Preparation And Properties Of Graphene Flexible Strainsensing Materials

In recent years,graphene sensing composites have been widely applied in strain sensors.In particular,with the development of science and technology,the advent of wearable devices,flexible screens,robot electronic skin,and flexible strain sensors has become increasingly demanding for sensing materials.The flexible strain-sensing material as an important part of the strain sensor is the key to monitor stress and strain.The principle of strain-sensing materials is that the change of the structure after the deformation of the material leads to a change in the resistance,and the resistance returns to its original state after the stress is removed.Traditional graphene/polymer flexible strain-sensing materials?especially bulk aerogels?introduce a large amount of flexible polymers,so it is difficult to balance the elasticity and conductivity.In addition,the compression anti-fatigue of the material?the number of compression cycles?and the electrical signal stability of the sensing materials also need to be improved.In terms of bending sensing,sensing materials with high bending sensitivity,high conductivity?low driving voltage?and bending stability are still difficult to produce.In this thesis,graphite oxide with the oxygen content of 47.11 wt%?the mass ratio of carbon to oxygen was 1.03?was prepared by chemical oxidation.The graphite oxide containing a large number of hydroxyl groups,carboxyl groups and epoxy groups can be uniform Ly dispersed in deionized water by ultrasonication.Finally,the prepared graphene oxide?GO?sheets were almost within 6 layers.Then,before preparing the graphene/carboxymethylcellulose?GE/CMC?compressive strain-sensing aerogel,we first determined the concentration of the GO aqueous solution to be5 mg/mL by zeta potential analysis and aerogels'morphology.By controlling the amount of CMC,the flexibility and pore structure of the composite aerogels were changed.After reduction with hydrazine vapor,GE/CMC-2 conductive aerogels with uniform and compact pore structure and good compression resilience were selected to test compressive sensing performance.The results show that the electrical conductivity of GE/CMC-2 aerogels at 70%compressive strain is 86.73 S/m.And after thousands of fatigue compression tests,the conductivity value of GE/CMC-2 is still relatively stable.After 4000 cycles of 50%strain compression test,the relative resistance signal curve of GE/CMC-2 is regular,and there is no obvious deformation.At 70%compressive strain,the gauge factor of GE/CMC-2 GF can reach 1.58.However,the flexural signal response and repeatability of the stripe GE/CMC-2 aerogels still need to be improved.In order to improve the bending strain-sensing response of sensing materials,we used a vacuum filtration self-assembly method to prepare GE/CMC composite films,and the GE/CMC film was coated with a layer of 1 mm thick silicone rubber to improve the bending flexibility.And we optimized GO concentration?3 mg/mL?and reducing conditions?hydroiodic acid at70?for 60 min?.The results show that the bending signal response of GE/CMC-30 is regular,and the current response is obvious at a low voltage of 1 mV,and the conductivity of GE/CMC-30 is 1321.9 S/m.The bending-strain sensitivity of GE/CMC-30 composite films at 90°positive bending is as high as 0.83 rad^-1.The response time of GE/CMC-30 at 90°positive bending is less than 190 ms.The current signals of films during bending can be converted into resistance signals under constant voltage,and it can be linearly fitted to the relationship between the relative resistance?R/R₀?and the bending angle???.The approximate bending angle can be derived from the relative resistance value according to the fitting formula.In 500 cycles of positive bending test?0-90°?,GE/CMC-30 has stable bending signal response.