Design,Synthesis,and Applications Of Autonomously Ultrafast Self-Healing Materials

Inspired by the autonomous intrinsic self-healing ability of biological organisms in the natural world,artificial smart self-healing systems using both physical and chemical approaches have been extensively designed in recent years,which can efficiently extend the life spans of existing functional materials.Generally,the microcracks generated during the long-term usage of materials will rapidly expand into macroscopic damage,which are difficult to self-heal.Therefore,it is highly significant to develop ultrafast self-healing systems from the perspective of practical application.By systematically exploring the internal healing mechanism of different types self-healing materials,we not only successfully designed and fabricated a series of novel self-healing materials which can spontaneously and rapidly self-heal at room temperature without any external stimulation,but also demonstrated their potential applications in various fields.The achieved research findings are listed as follows:1.By selecting coordination bonds with highly tunable bond energies and dynamics as the research object,taking the profound understanding of"structure-property relationship"between micro-coordination structure and macro-healing property as the starting point,a kind of ultrafast self-healing material at room temperature based on dynamic coordination bonds was successfully developed.Firstly,four different Zn(II)-diiminopyridine coordination model complexes with same coordination configuration but modified by different substituents(-H or-CH₃)were synthesized.The dynamic exchange behavior of small molecule complexes was monitored and studied by high resolution mass spectrometry.Then,different Zn(II)-diiminopyridine coordination complexes were introduced into the linear polydimethylsiloxane(PDMS)polymer chain by imine polycondensation,resulting in two novel metallopolymer networks denoted as PDMS-NNN-Zn and PDMS-Me NNN-Zn,respectively.Based on the results of isothermal titration calorimetry,dynamic rheological analysis and tensile tests,we demonstrated that two crosslinked Zn(II)-diiminopyridine complexes were similar in coordination numbers and geometries,but differ in coordination bond energy and bond dynamics.The coordination bond in PDMS-Me NNN-Zn polymer was weaker but more dynamic.Consequently,PDMS-Me NNN-Zn polymer had higher stretchability and better self-healing properties.The inflicted cracks and mechanical properties on PDMS-Me NNN-Zn polymer films can be completely healed after healing at room temperature for only 30 min with average healing efficiency as high as 94.7%.2.Providing that the existing self-healing materials based on dynamic imine bond can not achieve spontaneous and rapid healing at room temperature,herein,by introducing trace amino to catalyze imine exchange and metathesis reaction,an ultrafast self-healing polyimine was successfully obtained.Firstly,we utilized ¹H-NMR to demonstrate the dynamic exchange rate of Schiff base in solution can be significantly increased in the presence of trace amino groups.Furthermore,the target polyimine material(BTA-PDMS)was synthesized via aldimine polycondensation reaction of[1,1'-Biphenyl]-3,3',5,5'-tetracarboxaldehyde(BTA)with a few excess of amino terminated polymethylsiloxane(H₂N-PDMS-NH₂).Compared with the control sample,it was proved that the catalytic effect of trace unreacted amino groups in the polyimine crosslinking network could accelerate the exchange rate of dynamic imine bonds.After being destroyed in different ways(cut,scratched and punctured),the surface wound of BTA-PDMS could self-heal spontaneously within 10 s,and the mechanical properties could recover to the initial state within 60 s.The corresponding self-healing efficiency was dertemined to be 99.3±4.6%.Owing to the unique ultrafast self-healing capability and excellent adhesion strength on different substrates(glasses,metals,Teflon and plastics),BTA-PDMS was successfully applied in the field of self-healing adhesives and waterproof sealants.3.Because of the dynamic nature of most self-healing materials based on dynamic chemical bonds,it is difficult for them to withstand the interference of external harsh conditions during the long-term usage process.How to maintain the rapid healing performance as well as further improve the stability and self-healing capcity in a variety of environments has great significance.By selecting the high molecular weight PDMS with excellent environmental stability as the backbone and using the one pot polycondensation reaction between amino and isocyanate,a small amount of urea bond unit(0.26 wt%)was introduced to induce higher density of polymer chain entanglements and the self-healing polymer network HPUrea crosslinked by high-density physical reversible entanglement interaction was successfully obtained.The as-synthesized polymers not only exhibited ultrafast self-healing capabilities at ambient conditions,but also can maintain its long-term stability and rapid self-healing ability under a variety of harsh environments,including aqueous solutions,saturated brine,silicone oil,organic solvents,strong acid,strong alkali,freezing temprature and redox agents.After healing for 30 min at room temperature without any intervention,the highest self-healing effiecieny of HPUrea was calculated to be 97.6±3.6%.Moreover,this polymer could be easily integrated with Eutectic Gallium-Indium(EGa In)alloy to achieve layer-by-layer self-healing electronic skin sensors,which realized the real-time recording,monitoring and regulation of human activities.