Preparation And Properties Study For Flexible Resistive Mechanical Sensor Based On CNTs

With the development of flexible electronics and e-skin research,flexible mechanical sensors aiming at sensing various types of stress are receiving more and more attention,because of its application prospect in the field of flexible human-computer interaction,robotics,biomechanics and other fields.Carbon nanotubes(CNTs)have a wide range of applications for the filled nanoconductive particles in composites and flexible electrode,and provides many possibilities for preparing flexible mechanical sensors,because of its good electrical conductivity and high aspect ratio.In this paper,the aim of research was to study the performance of the flexible strain sensor for sensing the surface tension and the flexible pressure sensor for sensing the surface pressures,the optimum preparation technology of carbon nanotube dispersion was discussed,and the feasibility and preparation of flexible sensor were analyzed.Then the flexible strain sensor based on carbon nanotubes and the flexible piezoresistive sensor based on the new microstructure were designed and fabricated,and the performance of the two kinds of sensors was studied.Firstly,the possible factors influencing the performance of multi-walled carbon nanotubes(MWCNTs)dispersions were analyzed.Experiments set up four groups of variables in the comparative dispersion experiment.Through the characterization of data and practical application,it is found that the use of solvent for the dispersion of deionized water is more convenient and safe,and the addition of surfactant to non-covalent bond can effectively improve the concentration and stability of the dispersion.In the range of 50W-150 W,the concentration of the dispersion increases with the increase of the ultrasonic power.In the range of 10-20 min,the concentration of the dispersion is proportional to the ultrasonic time.Based on these conclusion,it was determined that 20 mg of MWCNTs were dispersed with 60 ml of deionized water and an appropriate amount of surfactant,and the MWCNTs dispersion was prepared at an ultrasonic power of 150 W and an ultrasonic time of 20 min.On the basis of the MWCNTs dispersion,the flexible strain sensor of carbon nanotubes was prepared by spraying process,and the performance test was carried out by mechanical-electrical test platform.It is found that the electrical and mechanical properties of the sensor are closely related to the preparation process.When the number of spraying times is more than 30 times,the sensor has conductivity and strain response,but the effective strain range is very low.Once the strain exceeds this range,the sensor will become invalid;And with numerous spraying time,the conductivity of sensor is more excellent,the effective strain range is relatively high.Based on the difference of effective strain range,the sensitivity and linearity of the number of less spraying(less than 55 times)and multiple spraying(more than 55 times)were tested respectively.The results showed that: the sensitivity of the sensor with less spraying time is relatively high(6.846),and the linearity is low.With the increase in the number of spray,the sensitivity decreased from 6.846 to 2.158,while the linearity increased from 0.851 to 0.984.This sensor is suitable for applications in micro-strain recognition scenarios.The sensitivity of the multi-sprayed sensor is low and the linearity is high(0.996).With the increase of the number of spraying,the sensitivity continues to decrease to 1.282,linearity is always maintained at a high level.This sensor is suitable for the field of large strain linear monitoring.Aiming at the high sensitivity in sensing surface pressure,a flexible piezoresistive sensor based on MWCNTs pyramid array/patterned electrode structure was designed,and the pressure response mechanism of the sensor was described and the sensor was prepared.The results of the sensor performance test shows that the device has a outstanding pressure response capability,the response time is 0.2s,and the sensor can maintain stable electrical response under repeated loads,has good reliability;In the low pressure range(less than 100Pa),the sensor has a ultra-high sensitivity(-9.95kPa-1),about 100 times higher than that of an unstructured sensor.Furthermore,the influence of the pyramid structure and the patterned electrode on the sensitivity of the sensor was discussed by preparing the sensor based on MWCNTs pyramid array / flat electrode and the sensor based on flat MWCNT conductive layer / flat electrode based flexible sensor.The pressure response curve shows that the sensitivity of the sensor based on the MWCNTs pyramid array / flat electrode is-5.13kPa-1 in the low pressure range(less than 100Pa),and the sensitivity of the sensor based on flat MWCNT conductive layer / flat electrode base flexible sensor is-0.1kPa-1.By discussing the conduction mechanism of the three structural sensors,it is revealed that the sensitivity of the pyramid structure and the patterned electrode is improved by 50 times and nearly 2 times respectively.