Polyvinylidene Fluoride Matrix Composite And Its 3D Printing Piezoelectric Sensor Preparation

In recent years,the combination of emerging 3D printing technology and functional materials,in an economic and efficient way to manufacture designable devices began to receive attention.Polyvinylidene fluoride(PVDF)has been used in many fields such as sensors,actuators and energy harvesters because of its excellent electrical activity and good flexibility.It is an ideal material for3 D printing to manufacture designable devices.As a kind of 3D printing technology,FDM pringting has the advantages of low cost,small footprint and simple operation,which is a good choice for preparing 3D printing devices.PVDF has a variety of crystal forms.Among them,the polar phase,especially the ? phase,whose F atom is completely located on the side of the polymer chain,makes PVDF show excellent piezoelectric and dielectric properties.By increasing the polar crystal content of PVDF matrix,the dielectric and piezoelectric properties of PVDF can be enhanced,thus promoting its further application in sensing and energy utilization.In this study,the synergistic effect between ionic liquids(IL)and multi-walled carbon nanotubes(MWCNT)was used to promote the formation of ?-PVDF.On this basis,the composite material and FDM printing are combined to produce the piezoelectric sensor,and the one-printing of the piezoelectric sensor is realized.This preparation method provides a new direction for the design and manufacture of sensor,which is conducive to the development of designable,high degree of freedom PVDF-based 3D printing functional devices.Firstly,PVDF was modified by MWCNT to prepare PVDF/MWCNT composites.The results showed that MWCNT improved the electrical and thermal conductivity of PVDF,but the dispersion of unmodified carbon nanotubes in the matrix was not good,and it had little effect on the increase of ? crystal content and dielectric properties.The addition of IL promoted the dispersion of MWCNT in PVDF matrix,but had little effect on the thermal conductivity and melt flow of the composites.At the same time,the synergistic effect of the two can promote the formation of polar ? crystals,and the content of effective ? crystals increases by up to 141%.Moreover,PVDF/IL/MWCNT composites have high dielectric constant and low dielectric loss.The dielectric constant at 100 Hz reaches 26.55,which is 355% higher than that of pure PVDF,and the dielectric loss is below 0.38 within the test frequency range,which meets the practical application requirements.Secondly,the properties of FDM printing products of PVDF composites with different IL/MWCNT ratios were compared.Taking PVDF/1.5%IL/1% MWCNT composites as the research object,the effects of FDM printing conditions on bending properties,porosity and crystallization properties were explored.The nozzle temperature will affect the melt flow.The higher the nozzle temperature is,the better the adhesion of the wire is,and it is beneficial for the PVDF molecular chain to break the energy barrier and transform into ?-PVDF,but excessive temperature is a waste of energy.The platform temperature affects the cooling crystallization process of the melt,and the temperature should not exceed the crystallization temperature of the composites.Printing speed has a great influence on the crystallinity of the composites,reducing the printing speed appropriately is beneficial to improve the quality of the products,but it will reduce the crystallinity and the printing efficiency is low.Excessive printing speed will affect the mechanical properties of products.The best FDM printing parameters of composite material are as follows: nozzle temperature is 240 ?,platform temperature is 140 ?,printing speed is 30 mm/s.Finally,based on the FDM printing parameters of PVDF/IL/MWCNT composites with high ?-phase content and combined with the model design,the one-printing of the piezoelectric sensor is realized.The sensor can respond well to pressure,and the output voltage signal is almost proportional to the input pressure.In the test range,the maximum output voltage can reach 5.8 V,and the pressure sensitivity can reach 2.65 V/k Pa.Without post-polarization processing,the sensor is much more sensitive than many reported 3D printing PVDF piezoelectric devices,and has good durability and stability,which can be used for the measurement of small pressure stimuli in life and real-time monitoring of human motion.