Design And Research Of The Sensing Performance Of Graphene Based Flexible Nonwoven Material Strain Sensor

Flexible strain sensors have attracted wide attentions because of their wide application in wearable device fields.The fabric-based sensors have the advantages of good skin-friendliness,air permeability and flexibility.Compared with other sensors based on films,foams and other materials,the fabric-based sensors are close fitting with the human body,so they have been broadly applied during these years.Graphene is an ideal sensing material for flexible strain sensors on account of its stable electrical conductivity and excellent mechanical properties.However,the reported graphene fabric strain sensors still have some defects,such as complicated preparation process,low sensitivity,and inability to simultaneously sense large and small strains.Therefore,in our research,meltblown nonwoven materials with high elasticity and simple preparation process were selected as the substrate,silver nanowires(Ag NWs)with high conductivity and multi-walled carbon nanotubes(MWCNT)with high stability were used to improve the sensor's sensitivity or maximum monitoring strain range,respectively.It is hoped that our researches may provide some new ideas for the preparation of flexible graphene-based fabric strain sensors.Firstly,graphene oxide(GO)was prepared by the modified Hummers method.Then the sodium hydrosulfite(SH)and poly(4-styrene sulfonate)(PSS)were used to reduce GO to reduced graphene oxide(r GO)at high temperatures,respectively.Through characterization,the results showed that GO was successfully prepared,and its surface was rich in oxygen-containing functional groups.After the reduction,the GO was highly reduced to r GO with great conductivity.Then,polybutylene terephthalate meltblown nonwoven material(PBT MB)with good elasticity and flexibility was selected as the substrate,and its surface was decorated with different concentrations of r GO through ultrasonic treatment.SEM characterization and sensing performance tests showed that when the r GO concentration was 3 mg/m L,r GO was uniformly loaded on the surface of PBT MB material.At this moment,the overall performances of this sensor were optimal.Furthermore,both r GO and Ag NWs with differe nt concentration ratios were loaded on the surface of the PBT MB material by ultrasonic treatment.The morphology and structure of r GO/Ag NWs@PBT MB tensile strain sensor were analyzed by SEM,Energy spectrum(EDS)and XRD,respectively.It was found that r GO/Ag NWs were successfully loaded on the PBT MB material.As the loading concentration of Ag NWs increased,the Ag content on the surface of the PBT MB material increased.Sensing performance tests showed that with the increase of Ag NWs concentration,the s ensitivity and maximum monitoring range of the sensor gradually increased.When the concentration ratio of r GO and Ag NWs was 1:0.9,this kind of strain sensor has the best sensing performance.Even if the strain was increased from 80%to90%,it still had a high sensitivity of 1829 and good stability.Thirdly,a thermoplastic polyurethane meltblown nonwoven material(TPU MB)with great tensile strain and good resilience was designed as the other sensor substrate.Thro ugh magnetic stirring,r GO with different concentrations were loaded on the TPU MB.SEM and sensing performance tests showed that when the r GO loading concentration was 2 mg/m L,its sensing performances were better.Then,both r GO and MWCNT with different concentration ratios were loaded on the surface of the TPU MB material by magnetic stirring.The morphology and composition of r GO/MWCNT@TPU MB tensile strain sensor were analyzed by SEM and XRD,respectively.The results indicated that r GO/MWCNT was loaded on the surface of the TPU MB.The sensing performance tests illustrated that with the increase of MWCNT concentration,the maximum detection range of this strain sensor gradually increased,but the sensitivity decreased.When the concentration ratio of r GO and MWCNT was 1:0.5,this strain sensor had the best comprehensive performance and its maximum detection range could be up to 180%.Specially,when the strain increased from 150%to 180%,the sensitivity was as high as 1407.The response time and recovery time were only 0.226 s and 0.246 s respectively.Furthermore,under 100%strain,this sensor still had excellent stability after 1600 cycles of tensile testing.Finally,the r GO/Ag NWs_0.9@PBT MB and r GO/MWCNT_0.5@TPU MB strain sensors were connected to different body positions of the volunteers,respectively,such as leg joints,elbows,wrists,fingers,throat,etc.to monitor large and small body motion signals.O ur researches had revealed that both of these two strain sensors could detect small human body movements,for instance,facial expressions and speech recognition.The detection results in speech recognition of the same words were very similar.However,compared with the r GO/Ag NWs_0.9@PBT MB strain sensor,the r GO/MWCNT_0.5@TPU MB strain sensor had better stability for the detection of large-scale movements,for example,joint movements of the legs.Thus,it was believed that r GO/MWCNT_0.5@TPU MB strain sensor had greater application prospect in the detection of large strain motion.