Study On Preparation And Piezoelectric Properties Of Composite Fiber Membrane Prepared With Modified BT And PVDF

Polyvinylidene fluoride（PVDF）has certain piezoelectric properties,easy processing,good flexibility,good stability and other characteristics,showing great potential in flexible wearable,however,PVDF’s piezoelectric coefficient is relatively low,limiting its application range.Barium titanate（BT）particles are widely used to enhance the piezoelectric properties of composites because of their high piezoelectric coefficient,lead-free and low cost.The piezoelectric material composed of piezoelectric BT particles and piezoelectric polymer not only shows relatively high piezoelectric property,but also shows strong flexibility.However,the poor dispersion of BT particles in the PVDF matrix limits the improvement of piezoelectric properties of the composites.Moreover,the dielectric constants of BT particles and PVDF are very different,and its high piezoelectric properties must be realized in the high polarization electric field.In order to solve the problem of poor dispersity of BT particles in PVDF matrix,this paper prepared core-shell polydopamine/barium titanate（pBT）particles by using polydopamine（PDA）as surface modifier for BT particles,which improved the agglomeration problem for BT particles in PVDF matrix.On this basis,in order to solve the problem of inadequate polarization of BT particles,silver nanoparticles were grown in situ on the surface of pBT particles using the reducibility of PDA,and strawberry silver nanoparticles modified pBT particles were prepared（Ag@pBT）.The introduction of silver nanoparticles could enhance the local electric field around the pBT particles during the polarization process,making them fully polarized.Furthermore,the piezoelectric properties of the composites were improved.The main research contents and results of this paper are as follows:Part Ⅰ:Modification of polydopamine on the surface of BT particles and properties of pBT/PVDF composite piezoelectric fiber membraneIn order to improve the dispersibility of BT particles in PVDF matrix,the core-shell structure of pBT particles was prepared by surface modification of BT particles using PDA.The effects of dopamine concentration and modification time on the morphology,structure and hydrophilicity of pBT particles were studied,and the preparation conditions were optimized.pBT/PVDF composite piezoelectric fiber membrane was prepared by electrospinning.The effects of spinning process parameters on the piezoelectric properties of pBT/PVDF composite piezoelectric fiber membrane were studied.On this basis,using pBT/PVDF composite piezoelectric fiber membrane as piezoelectric functional material,the pBT/PVDF piezoelectric nanogenerator was prepared and its piezoelectric performance was measured.The results showed that the optimized conditions for preparation of pBT granules were as follows:dopamine concentration 3g/L,reaction time 16h at room temperature,and the modified pBT particles were uniformly dispersed in the composite piezoelectric fiber membrane.When the pBT particle content was 3wt%,theβphase content of pBT/PVDF composite piezoelectric fiber membrane was 87%,and d₃₃ was 20pc/N.The piezoelectric performance of the pBT/PVDF composite piezoelectric fiber membrane was significantly improved than that of the unmodified.The output voltage of the prepared pBT/PVDF piezoelectric nanogenerator can reach 1.24V,which was 0.37V higher than that of the unmodified.The results showed that using PDA as the surface modifier for BT particles can effectively improve the dispersion for BT particles in PVDF matrix and enhance the piezoelectric properties of the composite piezoelectric fiber membrane.Part Ⅱ:Preparation of strawberry Ag@pBT particles and properties of Ag@pBT/PVDF composite piezoelectric fiber membraneIn order to give full play to the piezoelectric properties of pBT particles and improve the piezoelectric properties of composite piezoelectric fiber membrane,the experiment used silver ammonia solution as silver source and polydopamine on the surface of pBT particles as reducing agent to prepare strawberry shaped silver nanoparticles modified polydopamine/barium titanate（pBT）particles（Ag@pBT）.The effects of the concentration of silver ammonia solution and reaction time on the morphology and structure of Ag@pBT particles were studied,and the preparation conditions were optimized.The effect of Ag@pBT particle content on the piezoelectric properties of Ag@pBT/PVDF composite piezoelectric fiber membrane was investigated by electrospinning.On this basis,Ag@pBT/PVDF piezoelectric nanogenerator was prepared with Ag@pBT/PVDF composite piezoelectric fiber membrane as piezoelectric functional material,and its piezoelectric properties were measured.The results showed that the optimum conditions for the preparation of Ag@pBT particles were as follows:the concentration of silver ammonia solution was0.04mol/L and the reaction temperature and time was 60℃for 3h.TEM showed that the surface of Ag@pBT particles was uniformly loaded with Ag nanoparticles.When the Ag@pBT particle content was 1.5wt%,the piezoelectric constant(d₃₃)of Ag@pBT/PVDF composite piezoelectric fiber membrane was 27pc/N,which was7pc/N higher than that of pBT/PVDF composite piezoelectric fiber membrane.The output voltage of Ag@pBT/PVDF piezoelectric nanogenerator can reach 1.87V.It was1.5 times that of the pBT/PVDF piezoelectric nanogenerator,Ag@pBT/PVDF piezoelectric nanogenerator output voltage remained stable after 800 cycles of testing,showing good piezoelectric stability.The introduction of Ag nanoparticles promoted the polarization of pBT particles under the action of spinning electric field,and further enhanced the piezoelectric properties of Ag@pBT/PVDF composite piezoelectric fiber membrane.The results of this study showed that the use of PDA to modify the surface of BT particles can better solve the problem of poor dispersion of BT particles in PVDF matrix,and effectively improve the piezoelectric properties of pBT/PVDF composite piezoelectric fiber membrane.The introduction of silver nanoparticles on the surface of pBT particles effectively improved the polarization degree of pBT particles in the spinning process,and further improved the piezoelectric properties of the composite piezoelectric fiber membrane.The Ag@pBT/PVDF piezoelectric nanogenerator had excellent output piezoelectric performance and its stability,and can be applied to the real-time monitoring of human movement.It is expected to be applied in wearable electronic devices,implantable biomedical devices,smart textiles and other fields in the future.