Synthesis Of Intrinsic Self-healing/healable Polymeric Materials And Their Multi-functional Applications

After suffering from external injury,organisms can automatically repair or heal the wound without external stimulation.Inspired by this,scientists have developed a series of functional and self-healing/healable polymeric materials with polymeric materials as the main research object.Self-healing/healable polymer can be divided into two categories:extrinsic healable materials and intrinsic healable materials.Compared with the extrinsic healing materials having limited repair times,intrinsic healable materials can realize theoretical infinite repair process through the reversible break-recombination or rapid dynamic exchange of chemical bonds,which is more similar to the healing behavior of organisms.More importantly,various functional and healable materials can be prepared by simply mixing the intrinsic healable materials with some functional fillers.Since such materials can simultaneously repair the mechanical properties and functions,they have gradually become a research hotspot in academia and industry.In this paper,a series of designing strategies are proposed to improve the integrated performance of intrinsic self-healing/healable materials,in order to make them meet the requirements of practical applications.At the same time,they have been applied in different research fields to solve the scientific problems in this field.1.We prepared a novel poly(urea-urethane)-graphitic carbon nitride nanosheets(PUU-g-C₃N₄ NSs)composite material,in which the multiple hydrogen bonds within PUU matrix endow composite material with room temperature self-healing ability,and g-C₃N₄ NSs,serving as both chemical and physical cross-linkers provide composite material with significantly improved mechanical properties.PUU-g-C₃N₄ NSs material was subsequently deposited onto surface of aluminum alloy 2024 as smart anticorrosion coating(AC)by drop-casting method for protection.The anticorrosion performance as well as the self-healing ability of PUU-g-C₃N₄ NSs AC was evaluated by electrochemical impedance spectroscopy,laser microscope and scanning kelvin probe.The experimental results show that PUU-g-C₃N₄ NSs AC maintained its protective capability even after immersion in 0.5 M Na Cl for20 days.Moreover,the artificial scratch on surface of PUU-g-C₃N₄ NSs AC was observed to vanish and the regenerated anticorrosion ability in damage area was gained after healing only 10 min.The introduction of g-C₃N₄ NSs makes PUU-g-C₃N₄ NSs composite material meet the applicable requirements for AC,offers the composite coating excellent anti-penetration ability and retains the satisfactory autonomous self-healing function at ambient conditions,even under high humidity.2.We propose a novel covalent/supramolecular hybrid construction strategy,in which the covalent crosslinks are responsible for providing high modulus and elasticity;while supramolecular crosslinks realize extreme stretchability and rapid self-healing under room temperature depending on the ultrafast exchange kinetics of metal-ligand motifs and multi-coordination modes.The representative polyurea hybrid elastomer,CSH-PPG-Zn-0.25,can be stretched more than 180×its original length with the highest Young's modulus(1.78±0.08MPa)among reported ultra-stretchable materials.CSH-PPG-Zn-0.25 can fully restore mechanical properties of completely cut samples within 3 h.Note that the healing process is able to take place under a low temperature of-20°C and unaffected by surface ageing and atmospheric moisture.Merely tailoring molar ratio of metal/ligand actualizes wide-range tunability of mechanical and dynamic properties,such as Young's modulus(from 1.71±0.08MPa to 5.56±0.22 MPa),maximum tensile strength(from 0.32±0.03 MPa to 4.42±0.23 MPa),strain at break(from>18000%to 630±27%)and storage modulus,ascribing to the increase of crosslinking density and formation of stiff ionic clusters.Based on the different material characteristics,two typical elastomers are respectively employed as flexible and self-healable conductor and self-healable automotive paint.Benefiting from the fantastic anti-ageing and low temperature healing features of CSH-PPG-Zn-0.25,the prepared Ag-NWs/CSH-PPG-Zn-0.25 conductor can even regain its conductive function below zero.CSH-PPG-Zn-0.50 material,meeting mechanical restrict requirements of automotive paints is able to thoroughly eliminate the surface scratches and recover anticorrosion function in local damaged region under