Preparation And Electrical Properties Of PEDOT-based Self-healing Films Relying On Diels-alder Reaction

Intrinsical self-healing,as a bionic technology,can realize self-healing of cracks in materials or devices to ensure their safety and prolong their life.Therefore,the combination of this technology and electrical properties of materials has attracted more and more attention in the field of inorganic or organic electronics.At present,the preparation of conductive self-healing materials is mainly based on the combination of intrinsic self-healing polymers and inorganic conductive fillers.How to realize the effective compatibility between the various composite unit materials,the synergy of the conductivity and self-healing of the composite system,and the mild self-healing conditions have been the core and urgent problems to be solved in this field.Poly(3,4-ethylenedioxythiophene)(PEDOT)and its derivatives,as a series of the most successful conducting polymers(CPs),have attracted much attention in the field of conductive self-healing due to their tunable conductivity,good biocompatibility,thermal stability and environmental stability.In view of the research of PEDOT self-healing,the commercial poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PEDOT:PSS)aqueous dispersion(especially the high conductivity Clevios PH1000)is mainly used as the research object.The self-healing is realized by water-driven swelling of PSS~-chain or adding some surfactants,cross-linked biomolecules or other additives to improve the viscoelasticity of composites.Although these composites exhibit good machinability and electrical conductivity,they must be repaired by water drive,which will greatly limit the application of these materials in electronic devices.In addition,the monopoly single source,high cost and difficult storage of Clevios PH1000 will also limit its large-scale use,and the excessive polyanion PSS~-has strong acidity and moisture absorption,which is also a fatal problem for electronic devices.In order to overcome the above challenges,the reversible Diels-Alder(DA)bond was introduced into PEDOT:PSS and PEDOT systems to prepare conductive polymer films with thermal repair properties.The effects of different factors on the properties of the films(morphology,conductivity,surface wettability,self-healing,etc.)were systematically explored.1.In order to introduce self-healing function into the existing conductive polymer system with excellent application effect,a series of PEDOT:PSS/DA composite films were prepared by physical blending with small molecular monomers with DA group(furan(Fu)and maleimide(MI))in PEDOT:PSS system.The effects of the proportion of DA small molecules,the type and proportion of conductive accelerators(dimethyl sulfoxide(DMSO)and isopropyl alcohol(IPA))and dry film temperature on the morphology,conductivity,surface wettability and self-healing performance were investigated.The results showed that the increase in the proportion of DMSO and IPA did not play a strong role in promoting the thermal repair of the film,and as the proportion of additives increased to a certain extent,the fluidity of the composite system increased and it was difficult to form a film.With the increase of DA monomer ratio,the thermal repair performance of the film was not greatly affected,but the white crystalline substances precipitated on the film surface increased.The drying temperature has little effect on the thermal recovery,but the annealing treatment will make the film smoother.Therefore,the blending of PEDOT:PSS and DA monomers(Fu and MI)cannot achieve effective film thermal repair.This may be due to the strong acidic system caused by excessive PSS~-and the insufficient bonding of small molecule DA compounds.2.In order to avoid the adverse effects of PSS~-acidity and hygroscopicity on the self-healing ability and future application needs of CPs,a series of intrinsic self-healing polymer polyurethane(PU-DA)with DA group but not water-soluble was synthesized,and then a series of PEDOT/PU-DA composite films were prepared by direct introduction of 3,4-ethylenedioxythiophene(EDOT)monomer and iron p-toluenesulfonate(oxidant)into the solution by in-situ oxidative polymerization.The effects of the ratio of PU-DA and the oxidative polymerization time of EDOT on the morphology,conductivity,surface wettability and self-healing properties of the composite films were investigated.The results showed that when the concentration of PU-DA tetrahydrofuran(THF)solution was 30 wt.%,the prepared composite film could achieve effective synergy of conductivity and self-healing.With the extension of EDOT oxidation polymerization time,the conductivity of the composite film will gradually decrease.With the increase of thermal repair temperature,the structural repair effect of the film will gradually increase,but the conductivity will be lost.3.In order to further enhance the self-healing ability of the conductive film,the small molecule compound 2,4-hexanediyne-1,6-diol(DADOL)with DA group was introduced into the PU-DA macromolecular system,and the PU-DA/DADOL mixed solution was prepared by simple mechanical blending.Then,a series of PEDOT/PU-DA/DADOL composite films were prepared by in-situ oxidative polymerization by directly introducing EDOT monomer and iron p-toluenesulfonate(oxidant)into the solution.The effects of the ratio of DADOL to DMSO on the morphology,conductivity,surface wettability and self-healing properties were investigated.The results show that the reversible multiple DA bonding can make the composite film achieve the simultaneous repair of structural morphology and electrical conductivity under thermal driving.The key is to optimize the composition ratio of the composite system,and regulate the thermal driving process from 100°C to 60°C to ensure the reverse DA(r-DA)reaction and the re-formation of DA bonds.The crosslinking reaction of DA in the film is caused by co-existing macromolecule PU-DA and small molecule DADOL.Among them,the composite film prepared with5 wt.%DADOL had the highest conductivity without DMSO,and its bulk resistance was 0.89±0.11 MΩ.The composite film was treated at 100°C for 10 min,and then treated at 60°C for 6 h to achieve the repair of cracks at the damage site and the restoration of electrical properties.