Research On Preparation And Properties Of PVDF-Based Flexible Pressure Sensors

With the advancement of the 5G era and the applications of Internet of Things technology,various novel technologies have sprung up.Wearable electronic device is one of the important application areas of the Internet of Things,which is of great significance for monitoring human activities/motions and personal healthcare.This thesis mainly focused on piezoelectric flexible pressure sensors.The piezoelectric composite films composed of inorganic piezoelectric material barium titanate?BaTiO₃,BTO?and organic piezoelectric material poly?vinylidene fluoride??PVDF?were utilized to fabricate flexible pressure sensors.Generally,traditional films based on inorganic/organic composite piezoelectric materials face the bottleneck including the poor dispersion and the defects and cracks in the interface between the inorganic piezoelectric material and organic piezoelectric material,which hinders the performance of pressure sensors.Herein,polydopamine?PDA?was introduced as surface modifier to modify BTO nanoparticles,and then was mixed with the PVDF matrix in different proportions to form uniform PDA@BTO/PVDF composite piezoelectric materials.PDA@BTO/PVDF bulk composite films and nanofiber composite films were prepared via solution casting and electrospinning technology,respectively.Afterwards,wearable flexible pressure sensors with"sandwich"structure were prepared.The main work are as follows:1.A series of PDA@BTO/PVDF piezoelectric flexible pressure sensors were prepared by solution casting method.The results show that PDA modification to BTO can reduce the interface defects and cracks between BTO and PVDF,and improve the component dispersibility.Thus,the accumulation trap charges induced by interface defects and cracks reduced greatly,and enhanced the output performance of the pressure sensor.Besides,17wt%pressure sensor demonstrated the optimized performance,with output voltage 9.3V,output current 84 nA,response time 27 ms,sensitivity 64.2 mV/N,and output power 0.122?W/cm2 at 12 N.Furthermore,this pressure sensor was sensitive to various human motions?walking,jumping,running?,showing great potential in the applications of human motion monitoring and wearable electronic devices.2.A series of PDA@BTO/PVDF piezoelectric flexible nanofiber pressure sensors were prepared using electrospinning technology.By investigating the influences of electrospinning process conditions on the nanofiber morphology,the optimal process parameters for preparing nanofibers were obtained.Similarly,the PDA modification to BTO can reduce the interface defects and cracks between BTO and PVDF,which significantly improved the nanofiber surface morphology,and greatly reduced the number of"convex knots"of the nanofibers.Reducing the accumulation of accumulated charge at the interface were beneficial to improve the performance of pressure sensors.Results showed that the 5wt%nanofiber pressure sensors displayed optimal performance under0.07 N,with output voltage 2.2 V,output current 43 nA,and sensitivity 3.95 V/N,which showed extremely high voltage sensitivity.In addition,the sensor has extremely high sensitivity to human radial artery pulse and vocal cord vibration.It can detect the waveform of human radial artery pulses in real time,and distinguish different human voices from vocal cord vibrations to achieve voice recognition.The nanofiber pressure sensors have great potential applications in the fields of medical diagnostics,personal healthcare,biomedicine,and portable wearable devices.