Research On Polyvinylidene Fluoride Printing Based On Electrohydrodynamic Jet Printing

Polyvinylidene fluoride(PVDF)is currently a widely used polymer material in the piezoelectric field due to its excellent piezoelectric properties,good mechanical properties,and non-toxic and harmless safety.At the same time,because the device made of PVDF has flexibility that other inorganic piezoelectric materials cannot achieve,it is widely used in the construction of wearable sensors.The current design and manufacture of flexible sensors are facing many challenges such as high precision,cost and time-consuming and the emergence and development of controllable,adjustable,and micro-nano precision EHD printing technology provides the design and manufacture of flexible sensors.Therefore,the study of PVDF printing technology based on EHD jet printing technology and its application in fully printed flexible sensors has important theoretical significance and application prospects.Based on the electrohydrodynamic jet printing technology,this paper uses PVDF mixed dimethylformamide(NMP)ink as the printing material to study the printing process and performance.To achieve highprecision printing in the electro-jet printing process and ensure that the printed samples have excellent piezoelectric properties,the jet formation process and the droplet ejection process of the electro-jet printing are simulated in stages from the perspective of numerical simulation,and then used Experimental exploration is complementary to verify the simulation results.The concrete contents as following:1.PVDF printing based on EHD jet printing can be divided into four processes: cone jet formation,jet breaking to micro-droplets,droplets moving in the printing control,and droplets spreading on the substrate.Due to the boundaries conditions of the four processes are different,and the multi-physics simulation software COMSOL is used to simulate the PVDF printing process in stages.2.The jet formation process of electro-jet printing is mainly manifested in the formation of Taylor-cone and droplets.Based on the theory of EHD dynamics,the relationship between different needle plate spacing,needle type and voltage parameters and cone jet morphology is studied first through the cone jet model.Then,the droplet diameters formed by jet breaking under different voltages are measured by the droplet model.The research results show that the two-stage method can better simulate the formation process of EHD jet printing through the different boundary conditions of Taylor cone and droplet formation.The process parameters of the jet formation stage of PVDF printing are that the needle model is 22G?28G,the power supply voltage is set to 2?6 k V and the distance between the needle and the substrate is set to 2 mm.3.The ejection process of droplets is specifically manifested as movement,deformation and deposition under multi-field coupling,which can be simulated by the electric field distribution and droplet diameter determined by the jet formation model.First,the dynamic model based on the droplet is used to analyze the movement process of the droplet in the air and calculate its final velocity in the jet.Then the spatial electric field distribution is set as the boundary condition analysis the deformation process of the droplet in the electric field.Finally,the boundary conditions of the substrate are set to study the relationship between the electrojet printing speed and the deposition process of the droplet.The research results show that the increase in voltage reduces the printing accuracy.4.Based on the homemade EHD jet printing experimental device,the influence on printing accuracy is studied by experiments.A series of PVDF films is prepared by using different processing parameters,and their structure is quantitatively studied by optical microscope and scanning electron microscope combined with digital image processing technology.The experimental results show that within the selected process parameters,the change of voltage has little effect on the printing accuracy,and the substrate temperature has a greater impact on the compactness of the film.Using the stable load provided by the fatigue tensile machine(MTS)and the self-built charge amplifier circuit,the piezoelectric constant of the printed sample is calculated by the positive piezoelectric effect equation of PVDF.The possibility of preparing a smart sensor is explored finally.