Preperation And Study Of Graphene Film Based Flexible Bionic Sensors

With the progress of the manufacturing process of electronic components,wearable electronic devices have realized the transformation from conceptual products to consumer goods,and gradually become a part of human life.Sensors as the core functional components of wearable devices,its research has made significant progress in recent years,not only achieving a breakthrough in performance,but also developing towards flexibility and multi-functional.Especially in the field of a new generation of wearable bionic electronic skin,flexible sensors have the inherent advantages of skin-friendly and easy integration,which attracted the attention of researchers.As an emerging and advanced electronic component,the research on flexible sensor not only needs to optimize the preparation of sensitive materials,but also needs specifical designing of the device assembly method and adaptive circuit according to the requirements in application.It is a comprehensive research field integrating materials,devices and circuit systems.In the research of flexible sensor materials,reduced graphene oxide(rGO)has been widely used in the preparation of sensitive materials for tactile sensors due to its characteristics of high conductivity,lightweight,flexibility and easy modification.However,flexible tactile sensor based on rGO materials have not been applied in large scale at present.The reasons for this phenomenoen on the one hand,such sensors are still in the early stage of research,and previous research results are barely satisfying in complex and harsh environments due to limited performance.On the other hand,some indigenous problems have not been effectively solved in the application of tactile sensors,such as vulnerable to interference,complex peripheral circuits.To sum up,based on the rGO material,this doctoral dissertation has carried out a series of researches on the improvement of sensor performance and the multifunctionalization of sensors for the application of flexible tactile sensors in the fields of biosensing and bionic electronic skin.The specific research content is as follows:(1)Focusing on the high sensitivity along with wide operation range requirements for mimicking the tactile sensing function of human fingertip,the in-situ chemical reduction method has been used to prepare the self-supporting fluffy rGO film(FGF),which shows macroscopic and large-area mound-like fluctuation on the surface and fluffy multi-layered structure in cross-section.Fluffy multilayer structure since the support Fluffy rGO thin film(perspex-walled graphene film,FGF),and further encapsulated FGF into flexible pressure sensor.The results show that the surface morphology and internal structure of the FGF material form a synergistic effect,which enables the sensor to have large contact resistance changing range and structural resistance changing range simultaneously.The pressure sensor shows an excellent comprehensive performance,and realizes a high sensitivity of 10.26 kPa^-1along with a wide operation range upto 200 kPa.Based on this sensor,not only the bionic fingertip tactile sensing function is realized,but also the pulse information of traditional Chinese medicine can be accurately collected.Furthermore,a multi-pixel sensor array based on FGF is prepared,which can cooperate with the circuit system to realize real-time graphical display of pressure and position.(2)In order to further expand the measurement range of pressure sensor to adapt to more complex application environment,a strategy of modification of gel structure by forming strong hydrogen bonds with polyhydroxyl molecules was proposed.The self-assembled Sponge structure rGO aerogel(SGA)was prepared,and further assembled as pressure sensor.The relatively order sponge structure of the SGA allows the sensor to exhibit an extremely wide operation range of up to 1,000 kPa,while simultaneously demonstrating a fast response of 8 ms and impressive durability over 4,000 cycles.The planar pressure phase monitoring system developed based on this sensor can not only recognize the different arch type of the wearer,but also monitor the motion state of the wearer in real time.(3)Aiming at the problem that the traditional pressure sensors are sensitive to external force interference in practical application,a multi-direction force sensor structure was designed based on the collaborative measurement of multiple groups of electrodes.A Flexible graphene aerogel(FGA)film based on rGO and carbon nanotubes was prepared,and further assembled with the Flexible circuit board electrode into the sensor.The results show that the prepared FGA has impressive mechanical and electrical properties,and the honeycomb structure of the FGA contributed to the excellent sensing performance of the assembled sensor,which can achieve the vertical operation range of400 kPa,and has excellent sensitivity linearity in the pressure range of less than 30 kPa.Betterstill,the device has good response and sensitivity to external forces in all directions of the horizontal plane,demonstrating the desired multi-direction force sensing capability that mimics the human tactile function in both vertical and horizontal directions.(4)Based on the real time display and monitoring function of the pressure sensor,a multi-layer fully integrated pressure sensor and electrochromic multi-functional device is proposed,which simplifies the complex peripheral circuit used for pressure display.Combine the high reduction degree rGO film(Graphene film,GF)and carbon conductive tape,a pressure sensor module has been assembled,and shows more than four orders of magnitude of wide resistance change range,as well as upto 300 kPa operation range.The“monolithic”polyaniline electrochromic module has a rapid response of 1.67 s in coloring and 1.05 s in bleaching,and more than 2000 cycles of coloring and bleaching.The assembled multifunctional device not only successfully realizes the function of pressure-controlled coloring and bleaching without peripheral circuit,but also could be further prepared into a multi-pixel electronic skin array device which has good flexibility and individually controllability of each pixel.