Research On The Electrical Properties Of Graphene Flexible Devices Via Direct Writing Printing

Flexible sensor has the advantages of high sensitivity,good flexibility,light weight,easy integration and wearability,which makes it have great application prospects in the field of personal health monitoring.On the other hand,the two-dimensional nanomaterial graphene has excellent thermal,electrical and mechanical properties and can be assembled into various structures,such as graphene fibers,graphene ribbons,graphene films and graphene aerogels.Therefore,graphene-based flexible sensing devices are expected to become human activity assessment and personal health monitoring devices.In this thesis,based on the synthesis of graphene oxide ink,a series of researches on the preparation and properties of patterned graphene flexible circuit,integrated graphene strain sensor and graphene electrochemical multi-analysis sensor are carried out by using direct writing printing technology.The main contents are shown as follows:The graphene oxide was prepared by the modified Hummers method.The scanning electron microscopy(SEIM),atomic force microscopy(AFIM),X-ray diffractometer(XRD),and Fourier transform infrared spectroscopy(FT-IR)results showed that graphene oxide was prepared with the lateral size of 20-40 ?m,thickness of 0.98 nm and containing more oxygen-containing functional groups.Then the graphene oxide dispersion was concentrated into 20 mg/mL as the ink.The graphene oxide ink was printed on glass,silicon wafer,polyethylene terephthalate(PET),polydimethylsiloxane(PDMS)and other rigid and flexible substrates by direct writing printing technology,and the patterns were reduced by hydroiodic acid.The electrical conductivity of the reduced patterns were measured to be 4.21 × 104 S/m.In addition,the Raman spectroscopy(Raman),X-ray diffractometer(XRD)and X-ray photoelectron spectroscopy(XPS)characterization tests of the graphene oxide before and after reduction showed that oxygen-containing functional groups decreased significantly after reduction,and the electrical properties of reduced graphene oxide have been restored.LED lights were connected by the reduced graphene oxide circuit,and the LED lights were lit when 3 V voltage was applied,indicating that the graphene flexible circuit had good electrical property.Subsequently,the layered stacked graphene ribbons and the dense porous graphene aerogels were prepared by direct drying and freeze-drying method.The linear,wavy graphene ribbons and linear,wavy,serpentine graphene aerogels were tested the relative change rate of resistance in compression,bending,torsion,stagger,tensile and cycle stability.The results showed that the electrical signal of graphene ribbons were relatively stable and the resistance almost unchanged,while the resistance change rate of graphene aerogels were high,and the electrical response of serpentine graphene aerogel was the most sensitive among all the samples.Based on the different microstructures and macroscopic patterns of the graphene ribbons and the graphene aerogels in electrical sensitivity,the flexible graphene sensor was composed of the wavy graphene ribbon and the serpentine graphene aerogel.Next,a multi-channel electronic data logger was used for point recognition and wrist motion monitoring of the patterned graphene sensors.The results showed that the sensor had different responses to the motion of each point and wrist joint.Data statistical analysis software Minitab 16 and SYSTAT 12 were used to carry out principal component analysis(PCA),hierarchical clustering analysis(HCA)and linear discriminant analysis(LDA)for resistance changes of different motions,which realized point identification and multi-analysis sensor monitoring of wrist movement.Based on the differences in the electrical sensitivity of graphene materials with different microstructures,and combined with the electrochemical sensing property of graphene-based materials,the electrochemical property of different microstructures graphene materials were studied.With the different conductivity and adsorption properties of the layered stacked graphene film and the dense porous graphene aerogel,graphene film and graphene aerogel electrode were prepared respectively.A standard three-electrode system with platinum as the counter electrode and Ag/AgCI as the reference electrode were selected for electrochemical tests.Differential pulse voltammetry and cyclic voltammetry were used for electrochemical detection and analysis ofcations,anions,amino acids,amines,sugars,etc.Then,multi-data analysis was carried out by using three data analysis methods of PCA,HCA and LDA.The results showed that the two microstructure electrodes can identify and effectively classify each substance under the interaction of the two microstructure electrodes.In addition,the device also achieved the resolution of the anion and cations of different concentration gradients and the mixture of seven different types.The introduction of graphene electrodes with different microstructures provides an effective way for the analysis of complex body fluids.