and BN was used as thermally conductive filler. The self-healing silicone/BN composite exhibited a high self-healing efficiency of higher than 90% and an enhancement of 544% in thermal conductivity at BN content of 50 wt%. The self-healing composites presented excellent thermal management performance. The excellent self-healing properties were attributed to the thermal reversibility of the DA reaction and the flexibility of the siloxane molecules. In addition, the self-healing silicone/BN composite with 50 wt% of BN exhibited a low dielectric dissipation factor of 0.017 and an enhancement of 568% in tensile strength.

Silicone dielectric elastomer with improved actuated strain at low electric field and high self-healing efficiency by constructing supramolecular network

Dielectric elastomers (DE) suffer from cracks and breaks during repeated cycles, thus a DE material with both high actuated strain (SA) and self-healing ability is highly desired. Herein, for the first time we report a self-healable silicone DE (SiR-SN) with large SA under low electric field by constructing supramolecular network assembled by hydrogen bonds and ionic bonds from two components involving carboxyl modified polymethylvinylsiloxane (PMS-g-COOH) and amino terminated polydimethylsiloxane (PDMS-NH2). The results show that as PMS-g-COOH content increases, the dielectric constant (ε′) of SiR-SN increases owing to an increase in dipole content whereas the elastic modulus (Y) decreases because of a decrease in crosslinking density, leading to the significantly increased SA at a given electric field. SiR-SN with 0.2/1 of the mass ratio of PMS-g-COOH to PDMS-NH2 shows much higher ε′ and SA than the commercial silicone DE. Interestingly, self-healing of SiR-SN at 80 °C leads to the re-formation of hydrogen bonds, and thus the recovery of network structure, whereas self-healing at 100 °C can lead to the conversion from hydrogen bonds into ionic ones, and thus the change of network structure. As a result, a self-healing efficiency of 115% in tensile strength and almost 100% in SA at a given electric field can be achieved after self-healing at 80 °C for 5 h, whereas an increase in Y and higher breakdown strength can be achieved after self-healing at 100 °C, which may sustain the repeated stress and prolong the service life. It is promising that this new self-healable silicone dielectric elastomer with large actuated strain under low electric field could be used especially in biological and medical fields.

Room temperature readily self-healing polymer via rationally designing molecular chain and crosslinking bond for flexible electrical sensor

Mechanically tough polymers with excellent room temperature self-healing capacity have aroused strong interest in soft electronics, electronic skins and flexible energy storage devices. However, achieving such polymers remains a challenge due to tardy diffusion dynamics. Herein, a robust and readily self-healing polymer, which is synthesized by one-pot polymerization among 2,4′-tolylene diisocyanate, isophorone diisocyanate, and poly(oxy-1,4-butanediyl), is achieved through reasonably tuning the hardness of the molecular segment and the strength of the dynamic crosslinking bond. The poly(oxy-1,4-butanediyl) that act as a soft segment can effectively avoid the microphase separation, enabling rapid chain mobility of the polymer at the room temperature. Furthermore, the dual H-bonding from 2,4′-tolylene diisocyanate segment acting as a relatively strong crosslinking bond contributes to high mechanical strength, while the weaker single H-bonding from isophorone diisocyanate segment can efficiently dissipate strain energy by bond rupture, endowing the polymer with rapid room temperature self-healing ability. Featuring state-of-the-art of robust stress strength (≈1.3 MPa), high self-healing efficiency (97% within 6 h), and large tensile strain (≈2100%), the resulting polymers are used for the fabrication of stretchable and self-healable electrical sensor, which can be employed to monitor a variety of physiological activities in real time. The described strategy is promising and universal for healable materials, displaying great potential for developing soft electronics.