Preparation And Properties Of MXene/AgNWs Flexible Sensor

With the rapid development of the air transport industry,the transport volume continues to increase,and the phenomenon of overnight overtime work and overtime work is more and more common.The health of the aircraft personnel is directly related to the flight safety of the aircraft.On the other hand,the aircraft also has to bear complex and long-term fatigue load,unexpected impact load and other effects during operation,and its health condition directly determines the flight safety of the aircraft.Therefore,it is very necessary to conduct real-time health monitoring on the crew and aircraft structure to ensure the safety of aircraft service.In recent years,with the rapid development of flexible conductive materials,the application potential of flexible sensors based on these materials in wearable electronic products has aroused wide attention.The research and development of highly sensitive flexible sensors can not only be used for real-time monitoring of aircraft personnel,but also can be used for real-time health monitoring of important aircraft structures,to further ensure the flight safety of aircraft.In this thesis,one-dimensional silver nanowires（Ag NWs）and two-dimensional MXene are used as flexible conductive materials to develop a resistive flexible strain sensor based on MXene and silver nanowires（Ag NWs）,which can monitor the physical state（physiological signal and movement）of aircraft personnel and the aircraft structure in real time.The specific research content and results are as follows:（1）Silver nanowires（Ag NWs）were prepared by hydrothermal method,thermoplastic polyurethane（TPU）prepared by electrospinning technology was used as the flexible substrate,and Ag NWs/TPU flexible strain sensor was prepared by spraying on the surface of TPU fiber film.The Ag NWs/TPU flexible strain sensor was characterized,and the influence of the amount of Ag NWs on the strain sensing performance of the sensor and its application in human motion monitoring were explored.The results show that only a few Ag nanowires are formed at 160℃for 8h,and most of them are still Ag Cl particles.When the reaction time is 16h,the diameter and number of silver nanowires increase,and the formation rate is further improved.When the reaction time is 24h,Ag Cl particles are almost completely transformed into Ag nanowires with an average diameter of about 200 nm and a length of 10-15μm.When the reaction time reached32h,the length of silver nanowires did not increase,but the diameter further increased,and the generation efficiency of silver nanowires decreased.The Ag NWs/TPU flexible strain sensor sprayed with 4m L silver nanowire conductive material with a mass concentration of 2mg/m L has the best sensitivity and strain range.It has a strain sensing range of 0-60%and a high sensitivity of GF=100.During 200 tension-release cycles,the relative resistance waveform of the sensor is basically the same.And can realize the human movement（knee bend,gills,finger bend,elbow bend）accurate sensing.（2）In order to further improve the strain sensing range and sensitivity of the sensor and realize the versatility of the sensor,two-dimensional conductive material Ti₃C₂T_x was obtained by in-situ hydrofluoric acid etching of Ti₃C₂T_x MAX,and thermoplastic polyurethane（TPU）fiber film was used as the flexible substrate.MXene/Ag NWs/TPU flexible strain sensor was prepared by loading MXene/Ag NWs conductive material on the fiber film by spraying method.The MXene/Ag NWs/TPU flexible strain sensor was characterized,the influence of the mass ratio of MXene and Ag NWs on the sensor sensing performance was explored,and the electric heating performance and photothermal performance of the sensor were tested.The results show that the Ti₃C₂T_x and Ti₃C₂T_x particles appear obvious stratification after 12h etching,and the Ti₃C₂T_x products are not obvious stratification due to the short etching time.After 24 h etching,Ti₃C₂T_x is stratified obviously,the shape of Ti₃C₂T_x nanosheet is complete,and there is no missing edge of the layer.After 36 h etching,the edge of the nanosheet becomes missing and the edge comminution is serious.The single-layer Ti₃C₂T_x nanosheet is about 100-300nm in diameter.The MXene/Ag NWs/TPU flexible sensor with the addition of MXene conductive material has a great improvement in sensitivity and sensing range compared with the Ag NWs/TPU flexible sensor with only Ag NWs.The MXene/Ag NWs/TPU flexible sensor has a wide strain sensing range of 0-120%and a high sensitivity of GF=33100.The response time of the sensor is very short,only 157ms,and the resistance changes very stably at different tension frequencies.The MXene/Ag NWs/TPU flexible sensor is very stable with no change in resistance waveform after 1000 stretch-release cycles.The sensor is also capable of accurately sensing physiological signals（pulse）and movements（gills,finger flexing,wrist flexing,elbow flexing and knee flexing）.MXene/Ag NWs/TPU flexible sensor can be heated rapidly under low pressure drive,with good electric heating capacity（at 6.5V low pressure,can reach 64.7℃）and photothermal capacity（light intensity of 500 m W/cm2 under the sun 69.1℃）.（3）Using one-dimensional silver nanowires and two-dimensional MXene as conductive materials,MXene/Ag NWs composite film was obtained by using the mixed dispersion liquid of MXene and Ag NWs in the form of vacuum filtration.The composite film was encapsulated by polydimethylsiloxane（PDMS）,and MXene/Ag NWs composite film flexible sensor was obtained.The MXene/Ag NWs composite thin film flexible sensor was characterized,the influence of the mass ratio of MXene and Ag NWs on the sensor sensing performance was explored,and the electric heating performance of the sensor and the real-time monitoring function of the aircraft structure were tested.The results show that the sensitivity of MXene/Ag NWs composite thin film flexible sensor is the highest when the mass ratio of MXene to Ag NWs is 2:1,and the high sensitivity of 2793 is achieved in the small strain range of 0-1%.The sensor passes 1000 loading and unloading cycles,and there is no difference in the relative resistance curve of the sensor in all cycles.The sensor was pasted on the aircraft structure（aluminum alloy）to monitor its stress to achieve the health monitoring of the aircraft structure.15,000 high-cycle fatigue experiments were conducted on the aluminum alloy specimen（frequency:5Hz）,and the relative resistance curve of the sensor was always very stable.The MXene/Ag NWs composite thin-film flexible sensor also has excellent electric heating performance（up to 73℃at low pressure of 3.5V）,which ensures that it can still complete real-time monitoring of aircraft structure in low temperature environment.