Investigationof Structure And Performance In Stress Sensing Behaviors Of Conductive Polymer Composites

Conductive polymer composites(CPCs)based on polymer matrix and conductive fillers have been extensively investigated due to their popular applications in many fields,such as sensors,electromagnetic interference shielding,and self-regulating heaters,etc.CPCs have excellent behaviors of strain,temperature,gas and liquid sensing.Because of the outstanding behavior of strain sensing in CPCs,their applications have been paid close extensive attention in the motion detection device,wearable and strain sensors and flexible electronic skin.CPCs strain sensors have many excellent performances in easy processing,low cost,etc.However,many problems need to solve(such as CPCs hysteresis effect in strain sensing and bad repeatability,etc.),limiting their applications.In order to control the CPCs’ performance,it is important to fabricate a new polymer structure.In the field of flexible strain sensor,the mechanical and response performances are critical importance.Research shows that strain sensor based on crack structure possesses high response performance,but its range of response is very limited;strain sensor based on wrinkle has excellent stability,but its responsivity is low.We fabricated a strain sensor based on GNPs/TPU/PDMS crack-wrinkle structure.This new crack-wrinkle structure was realized by exposing the material to a sequential tension and pressure.Wrinkles,composed of GNPs,result uniformly distributed in the TPU layer;uniform cracks are developed on wrinkles with the same orientation.The piezoresistive performance of the sensor was investigated under tension.Our sensor exhibited a high and stable GF(~150)under large strain(0~20%).In morphology analysis,we observed the crack deformation of the strain sensor when subjected to tensile.We discussed the crack opening and closing the influence of the strain sensor conductivity by crack extension and return mechanism.Besides,our CWS sensor could detect quite tiny strain variations(<0.1%)with a fast response(< 90ms).Moreover,the strain sensor demonstrated a high durability(> 20000 cycles).Finally,thanks to its special structure,our strain sensor did not show any hysteresis phenomenon.In addition,the sensor could detect a large set of human movements such as large movements and subtle motions in real-time(such as Joint bending,pulse,vocal cord vibration).Our strain sensor is suitable for applications health monitoring during fitness,electronic skin and other human motion detection.On the other hand,in our study,CNTs,HDPE and UHMWPE were blended by using ethanol assisted ultrasonic dispersion–hot compression method.CNTs were then selectively distributed on the interface between HDPE and UHMWPE matrices through this process.Consequently,the formation of segregated structure within CNTs-filled CPCs can lower the percolation threshold(0.3wt.%)significantly.The microstructure and morphology of the conductive composites were observed by optical microscope.Thus,segregated CNTs/HDPE/UHMWPE CPCs were obtained.This method which has comprehensively considered the morphological control of the polymer and the CNTs particles distribution design has significantly reduced the percolation threshold of CPCs.Then,we study the destruction and rebuilding of conductive network have an effect on behavior of CNTs/HDPE/UHMWPE CPCs strain sensing.Conductive filler increasing improved the electrical and mechanical properties of the CPCs.Furthermore,in the cycle tensile testing,with the increase of cycle number,material residual strain increases gradually.Because of CNTs one-dimensional characteristics and influence of viscoelastic behavior in CPCs,some of CNTs in the process of stretching along the drawing direction orientated again.Then,a more perfect conductive network was formed in CPCs.responsivity peak of the CPCs reduced gradually.Based on the research of the electrical performance,we summed up relationship among conductive filler content,tensile rate and relative resistance.