Study On High Strength And Toughness Autonomically Self-healing PDMS Elastomers Based On Multiple Dynamic Bonds

Polydimethylsiloxane(PDMS)has many excellent physical and chemical properties,and has been widely used in high-tech fields such as military industry,aerospace and artificial intelligence.However,it is inevitable to cause damage in the service process,which will seriously affect the stability and safety of materials.In order to solve this problem,researchers introduced the concept of self-healing into PDMS to repair the damage timely and ensure the safety and stability of materials in service.At the same time,it can also prolong the service life of materials,reduce the waste of resources and relieve the pressure for the environment,which is of great significance to the sustainable development of materials.Self-healing materials has two important problems:1.the materials for the excellent comprehensive mechanical properties required for the stability of the molecular structure and get the self-healing abilities required of the dynamic characteristics of the molecular chain of contradiction between,lead to the comprehensive mechanics performance of the self-healing polymer at room temperature are often low(high strength but toughness is low,good toughness but low strength).2.The healing process often needs the help of external stimuli(heat,light,solvent,etc.)to complete,and these conditions are difficult to obtain in the practical application of materials.In order to solve these problems,by designing the molecular structure,crosslinking network structure and microphysical structure of PDMS,this paper successfully prepared the high strength and toughness room temperature non-disturbance self-healing PDMS elastomer,studied its structure,mechanical properties and self-healing properties,and preliminarily explored its self-healing mechanism.In this study,the molecular structure of PDMS was designed,and a side group Co/pyridine coordination cross-linked PDMS elastomer(Py-PDMS-Co)was successfully prepared.The effects of cross-linking density and central atom on its mechanical properties and self-healing properties were studied.The breaking strength of Py-PDMS-Co is 0.13 MPa,and the healing rate is 91%after 24 h at room temperature in air.Compared with the structure of the dynamic bond in the molecular backbone(healing temperature is 120 ^oC),side-chain dynamic bond cross-linked elastomer can not only improve the reversibility of dynamic bond by taking advantage of the large activity space of side groups,but also avoid the introduction of rigid groups in dynamic bond into the main chain and the increase of main chain molecule weight of PDMS,maintain the good movement performance of molecular chain,and obtain excellent healing ability.However,the mechanical properties of the Py-PDMS-Co is low.In order to obtain a room temperature self-healing PDMS elastomer with excellent comprehensive mechanical properties,a PDMS cross-linked network was designed based on the molecular structure of side group dynamic bond cross-linked PDMS,and a boroxine,B-N coordination and hydrogen bond multiple cross-linked PDMS elastomer(PDMS-BN)was successfully prepared.The maximum strength of PDMS-BN is 1.72 MPa,the elongation is307%,the toughness is 4.92 MJ m^-3,and the healing rate is 91%after 48 h at room temperature in air.Compared with a single cross-linked elastomer,multiple cross-linked elastomers with"sacrifice bond"can be constructed by introducing dynamic bonds of different strength into PDMS network,which can ensure the strength of the material by using B-O strong bond(bond energy 809 k J/mol)stable cross-linked network.In addition,the weak bond(B-N coordination,hydrogen bond)can be used to dissipate a lot of energy to improve the toughness and elongation of the elastomer,and the excellent comprehensive mechanical properties are obtained.B-N coordination can not only act as a"sacrifice bond",but also improve the dynamics activity of boroxine,which can make the elastomer healing at room temperature without external stimuli.In order to further improve the mechanical properties and healing properties of room temperature self-healing PDMS elastomer,based on the side group dynamic bond cross-linked PDMS structure and strong and weak bond multiple cross-linked PDMS network structure,the microphysical structure of the elastomer was designed,and a strong and weak hydrogen bond multiple cross-linked PDMS elastomer(PDMS-UPy-Urea)was successfully prepared.The strength of PDMS-UPy-Urea elastomer is 2.35 MPa,the elongation at break is 394%,and the toughness is 8.00 MJ m^-3(the healing rate is 94%after 24 h at room temperature;the healing rate reached 91%after 20 min at 80?).A PDMS elastomer with microphase separation and multiple hydrogen bond crosslinking was constructed by introducing UPy group which is easy to aggregate into hard phase structure and Urea group forming weak hydrogen bond in the side group of PDMS.The hard phase was not only used to strengthen the PDMS elastomer,but also the cooperative effect of strong and weak bonds was used to improve the mechanical properties and repair properties of the elastomer.In this study,a series of high strength and toughness room temperature non-interference self-healing PDMS elastomers were prepared through the design of PDMS molecular structure,cross-linking network structure and microphysical structure,which solved two important problems existing in self-healing materials and provided important ideas and theoretical guidance for the preparation of ultra-high strength and toughness self-healing silicone rubber.