Fabrication Of Flexible Strain Sensors With Various Patterns By 3D Printing And Its Applications

With the development of smart technology,flexible and stretchable strain sensors have attracted significant interests due to their potential in wearable electronics,monitoring of human motion and healthcare,and so on.Conductive polymer composites can be used as flexible and stretchable strain sensors directly,which are usually composed of conductive materials and flexible substrates.Various methods have been used to synthesize such flexible strain sensors.Among them,3D printing technology has the advantages of batch preparation and easy patterned design,which is used to synthesize strain sensors.In this thesis,the multi-walled carbon nano-tubes(MWCNTs)were used as a conductive material,which has a high ratio and easily entangle.Ecoflex was chosen as the polymer substrate,due to its advantage of good stretchability.Using the 3D printing technology,the flexible strain sensors with line-shape pattern and other different patterns were printed.The effects of synthesis conditions and patterns on the performances of devices were studied,and the applications were investigated in integration of devices and detection of human motion too.The main research contents and conclusions are as follows:1.Using the 3D printing technology,the line-shape MWCNTs/Ecoflex flexible strain sensors were prepared by the MWCNTs / IPA solution with concentration of 1wt% and 2 wt%.Among them,the sensor prepared by 2 wt% MWCNTs / IPA solution has a higher sensitivity.The obtained samples have good repeatability and excellent durability.In addition,the effects of curing time of Ecoflex prepolymer on the sensitivity of strain sensor were studied.The results show the sensitivity of sensor increases with Ecoflex curing time firstly,and then decreases.When the curing time of Ecoflex is 12 min,the line-shape MWCNTs/Ecoflex strain sensor has the highest gauge factor(GF),about 23.9,in the range of 0-100% tensile strain.The prepared sample can accurately detect the slight movement of human facial muscles,respiration and pulse.In addition,the prepared sensors were design into a 4×4 array,which can achieve monitoring of spatial distribution of the applied pressure.2.Utilizing the 3D printing technology,the flexible MWCNTs/Ecoflex strain sensors with different patterns,including zigzag-shape,ring-shape,Θ-shape and double ring-shape patterns were printed,and the effect of patterned structure on performance of device is investigated.Compared with the line-shape strain sensor,the sensitivity of the zigzag-shape strain sensor is lower,but the resistance can reach the equilibrium of response quickly after stretching.The Θ-shape strain sensor has the highest GF,about 121.6 and 405.3 in the range of 0-140% and 140-180% tensile strain,respectively.Furthermore,the response of ring-shape strain sensor is isotropic to strain.The Θ-shape strain sensor can identify the tensile strains of longitudinal and transverse.The double ring-shape strain sensor can identify the tensile strains of longitudinal,45°oblique and transverse.The results show the patterned design can not only regulate the performance of sensors,but also further expand the function of sensors,which has the important reference value to the design and application of strain sensors.