atmospheric environment.3.The abundant Zn²⁺-imidazole cross-links were distributed into hydrogen-bonded/Diels-Alder dynamic covalent dual-crosslinked network,resulting in the extraordinary enhancements in mechanical properties and thus obtaining stiff,strong yet tough SCIM,which demonstrates the excellent impact-resistant character under dry condition.Taking advantages of the fact that the reversible destruction/reformation for noncovalent cross-links is influenced by humidity,the SCIM switches from soft/weak to stiff/tough states upon regulating ambient humidity.The experimental results show that the extent of soft-stiff switching ability(E_max/E_min)is high,up to?107.6.The stiff SCIM(E?183 MPa)is able to autonomously restore the mechanical properties during dry-wet cycle and the healing efficiency is high as 85.5%.Moreover,the surface scratches can also be totally healed without leaving any minor scars.Thanks to the synergistic cooperation of dynamic DA covalent bonds,hydrogen bonds and coordination bonds,the SCIM also possess recyclability.4.We describe a novel strategy of multiphase active hydrogen bonds(H-Bonds),toward realizing fast and efficient self-healing at room temperature,even under harsh conditions.The core conception is to incorporate thiourea moieties into microphase-separated polyurea network to form multi-strength H-bonds,which destroy the crystallization of hard do-mains,and at the same time,inserted the dynamic reversible H-bonds in both hard and soft segments,accounting for the surprisingly self-healing performances.The synthesized polymeric material,PDMS-MPI-TM completely recovers all the mechanical properties within 4 h at room temperature after rupture.Significantly,self-healing process can also take place at low temperature(restoration with 85%efficiency in48 h at-20?)or in the water(restoration with 95%efficiency in 4 h).Depending on the cleavage/re-formation of multiphase H-bonds,the material exhibits the unprecedented ultrastrech-ability and notch-insensitiveness.It can be stretched up to 31500%without fracture,and reach notch-insensitive stretching up to 18000%.These exceptional characteristics inspired us to fabricate highly stretchable self-healable underwater conductor and protective self-healing film for suppressing shuttling of polysulfides and preventing crack propagation in S cathode,which provide the pathway for applications in underwater electronic devices or advanced Li-S batteries.5.We designed and synthesized a colorless and transparent glassy polyurethane assembled using low-molecular-weight oligomers carrying a large number of loosely packed weak hydrogen bonds(H-bonds),which has a glass transition temperature(T_g)up to 36.8°C and behaves unprecedentedly robust stiffness with a tensile Young's modulus of 1.56±0.03GPa.Fast room-temperature self-healing was observed in this polymer network that the broken glassy polyurethane(GPU)specimen can recover to a tensile strength up 7.74±0.76MPa after healing for as little as 10 min,which is quite prominent compared to the reported room-temperature self-healing polymers.We revealed that the high density of loose-packed hydrogen bonds can reversibly dissociate/associate below T_g of GPU(that is secondary relaxation),which enables the reconfiguration of the damaged network in the fractured interfaces,in spite of the extremely slow diffusion dynamics of molecular chains under room temperature.Based on these features,we demonstrate that our GPU shows potential application as an optical lens.6.Inspired by the microstructure of dragonfly wings,we show how brittle,stiff,and healable materials can become defect-tolerant by strategies ranging from molecular design to structural processing.Transition metal carbides/carbonitrides form an interconnected mechanical framework,similar to the rigid nervure in dragonfly wings to stabilize the growth and slow down the extension of the crack,while the initially glassy healing polymer closely bonds to the rigid framework through powerful interfacial supramolecular interactions,playing the key role of the soft membrane dissipating stress-energy.Compared to initial polymers,the obtained dragonfly wing-inspired SP/MXene nanocomposite(SPM)exhibits an increase in fracture toughness and flexural strength(54.3-and 25.0-fold,respectively),exceptional thermal stability,mechanical and functional repairability,and good electromagnetic interference shielding function.These properties considerably broaden the practical application of healable polymers in harsh conditions.