Preparation And Performance Of Electrospun PVDF Nanofiber Membrane Based Flexible Piezoelectric Devices

With the vigorous development of informatization and emerging electronic industries,flexible wearable devices have become an important position for scientific research and industrial transformation around the world.Flexible wearable piezoelectric sensors are flexible devices that can convert mechanical stimuli into detectable electrical signals.They have excellent flexibility and mechanical properties,and have important application prospects in the fields of soft robots,wearable devices,and human-machine interfaces.The development background of flexible and wearable piezoelectric sensors is mainly due to the rapid development of electronic technology and material science.In recent years,with the increasing demands for human health,sports activities,and quality of life,the requirements for sensors are also increasing.Traditional rigid sensors often have shortcomings such as large size,heavy weight,and uncomfortable wearing,which cannot meet people’s needs.Therefore,flexible and wearable piezoelectric sensors emerged as a new candidate.With the continuous development of flexible electronics technology,nanomaterial technology,biomedical engineering technology and other fields,flexible and wearable piezoelectric sensors have made great progress.This thesis reports an investigation on the development of a ZnO@Ag/PVDF piezoelectric nanofiber membrane based flexible piezoelectric sensor device.Firstly,the ZnO@Ag/PVDF piezoelectric nanofiber membranes were fabricated by electrospinning technology.The composite fiber membrane was modified by the synthesized ZnO@Ag functional filler;and the piezoelectric properties of the membranes were evaluated.The results show that the ZnO@Ag/PVDF film has high piezoelectric coefficient and flexibility,which are essential for the preparation of flexible piezoelectric devices.Secondly,the nanofibrous membrane was fabricated into a flexible piezoelectric sensor,and its performance was tested.The results show that the flexible piezoelectric sensor has good sensitivity and stability and can be used to measure pressure in different ranges.Finally,in order to simulate the tactile perception of the skin,a flexible piezoelectric array sensor signal acquisition system was constructed,and remarkable progress has been made in increasing the sensitivity and detection range of the sensor.The main work and results of this thesis are summarized as follows:1.The ZnO@Ag functional filler was synthesized by a chemical process,and the PVDF piezoelectric fiber membrane was prepared by electrospinning technology.The key influencing parameters in the electrospinning process were explored by the response surface method,and the electrospinning voltage,functional filler concentration,and solution feed rate(flow rate)were optimized for the suitable fibre diameter and membrane properties.2.The optimal doping content of ZnO@Ag functional filler in the preparation of ZnO@Ag/PVDF composite fiber membrane was investigated,and it was found that when the ZnO@Ag content was 7 wt%,the Voc and Isc of ZnO@Ag/PVDF piezoelectric fiber membrane increased to 15.0 V and 1.775 μA compared with pure PVDF fiber membrane(4.3 V,0.329 μA)and ZnO/PVDF fiber membrane(11.1 V,0.634 μA).Although the output value is increased due to the increase of the content,too many doped particles affect the mechanical properties and flexibility of the fiber film.When the ZnO@Ag content is 5 wt%,and the Ag:Zn atomic ratio in the ZnO@Ag is 1:20,the output performance of the fiber membrane is the best,and its Voc is8.03 V,1.775 μA.3.The ZnO@Ag-5wt%/PVDF composite fiber membrane is integrated into a multifunctional flexible sensor.The performance of the device was tested by force/electricity,and the results showed that the pressure sensitivity of the device was 1.817 V/kPa,2.422 V/kPa and 0.367 V/kPa in the pressure ranges of 2.4-6.4 N,6.4-12.8 N and 12.8-17.6 N,respectively.The sensor device can run continuously for more than 5,000 working cycles with stable performance,strong periodicity,and good macroscopic piezoelectric properties.4.Based on the ZnO@Ag/PVDF piezoelectric fiber membrane,a wearable flexible piezoelectric array sensing signal acquisition system was designed and manufactured.Considering that the flexible design of the array is more conducive to the collection of multicontact and large-area information,flexible electrodes were fabricated through the "mask + jet printing" process.The flexible array is composed of 4×4 piezoelectric units.In the research of the circuit,the signal acquisition module,the gating module and other module circuits were reasonably designed to realize the pressure display function of the sensor,which can perform long-term dynamic monitoring of the external pressure of the human body.The system is expected to be applied in practical fields such as remote medical monitoring and robotic electronic skin.