| Self-healing polymeric material is a kind of smart polymer that can repair damage of themselves automatically or via external simulations.Self-healing polymeric material has received extensive attentions because they can decrease maintenance costs and improve product safety,lifetime,and reliability.Recent years,various strategies have been developed to fabricate healable materials that restore their structures,mechanical properties,and functions.However,self-healing polymeric materials still face some problems to solve when they are used in the practical application:?1?to solve the conflict between enhancing the mechanical robustness and improving the healability.?2?to further extend the applications of self-healing polymeric materials in wider application areas;?3?to develop a simple,convenient,and widely applicable strategy for the large-scale fabrication of self-healing materials.Based on the above problems,we carried out the following three aspects of research work.1.Mechanically robust self-healing shape-memory polymeric films that can heal the mechanical damage and the fatigued shape-memory function in the presence of water are fabricated by layer-by-layer assembly of branched poly-?ethylenimine??b PEI?-graphene oxide?GO?complexes with poly?acrylic acid??PAA?.The free-standing(PAA/b PEI-GO0.02)*35 films made of b PEI-GO complexes with a mass ratio of 0.02 between GO nanosheets and b PEI are mechanically robust with a Young's modulus of 19.8±2.1 GPa and a hardness of 0.92±0.15 GPa.And the(PAA/b PEI-GO0.02)*35 films also exhibit excellent humidity-induced shape-memory functions,they can reach an?100%shape-recovery ratio during long-term usage.The(PAA/b PEI-GO0.02)*35 film became fatigued with the total recovery ratio declines after repeated shape memory cycles.However,the shape-recovery ratio of the(PAA/b PEI-GO0.02)*35 films returns to?100%after the films being immersed in water for 30 min.In the meanwhile,the(PAA/b PEI-GO0.02)*35 films also have highly efficient healability that they can heal cuts with a width of several tens of microns penetrating through the entire film in the presence of water.And the mechanical properties of the films can also be restored to the original ones after healing.The integration of healing function into(PAA/b PEI-GO0.02)*35 shape memory films significantly enhances their durability and enables their repeated usage in a precise way.As far as we know,this is the first fabrication of shape-memory films that can simultaneously heal mechanical damage and fatigued shape-memory function.2.Branched poly?ethylenimine??b PEI?grafted with ferrocene groups?Fc??denoted as b PEI-Fc?can complex with reduced graphene oxide?RGO?modified with?-cyclodextrin?CD??denoted as RGO-CD?in solution based on host-guest interactions to form b PEI-Fc&RGO-CD complexes.The as-repaired b PEI-Fc&RGO-CD complexes werse then Lb L assembled with PAA to fabricate PAA/b PEI-Fc&RGO-CD composite films that exhibited both excellent mechanical properties and rapid and highly-efficient self-healing properties.When the mass ratio between RGO-CD and b PEI-Fc was 0.04,the(PAA/b PEI-Fc&RGO-CD0.04)*45 films were mechanically robust and had the a Young's modulus of 17.2±1.9 GPa and a hardness of 1.00±0.30 GPa.When the damaged(PAA/b PEI-Fc&RGO-CD0.04)*45films were dipped in H2O2,the host-guest interactions between RGO-CD nanosheets and the matrix PAA/b PEI-Fc films can be broken.Thus,the(PAA/b PEI-Fc&RGO-CD0.04)*45 films can be reversibly and highly efficiently healed.After that,the host-guest interactions between RGO-CD nanosheets and the films were rebuilt in glutathione?GSH?solution,which enabled the fully restoration of the original mechanical robustness of the(PAA/b PEI-Fc&RGO-CD0.04)*45 films.The introduction of reversible host-guest interactions between nanofillers and polymeric films was for the first time proposed to effectively solve the conflict between highly efficient healing capability and excellent mechanical robustness.3.1-ethyl-3-methylimidazolium acetate?EO?is introduced into the complex solution of Nafion and polyvinyl alcohol?PVA?to form homogeneous and uniform Nafion-PVA-EO complex solutions based on the hydrogen-bonding interactions between Nafion and PVA.The self-healing and recyclable Nafion-PVA-EO ionogels which simultaneously exhibit high mechanical strength and high stretchability can be prepared by a simple casting method.Tensile tests show that the Nafion-PVA-EO ionogels possess excellent mechanical properties with mechanical strength,elongation at break and toughness being?2.6 MPa,?1024.2%,?14.0 MJ/m3,respectively.The rheological test proves that the storage modulus of the Nafion-PVA-EO ionogels is higher than their loss modulus below 130?,demonstrating the ionogels have good thermal stability.The Nafion-PVA-EO ionogels have good conductivity and their conductivity at room temperature is 2×10-3 S/cm.Originating from the dynamic nature of hydrogen-bonding interactions,Nafion-PVA-EO ionogels can heal mechanical damage at 70?and be remolded at 90?.The healed and recycled ionogels regain their mechanical strength.The Nafion-PVA-EO ionogels exhibit good sensing performance,showing sensitive and stable response to deformation and humidity changes of environment.The Nafion-PVA-EO ionogels are expected to be used as a wearable sensor to detect human movement and respiration. |
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