Preparation Of Polyurethane Based Flexible Strain Sensor And Performance Study

Piezoresistive flexible strain sensors are widely concerned in software robots,intelligent textiles,human health monitoring and wearable electronic devices due to their advantages of portability,flexibility,portability,low cost and flexibility.By introducing conductive nanoparticles build conductive polymer elastomer preparation type pressure resistance strain sensor network is one of the general strategy,however,as a result of conductive particles in the flexible polymer matrix be easy to cause the conductive network distribution,and the lack of interaction between adjacent nanoparticles when applying strain/release cycle,separation of conductive nanoparticles increase in the number,As a result,the resistance of conductive network increases irreversibly,resulting in poor sensing performance and cycling stability.To fabricate flexible strain sensors with both sensitivity and cyclic stability,some innovations must be made in structural design.In view of the above situation,we introduce the electrostatic spinning nanofiber membrane as the substrate of flexible strain sensor,electrostatic spinning film with certain pore,can provide uniform dispersion of conductive particles with the carrier,moreover by ultrasonic immersion method can be further realize the conductive particles uniformly distributed in the electrospinning film,in order to prevent the conductive particles in the matrix loss,etc.,The composite electrospinning film impregnated with conductive particles was hot-pressed in multiple layers to bind the substrate closer to the conductive particles and further disperse the conductive particles uniformly.In this experiment,thermoplastic polyurethane(TPU)nanofiber films with different mass fractions were prepared by electrostatic spinning method.SEM observation showed that when the TPU mass fraction was 10wt%,the surface of the electrospinning film presented bead-like morphology and obvious fiber adhesion.When the TPU mass fraction was 13wt%,the surface morphology of the electrospinning film was good.The fiber diameter distribution is uniform,about 2?m in diameter,and the fiber membrane pores are uniform,which provides a guarantee for the uniform dispersion of conductive particles.When the TPU mass fraction is 17wt%,the fiber diameter distribution range becomes wider,showing obvious polydispersion.Silver nanowires(Ag NWs)with uniform size were prepared by polyol reduction method.Ag NWs and carbon nanotubes(CNTs)were used as conductive particles to construct the sensor network to prepare flexible sensors.By ultrasonic impregnation,Ag NWs and CNTs were compounded on the electrospinning film with a mass fraction of TPU of 13wt%to construct a conductive network using the electrospinning film as the carrier.The intermediate conductive layer of the sensor was prepared by hot pressing after the composite conductive nanofiber membrane was superposed.The upper and lower sides of the conductive layer were hot pressing pure TPU electrospinning film,and wires were connected at both ends to prepare the flexible sensor with "sandwich" structure.The sensor properties of sandwich composite structure during the stretch-recovery cycle were characterized by universal tensile testing machine and digital source table.The effects of Ag NWs and CNTs content on the performance of strain sensor were studied.The morphology of Ag NWs,CNTs and TPU electrospun films were characterized by X-ray diffractometer(XRD)and scanning electron microscope(SEM).The results showed that polyol reduction method successfully prepared Ag NWs with high purity and face-centered cubic structure.The length was about12?m,the diameter was about 60 nm,and the aspect ratio was about 200.TPU electrospinning film has uniform pores,good elasticity and tensile recovery.Ag NWs and CNTs form a conductive network with uniform distribution and good interlap in the pores of electrospinning fiber film.The sandwich structure sensor prepared by multi-layer hot pressing process has excellent sensing performance.When Ag NWs and CNTs are used as conducting particles,the resistance of the flexible strain sensor increases linearly with the deformation in the tensile process,and the linearity is good.When ?=0-15%,the sensitivity(GF)of the sensor prepared with Ag NWs as conductive particles increases with the increase of strain.When ? is 15%,the sensor tends to be stable,GF remains at about 8,and can still maintain good performance after several cycles.When CNTs were used as the conducting particle,the resistance/deformation trend of the sensor was basically the same as that of the silver nanowires.When the strain was 5%,the sensitivity tended to be stable,and GF coefficient was stable at about 6.By comparison,it was found that the sensor prepared by Ag NWs as the conducting particle had higher sensitivity.Comparing the multi-layer hot-pressed "sandwich" structure sensor prepared in this experiment with the traditional PDMS encapsulated "sandwich" structure sensor,it can be found that the performance of the sensor prepared in this experiment has more excellent cycle stability.