Healable And Mechanically Strong Polymeric Materials Based On Polymeric Complexes

Polymeric materials are prevalent in almost every facet of human activities in the modern society because of their merits of light weight and low cost.However,the mechanical strength of polymeric materials is much lower than inorganic materials.Polymeric materials suffer from mechanical damage,which severly decrease their mechanical properties and largely reduce their service life.Enhancing the mechanical strength of the polymeric materials can improve the damage tolerance and stability of the materials.Moreover,endowing polymeric materials with self-healing properties will further prolong their service life and improve their reliability.The introduction of non-covalent interactions and dynamic covalent bonds can impart self-healing properties into polymeric materials.The healing properties of polymeric materials largely depend on highly reversible non-covalent interactions and dynamic covalent bonds as well as the high mobility of polymer chains.However,self-healing/healable polymeric materials featuring these two characters usually exhibit weak mechanical strength.Therefore,it is challenging to farbicate polymer materials simultaneously possessing high mechanical strength and excellent healing properties.To solve the above problems,we carried out the following studies:1.We report the fabrication of mechanically strong polymer composites with excellent healing capacity by the complexation of polyacrylic acid(PAA)with polyvinylpyrrolidone(PVPON)in aqueous solution followed by molding into desired shapes.The coiled PVPON can complex with PAA in water via hydrogen-bonding interactions to produce transparent PAA–PVPON composites homogenously dispersed with nanoparticles of PAA–PVPON complexes.As healable materials,the PAA–PVPON composite materials exhibit a strong mechanical strength,with a tensile strength of?81 MPa and a Young's modulus of?4.5 GPa.The superhigh mechanical strength of the PAA–PVPON composite materials originates from the highly dense hydrogen bonds between PAA and PVPON and the reinforcement of in situ formed PAA–PVPON nanoparticles.The reversibility of the relatively weak but dense hydrogen bonds enables convenient healing of the mechanically strong PAA–PVPON composite materials from physical damage to restore their original mechanical strength.The PAA-PVPON composites are stable in water because of the hydrophobic interactions among pyrrolidone groups.2.We demonstrate the fabrication of healable hydrogels with high mechanical strength and damage-tolerant ability by complexation of PAA and citric acid-ethylenediamine carbon dots(CDs)mixtures with PVPON in aqueous solutions.The introduction of CDs can significantly improve the mechanical strength,strain,and toughness of PAA-PVPON hydrogels.With the addition of CD fraction of 15 wt%,the PAA-PVPON-CDs hydrogels exhibit the most outstanding mechanical properties with a mechanical strength,strain,and toughness of?5.2 MPa,?770%,and?118.5 MJ m^-3,respectively.These values are 1.58,1.51,and 2.39 times higher than those of PAA-PVPON hydrogels,respectively.Moreover,the PAA-PVPON-CDs hydrogels exhibit excellent damage tolerance with a high fracture energy of?52.8 k J m^-2.The high mechanical strength and excellent damage tolerance of PAA-PVPON-CDs hydrogels originate from the high density of supramolecular interactions between CDs and polymer matrices and the deformable properties of CDs.More importantly,the fractured hydrogels can heal themselves under the assistance of water at?45°C,originating from the reversibility of the supramolecular interactions among PAA,PVPON and CDs.3.We report the fabrication of healable elastomers with high mechanical strength and stretchability by complexation of PAA and metronidazole CDs(MCDs)mixtures with polyethylene oxide(PEO)in aqueous solutions.The mechanical strength of PAA-PEO elastomers increases with the increasing molecular weight of PEO,while their strain decreases with the increasing molecular weight of PEO.PAA-PEO elastomers with high molecular weight of PEO(Mw ca.600 000)have the highest mechanical strength of?22.3 MPa and a strain at break of?840%.The introduction of MCDs can improve the mechanical strength and strain of PAA-PEO elastomers.The PAA-PEO-MCDs elastomers with a MCD fraction of 15 wt%possess a high mechanical strength of?35.5 MPa and strain at break of?1080%.MCDs can serve as nanofillers to increase crosslinking density of PAA-PEO-MCDs elastomers and enhance their mechanical strength.In addition,MCDs can deform under external force,which can impart high extensibility to the elastomers.More importantly,originating from dynamic nature of supramolecular interactions in PAA-PEO-MCDs elastomers,the elastomers are capable of healing from physical damages at room temperature and a releative humidity of 98%.