Development And Application Of MXene Based Flexible Force Sensitive Materials

In recent years,portable,foldable,and wearable flexible devices have attracted the attention of world wild researchers,and have gradually become an important frontier research field.Compared with traditional electronic devices,flexible electronic devices have greater flexibility and meet customers’requirements for equipment deformation.They have huge application development potential in medical monitoring and treatment,sports fitness,communications and entertainment,and aerospace.Among them,the flexible strain sensor is one of the typical representative of flexible electronic devices,which can convert the strain change of the device into an electrical signal for output.When the sensor is knitted or assembled on clothing or skin,it can obtain uninterrupted information about human activities anytime,anywhere.Therefore,flexible strain sensors have a wide range of applications in robots,handheld consumer electronics,displays,and medical monitoring equipment.Sensitivity and strain sensing range are the two most critical performance parameters of flexible strain sensors.In general,in order to meet the monitoring of the full range motions of the human body,the sensor needs to reach the goal that the sensitivity is greater than 100 in the entire strain range and the strain sensing range is greater than 50%.However,achieving high sensitivity requires significant structural changes in the device under very small strains,while a wide strain sensing range requires that the device still maintain the connectivity of the conductive structure under large strains,which are often contradictory to each other and difficult to achieve the both.In order to prepare a flexible strain sensor with a large strain sensing range and high sensitivity at the same time,there are usually two major preparation strategies.One is to adopt a special structural design to introduce special features such as grids,spiral structures and bionic structures into the sensor device structure to improve the comprehensive performance of the sensor.However,the complexity of the sensor structure places higher requirements on the manufacturing process,and it is difficult to achieve large-area preparation,which limits their practical application.Another strategy is to choose a new type of sensitive material and use the material’s own microstructure to make the flexible electronic sensor achieve good stretchability and bendability without damaging its electronic performance.This requires the material itself to have good electrical conductivity and flexibility.At present,the commonly used flexible electronic sensor sensitive materials are mainly metal materials and carbon materials.However,sensitive materials with a single morphology often cannot meet the requirements of both highe sensitivity and wide sensing range.It can be seen that the material microstructure design and morphology control of sensitive materials are critical factors affecting sensor performance,and discovering a suitable material with controllable morphology and structure is the key.MXene,which is a two-dimensional transition metal carbide or carbonitride,is a new type of graphene-like layered two-dimensional crystalline material.MXene has many excellent properties such as good electrical conductivity and hydrophilicity,strong mechanical properties,and a mature and controllable preparation process,being widely used in the fields of energy storage,catalysis and electromagnetic shielding.Although MXene is usually defined as a two-dimensional material,by adjusting the experimental conditions during the preparation of MXene,it can presents other morphologies besides two-dimensional sheets,such as irregular particles,nanofibers,etc.,providing more possibilities for the material microstructure design.The flexible strain sensors based on MXene materials exhibit superior performance such as high sensitivity,large strain sensing range,and good cycling stability without complicated structural design and manufacturing processes,and show great development prospects in the field of flexible electronics.As the earliest successfully synthesized MXene material,Ti₃C₂T_x has the characteristics of mature preparation technology and stable properties.This project will use Ti₃C₂T_x as the research object to carry out the following studies:（1）Controllable synthesis of Ti₃C₂T_xThis project systematically studied the differences in the morphology,surface groups,stability,conductivity,and flexibility of Ti₃C₂T_x samples prepared from three typical etchants HF,TMAOH,and Li F/HCl,and the reasons for the differences.We also systematically summarized the advantages and disadvantages of Ti₃C₂T_x samples etched with different etchants,effectively promoting the customization of Ti₃C₂T_x for specific fields according to different requirements.（2）A High-performance flexible strain sensor based on Ti₃C₂T_x nanoparticle-nanosheet hybrid networkThis project used chemical liquid phase etching to prepare Ti₃C₂T_x materials.By changing the type of etchant,etching time and ultrasonic time in the preparation process,and regulating the proportion of nanosheets and irregular particles,a unique Ti₃C₂T_xnanoparticles-nanosheet hybrid network structure was constructed.The flexible strain sensor based on this structure works in accordance with the segmented sensing mechanism.The good synergy between particles and nanosheets and the suppressed crack propagation effect of the network enabled the sensor to obtain a sensitivity of178.4-1176.7,a strain sensing range of 53%,a low detection limit of 0.025%and a good cycling stability,enabling real-time monitoring of human body movements.（3）A flexible strain sensor based on Ti₃C₂T_x/multilayer graphene layered structureIn order to further improve the sensing performance of the flexible strain sensor,we added multilayer graphene into Ti₃C₂T_x with the leading morphology of irregular particles to construct a Ti₃C₂T_x/graphene/PDMS layered structure,and adjusted the content of graphene to make sure the synergistic effect between Ti₃C₂T_xand graphene is maximized.The brittle upper layer in this structure was mainly composed of densely packed Ti₃C₂T_x particles,which improved the sensitivity by generating cracks,while the flexible graphene/PDMS layer in the bottom was used to protect the conductive pathways and increase the sensing range.The sensor based on this layered structure exhibited excellent sensing performance,including an extremely high sensitivity（190.8-1148.2）,a wide sensing range（74.1%）,a low detection limit（0.025%）,and a good cycle stability（more than 10,000 times）.In addition,the structure of the sensor was very simple and the fabrication procedure was cost effective,which endowed the sensor with great application potential.（4）A flexible strain sensor based on Ti₃C₂T_x sheet/silver nanoparticle（Ag NPs）multi-dimensional composite structureWhen Ti₃C₂T_x sheets are used as the sensitive material for flexible strain sensors,effective slippage can not be realized due to the close stacking and interaction of the sheets.In this project,a 0D-2D multi-dimensional composite networkwas constructed by doping Ag NPs between Ti₃C₂T_x sheets.Ag NPs had the function of increasing the interlayer distance,weakening the interaction force between the sheets and working as lubricants,effectively improving the comprehensive performance of the sensor.The sensor based on this structure had an extremely high sensitivity（greater than 123.56）,a wide sensing range（57.47%）,a low detection limit（0.025%）and a good cycle stability（more than 5000 times）.