Fabrication And Performance Of Flexible Piezoresistive Sensors Based On Twodimensional Material MXene

Flexible sensors are an important part of intelligent wearable electronic devices and the Internet of Things（Io T）.In particular,flexible piezoresistive sensors have become one of the research hotspots in the sensor field due to their advantages of fast response time,low cost and high durability.However,at present,flexible sensors in the wide range of pressure detection,high sensitivity,good stability and simple preparation,and other aspects of mutual constraints,all kinds of excellent performance is difficult to obtain at the same time.The performance of the flexible piezoresistive sensor can be improved by optimizing the structure of the sensing element and selecting the appropriate conductive induction material.To this end,this paper selected two-dimensional material MXene（Ti₃C₂T_x）as a new conductive induction material,with the sand cloth shape of polydimethylsiloxane（PDMS）film and clean sponge as the substrate,through the alkaline treatment of Ti₃C₂T_x and the composite with MWCNT,Two kinds of flexible piezoresistive sensors,3D pleated Alk-Ti₃C₂/PDMS and MWCNT/Ti₃C₂T_x sponge,were fabricated by layer assembly technique（LBL）.The effects of the roughness of PDMS substrate,the alkalization degree of Ti₃C₂T_x and the weight ratio of MWCNT/MXene on the performance of the corresponding sensors were studied.The two kinds of sensors developed are applied to monitor human movements（wrist pulse,fingertip joint bending,vocal cord vibration）and the weight of water.The main work and research results are as follows:（1）Layer-by-layer assembly（LBL）technology was used to wrap 3D pleated Alk-Ti₃C₂ alkalized by Na OH as conductive induction material on the microstructure PDMS film with sand-granular surface prepared with rough abrasive cloth as template,and the uneven conductive film of Alk-Ti₃C₂/PDMS was prepared.（2）The influence of abrasive cloth roughness on piezoresistive sensor performance was studied.PDMS films with different roughness were prepared by using 24,36,46,60 and 120 mesh emery cloth as templates.It is found that with the increase of mesh number,the PDMS film becomes rougher,and the rough substrate prepared by 46 mesh emery cloth has the best sensing performance because of its suitable structure.（3）The effect of Na OH alkalization concentration on piezoresistive sensor performance was studied.Alk-Ti₃C₂/PDMS with different folding degrees were obtained by alkaline treatment of Ti₃C₂T_x at concentrations of 0,1,3,5 and 7 M,respectively.It is found that with the increase of concentration（0-5 M）,the folding degree of Alk-Ti₃C₂ becomes more obvious,but when the concentration reaches 7 M,the folding degree decreases.Among them,Alk-Ti₃C₂ treated with 5 M Na OH has the most obvious folding phenomenon,and the addition of-OH and-O functional groups on the surface of Alk-Ti₃C₂ is conducive to the combination of conductive material and flexible substrate,and improves the sensitivity of the sensor.（4）The performance of the piezoresistive sensor（5NMP sensor）prepared by 5 M Na OH alkalized Alk-Ti₃C₂ and 46#PDMS was studied.It is found that the sensitivity of the sensor is increased to 1104.38 kpa-1（1-200 k Pa）while the operating range is extremely wide（>800 k Pa）.In addition,the 5NMP sensor also has a fast corresponding time（100 ms）,a low detection limit（～17 Pa）,and 3000 cycles under a large pressure of300 k Pa,indicating that the sensor has excellent stability.And the sensor has been used to detect pulse,throat vibration and weight monitoring.（5）The conductive MWCNT/Ti₃C₂T_x sponge was prepared by using simple LBL method to compound the MWCNT/Ti₃C₂T_x mixture on the clean sponge.Cleaning sponge with high elasticity and hydrophilicity was used as flexible substrate,and one-dimensional MWCNT and two-dimensional Ti₃C₂T_x were mixed as conductive materials and wrapped on the sponge skeleton to form a unique 3D network structure of conductive sponge.（6）The influence of different weight ratios of MWCNT/Ti3C2Tx mixture（0:1,1:2,1:1,2:1,1:0）on the performance of the flexible piezoresistive sensor was studied.It is found that when the weight ratio of MWCNT/Ti₃C₂T_x is 1:2,it is more conducive to the dispersion of MWCNT/Ti₃C₂T_x which are all electronegative,and more conducive to the combination of conductive materials and flexible substrate.（7）The piezoresistive sensor（1CNT@2MX sensor）prepared by MWCNT/Ti₃C₂T_x sponge with a weight ratio of 1:2 was studied.Found:The sensor has a wide operating range（0-35 k Pa）and high sensitivity(0.086 k Pa^-1),fast response time（80 ms）and excellent stability（5000 cycles）.It has also been used to monitor human movement（joint flexion）.In this paper,two kinds of flexible piezoresistive sensors based on MXene are developed by simple LBL method,and the influence of their substrate materials and conductive materials on the performance of piezoresistive sensors is studied respectively,and the sensor is applied to real life.These results broaden the application of Mxene in the field of sensors and have important reference significance for the preparation of high-performance wearable electronic devices.