Fabrication And Properties Of Mxene Based Flexible Pressure/Strain Sensors

With the rapid development of wearable devices,robotics and biomedical electronics,the application of flexible stress/strain sensors for health monitoring,disease diagnosis and motion detection has attracted a lot of attention.MXenes have become a strong contender as active materials for stress/strain sensors due to their excellent electrical conductivity,good hydrophilic properties and mechanical flexibility.Unfortunately,its excessively good conductivity makes the range of resistance change under stress/strain too small,resulting in low sensitivity and narrow operating range,which seriously hinders its development in practical applications.Therefore,it is of great importance to develop stress/strain sensors with a simple preparation process,good sensing performance,comfort and portability.In this paper,the MXene-based flexible stress/strain sensor is constructed by optimising the composite material preparation,structural design and electrode material selection,and the research is carried out in terms of fabrication process,performance testing and device application respectively.The main work is as follows:(1)Flexible pressure sensor based on oxidized Ti₃C₂T_X MXene film was developed.The Ti₃C₂T_X-Ti O₂ composite film was prepared by spontaneous oxidation of MXene and assembled into a"sandwich"structured flexible pressure sensor.A series of physical characterisation methods were used to analyse the morphology and composition of the films and to investigate their sensing properties.The device can be used as an electronic skin to monitor human physiological activity in a personalised manner.The good sensing properties highlight the promising potential of pressure sensors based on MXene oxide for more integrated flexible electronic devices.(2)Layered tactile sensor based on MXene@ZIF-67 film was developed.The MXene@ZIF-67 composite film with a layered structure was prepared by alternate filtration of MXene solution and ZIF-67 dispersion.The alternating layers of MXene and MOFs form a three-dimensional interconnected conductive network,increasing the range of variation in the conductive pathway.The flexible sensing device exhibits excellent sensing performance with a sensitivity of up to 110.0 k Pa^-1 and a wide pressure detection range of 0.0035-100 k Pa.The fabricated sensor is able to monitor various stimuli over a broad pressure range,such as recognition of finger movements;it is also able to detect weak signals such as pulse and vibrations caused by the sound of a musical instrument,which successfully realises the device's versatility.(3)A pressure sensor based on MXene/ZIF-67/PAN composite fiber film with a rough structure was developed.By in situ growth of ZIF-67 particles on PAN fibers,a flexible nanofiber film with a rough structure was obtained.A three-dimensional conductive network structure was further constructed by introducing MXene nanosheets.The assembled device exhibited high sensitivity(62.8 k Pa^-1),a wide operating range(0-100 k Pa),fast response/recovery time(10 ms/8 ms)and strong mechanical stability(over 10 000 cycles).Simulations of the human urinary system have also been carried out,confirming that it can provide effective bladder volume monitoring and demonstrating the promising applications of this flexible pressure sensor in the medical field.(4)The controlled assembly of MXene nanosheets as electrodes and active layers for high-performance electronic skins was investigated.MXene was used instead of conventional electrodes as the electrode material for the flexible sensor,and the contact between the electrode and the active layer was made tighter by vacuum filtration.The sensing performance of the flexible device fabricated with MXene electrodes is significantly better than that of the device with other conventional electrodes.In addition,the MXene/PAN-based flexible pressure sensor exhibits strong mechanical stability and can withstand 240 bending cycles.Finally,inspired by origami technology,the device is enlarged or folded like a jigsaw puzzle or origami,transforming from a two-dimensional(2D)to a three-dimensional(3D)structure and increasing the versatility and portability of flexible electronic devices.(5)MXene based fiber strain sensors for human-computer interaction were explored.The 3D interconnected Ti₃C₂Tx@P(VDF-Tr FE)fiber film was prepared by simple,process-controlled electrospinning technique and then wrapped on a pre-stretched elastic yarn substrate.Due to the good electrical conductivity of MXene and the unique wavy 3D network structure of the film,the resistance of the composite film changes significantly in response to external forces,thus providing excellent strain sensing performance.The prepared sensor exhibits a high gauge factor(GF)of 108.8over a strain range of 45-66%and excellent durability of over 1600 stretch/release cycles.Finally,a data glove was designed to correspond different gestures and expressions to form an intelligent gesture-expression control system,further confirming the great potential of this strain sensor for human-computer interaction and wearable electronics.