Preparation And Senstive Behavior Of Fibrous Conductive Composite With Porous Structure

Conductive polymer composites(CPCs)are prepared based on conductive filler and polymer matrix,which not only has good conductivity,but also has the characteristics of flexible and easy-to-process.In recent years,it attracts increasingly attention because its potential applications such as self control heating material,electromagnetic shielding,thermometer and gas sensors,etc.Flexible wearable strain sensor,as one of the most important application direction for CPCs,which has broad application prospects in human-computer interaction,health monitoring and human motion monitoring.In this paper,in order to obtain fiber-shaped wearable strain sensors which combine a wide detection range and high sensitivity,and further eliminate the"shoulder peak"phenomenon and weaken the hysteresis effect in the response process.We prepare carbon nanotubes(CNTs)/thermoplastic polyurethane(TPU)and reduced graphene oxide(RGO)/CNTs/TPU flexible conductive polymer composite fibers via uniaxial wet-spun and coaxial wet-spun-dipping,respectively.We study their strain-sensitive response behaviors,and the specific research contents and conclusions are as follows:1?Preparation and performance study of CNTs/TPU strain sensor(1)First,we obtain a suspension by blending CNTs and TPU.Subsequently,CNTs/TPU suspension is extruded via uniaxial wet-spun to prepare CNTs/TPU composite fibers.By changing the experimental parameters(the diameter of the extrusion needle),the size and internal structure of CNTs/TPU composite fibers can be controlled.And it further can realize controling its sensing performance.(2)We investigat the effect of the appearance of porous structure and the change of fiber diameter on its sensing performance.With the appearance of porous structure and the increase of fiber diameter(0.26 mm,0.31 mm,1.08 mm,2.07 mm),the detection range of CNTs/TPU composite fiber is increasing(62%,102%,249%,320%),but there is no significant change in GF(4.31,4.10,4.09,3.81)during the same strain range(0-10%).For cycle stability,we define M/N as the retraction ratio of theconductive network in the cyclic response of the composite fibers,where N is the peak value of the first cyclic response,and M is the difference between the peak value of each subsequent cyclic response and the peak value of the first cyclic response.With the increase of diameter,the M/N values are 43.0%,32.5%,29.1%and 14.5%,respectively in the second cycle.The above results indicate that CNTs/TPU composite fibers with the largest diameter and the appearance of porous structure has better sensing performance.Therefore,we choose the conductive polymer composite fiber with the largest diameter and porous structure for the further study.(3)The internal porous structure and the distribution of CNTs are characterized via SEM,showing that CNTs are selectively distributed on the pore walls to form an effective conductive network.(4)In the tensile test,the selected fiber shows a wide detection range(320%)and high sensitivity(GF=97.5 at 320%strain),fast response time(about 125 ms).At different tensile rates the fiber-shaped strain sensor exhibits consistent response behavior.The fiber-shaped strain sensor is also conform to ohmic characteristics at different tensile strains.For durability,the fiber-shaped strain sensor can be used above 9700 cycles,which exhibits excellent cycle stability and reproducibility.(5)We adopt the tunnel theory to analyze the two-stage GF in the response process and further explain the mechanism in the tensile response process.(6)We apply the medical tape to fix the selected fiber-shaped sensor on joint to detect the human body motion in real time,such as finger bending,wrist bending,elbow bending,etc.Moreover,the material is sensitive to detect different motions by distinguishing the various peak shapes of curves,showing a high resolution,which indicates the potential application of this material in wearable flexible strain sensors.2.Preparation and performance study of RGO/CNTs/TPU-TPU strain sensor(1)We prepare the conductive polymer composite fiber through a coaxial wet-spun-dipping method,the composite fiber has a three-layer structure,the core layer is pure TPU as a supportting layer,CNTs/TPU of the skin layer and RGO of the surface layer RGO are sensitive response layers.Through SEM we observe that the composite fiber has a porous structure in the core layer and the skin layer.We can also observe that CNTs form an effective conductive network on the inner pore walls of the skinlayer through TEM.It is clearly showed that the RGO of the surface layer and the CNTs of the skin layer exist connection.The effective synergy between the fillers allows the fiber to obtain a dual conductive network structure.(2)The tensile response behavior of the fiber is studied.The fiber has outstanding tensile properties(686%elongation at break),a relatively wide detection range(120%),and high sensitivity(GF=300 at 120%),fast response time(282 ms)and excellent durability(over 9300 cycles).(3)Based on infrared,ultrasonic in water and immersion in boiling hot water,it is found that RGO,CNTs and TPU have a certain binding force and have good durability.(4)We systematically study the cyclic response behavior of the fiber under different strains.It is found that the"shoulder peak"phenomenon do not occur whether under small strain or large strain,and the resistance of the fiber can nearly recover to initial condition during the releasing process.Meanwhile,force and resistance change synchronously during the cycles.(5)Based on the high sensitivity and excellent response behavior of the fiber,the fiber-shaped strain sensor can be attached on the face or abdomen for real-time monitoring of the aspiration behavior and the breathing behavior.Meawhile,the sensor can be attached on joint to measure response behavior at different movement angle,which provides a good basis for its application in wearable devices.