Research On Flexible Strain Sensor Based On Graphene

The carbon atoms of graphene are bonded together to form a honeycomb lattice structure through ? bond.The two-dimensional layered nanostructure makes it outstanding in electrical,mechanical,thermal,and optical properties,in specific,excellent electron mobility at room temperature,Young's modulus up to 1 TPA,breaking strength of 130 GPA,ultra-high thermal conductivity,and 97.7% light transmittance.Preparation methods and applications of graphenebased material have become study hotspots in the 21 st century.And graphene has made remarkable achievements in the research of new micro-nano electronic devices,batteries,and flexible sensors.However,the problems of complex preparation process and small tensile range of graphene still remain and have hindered its commercialization.Oriented by flexible stress sensor studies,the thesis prepared graphene with improved Hummers method.Then,flexible sensitive layer,capacitive and piezoresistive stress sensor were fabricated.The sensing performance and sensing mechanism were discussed.Main studies and results show as follows:First,the flake graphite powder was utilized to prepare reduced graphene oxide.The graphite was oxidized by concentrated sulfuric acid and potassium permanganate.We analyzed the crystal structure,micro morphology,molecular vibration and lattice vibration of the products,and concluded that the lattice structure of graphene oxide(GO)differs from that of graphite,and that the products obtain a certain number of defects.After reduced by hydrazine hydrate,the reduced graphene oxide(r GO)formed a uniform suspension and was evenly dispersed in water.The number of graphene layers was about 8,which contained defects in lattice structure.Second,we prepared a capacitive sensor based on r GO.The r GO layer was used as the series connection of two capacitors,one of which has hollow structure.The performance of contact sensing and bending sensing was greatly improved due to its special structure.Third,we blended polyvinyl alcohol(PVA)solution with r GO aqueous solution and dried the blend under atmospheric pressure.We obtained a flexible and conductive micron-scale layered material by this one-step method.The best mass fraction of r GO in the composite film was 20%.The strength and stress sensing tests revealed that the sensor has good conductive stability in static state,and that the sensing detect range varies from 90°to-90 °,the gauge factor reaches to 0.96,and sensing stability is more than 100 cycles in dynamic sensing.