The Preparation And Study On Mechanical Properties Of Graphene Based Flexible Composites Film

The force sensor is a kind of electronic device that can convert the complex mechanical physical quantities into usable output signals according to a certain rule.The performance and application of the force sensitive sensor mainly dependson the sensitive materials,which include semiconductor,metal and synthetic materials,carbon materials.Among them,graphene has excellent mechanical properties due to its unique two-dimensional structure and excellent crystal quality.The specific mobility of graphene at room temperature is as high as 15,000 cm ~2/(V.s),the specific surface area is 2630 m~2/g,and the Young's modulus and mechanical properties are 1.02 TPa and 130GPa,respectively.In addition,it can withstand more than 20%strain.Therefore,graphene-based flexible composite films were prepared by using graphene as sensitive materials and their mechanical properties were also studied.The main work of this paper is as follows:(1)The naturally viscous material polyethylenimine(PEI)and graphene oxide(GO)were used to fabricate composite films by facile chemical layer-by-layer self-assembly(CLS)methods,then films were transfered from glass substrate to flexible Polydimethylsiloxane(PDMS)substrate by using the stickiness of PDMS.Finally,the PEI-rGO/PDMS composite films were fabricated by thermal reduction method.At the same time,the optimum device parameters were optimized by controlling the self-assembly layers of composite film and the concentration of graphene oxide in self-assembly growth process.The optimal sensor obtained a remarkable performance with a high gauge factor(754 under 5%stretch deformation)and an ultralow limit of detection(0.1%strain).A linear relationship between the normalized response of the sensors and the stretch deformation were observed in the low strain range.The proposed sensor achieved durable properties after 500 stretching-relaxing cycles and could work and withstand a strain up to 50%.In addition,combined with characterization test and strain test results that show the high response of the graphene-based strain sensor mainly comes from the tunneling effect between graphene sheets.When the graphene conductive network was broken under strain,the resistance of the graphene-based composite film was increased sharply.(2)The poly(vinylidene fluoride-co-hexafluropropylene)(PVDF-HFP)is a polymer piezoelectric material with excellent flexibility and hydrophobicity.However,the piezoelectric properties and mechanical properties of PVDF-HFP material are not excellent.A large number of studies have shown that the mechanical properties of the polymer material could be effectively enhanced by adding a small amount of nanoparticlesintothepolymer,andthenewmaterialwouldbe endowed with special functions.In this paper,PVDF-HFP/GO composite thin films were prepared by casting method and the nanometer graphene oxide was as filler material.At the same time,the optimum matching parameters were optimized by controlling the mass fraction of graphene oxide.The experimental results showed that the crystallinity of PVDF-HFP composite film with 0.05wt%graphene oxide was obviously improved,and the content of?-phase in the film after uniaxial stretching of the composite film was greatly improved(From 20%to 92%).In addition,combined with the characterization test and experimental test results show that the excellent mechanical properties and specific surface area of graphene oxide and the excellent compatibility with PVDF-HFP materials are the key factors to improve the stress transfer efficiency of the interface.It makes the composite film crystallinity and mechanical properties have been greatly improved,and the piezoelectric properties are further enhanced.