Study On The Properties Control And Microfluidic Energy Harvesting Device Of PVDF Nanofibers

In recent years,micro-nano sensing systems with low power consumption,high miniaturization and integration degree have become an important part of the Internet of Things system.Traditional sensors driven by additional power supplies have many defects,including complex power supply circuits,large size and difficult power renewal process,etc.Therefore,the research and development of high performance self-powered sensor systems have become one of the hot spots in related fields.Among them,micro-nano energy harvesting devices based on the piezoelectric effect can be used to convert the abundant mechanical energy in the environment into electric energy.Such devices with wide application fields and high output voltage can be used for powering the low-power-consumption sensors.However,related researches on piezoelectric power generation device mostly focus on the energy harvesting performance of devices in atmospheric environment.In opposite,the electromechanical coupling effect of such devices in liquid environment,especially the microfluidic environment still need to be further explored.Moreover,the traditional piezoelectric power generation materials,such as PbTiO₃,（K,Na）NbO₃ and ZnO are limited either by the high toxicity or poor flexibility and low mechanical durability,restricting their practical application in the field of micro-nano scale piezoelectric power generation.Poly（vinylidene fluoride）（PVDF）,as a typical organic piezoelectric materials,exhibits excellent piezoelectric properties,good flexibility and biocompatibility.In this dissertation,the piezoelectric PVDF nanofibers is prepared by electrospinning method.The piezoelectric properties of the nanofibers are optimized through the regulation of the preparation parameters.The applications in the vibration sensing detection and microfluidic mechanical energy harvesting are also systematically studied.The main research results are as follow:（1）The PVDF nanofibers were prepared by electrospinning method.The influence of precursor concentration,electrospinning voltage and other parameters on the structure and piezoelectric properties of PVDF nanofibers were studied.The results show that the size of PVDF nanofibers becomes more uniform with the increase of precursor concentration.The nanofibers obtained with precursor concentration of 0.13 g/mL exhibited the best piezoelectric performance,and the uniformity tends to be worse with further increase of precursor concentration.In addition,when the electrospinning voltage is below 13 k V,the piezoelectric phase content of product increases with the increase of electrospinning voltage and the output voltage of PVDF nanofibers also increases under the same strain condition.This could be attributed to the promotion of PVDF crystal phase shift by high voltage.The further increase of electrospinning voltage leads to the decrease of piezoelectric phase content due to the corona phenomenon.（2）The PVDF-nanofiber-based flexible piezoelectric nanogenerators were fabricated by magnetron sputtering technology.The device generates AC pulse output voltage when it is bended under the external force.In low frequency,the output voltage and current of the device under external force linearly increase with the increase of strain amplitude and frequency.The strain sensitivity reached 0.92 V/rad or 0.61 V/mm with the vibration frequency of 1.54 Hz.When the piezoelectric power generation device is used as a vibration sensor,it could achieve online self-powered sensing for a copper foil piece in damping motion.Using the test method that the copper foil vibration is excited by the vibration exciter in sweeping frequency pattern,the measured resonance frequency of the object is 19.23 Hz.（3）A microfluidic piezoelectric power generation device based on the PVDF piezoelectric nanofibers was designed and assembled.Driven by the microfluid,the PVDF nanofibers in the microfluidic chip generated electrical output to the external circuit.Results indicated that the PVDF nanofibers generated periodic oscillations and pulse voltage output when driven by the gas-liquid phase fluid.When the characteristic diameter of microfluidic chip increases from100?m to 300?m,the output voltages of devices increase to 1.84 V due to the increase of fluid kinetic energy.However,with further increase of characteristic diameter,the output voltage decreased because of the turbulent flow phenomenon.（4）The output voltage of microfluidic chip piezoelectric power generation devices is closely linked with the pressure and viscosity of fluid.When the fluid pressure increased from0.3 bar to 1.0 bar in chip,the output voltage of PVDF nanofibers decreased from 1.89 V to 0.56V due to the strain capacity decrease caused by turbulent flow phenomenon.Furthermore,because of the fluid velocity reduction,the output voltage decreased from 1.13 V to 0.22 V when the fluid viscosity increased from 1.05 mPa·s to 2.94 mPa·s.As a result,this device can be used to test the fluid pressure and viscosity in microfluidic chip without power supply.