.pvdf / Batio <sub> 3 </ Sub> Composite Films And Features

Polyvinylidene fluoride (PVDF) is a piezoelectric polymer with low density, low acoustic impedance, excellent chemical stability and high mechanical strength. It can be easily processed to large area or irregular shape. Piezoelectric ceramics have excellent dielectric, piezoelectric properties and large mechatronics coupling coefficient. Therefore, the composite of PVDF and piezoelectric ceramic not only possesses the advantages of ceramic and polymer such as high piezoelectricity, high flexibility, low density and easy processing, but also overcomes the disadvantages of each pure component. In this work, the preparation and characterization of PVDF and piezoelectric ceramic composite have been carried out, especially PVDF/BaTiO3 piezoelectric film and PVDF-BaTiO3/PDDA multilayer ultrathin film have been focused on.Firstly, PVDF/BaTiO3 composite film with various thickness and different mass ratio was produced by solution casting method, and the optimum parameters using 2% g/cm3 PVDF solution at 80°C solidifying temperature for 3 h with the assistance of 5 h ultrasonic dispersion were obtained. The thickness of produced thin films is between 20 and 50μm. From AFM analysis, it has also been found that the film with the mass ratio of BaTiO3 to PVDF between 0.1 and 0.2 has higher flexibility, more uniform grain dispersion, more compact surface morphology, and is easier to be produced into large area flexible composite film. Electrical analysis showed that the film with 20~100μm thickness and 0.6~0.7 mass ratio of BaTiO3 to PVDF has the highest piezoelectricity.Then, multilayer PVDF/PDDA composite ultrathin film was fabricated by alternative electrostatic layer-by-layer (LBL) self-assembly (SA) with negative polarized PVDF film. The results from AFM analysis showed that the surface of ultrathin film with PVDF concentration 1% g/cm3 is smoother, more uniform, and more compact than that with 0.1% g/cm3 PVDF. By in situ monitoring using QCM, it was found the thickness of each layer ultrathin film is almost identical when the layer number is less than 20. Estimated from Sauerbery equation and measured with spectrometric ellipsometer, the average thickness was less than 10 nm, and the composite ultrathin film was mainly polycrystalline from XRD analysis. Electrical characterization showed that composite ultrathin film had ferroelectric and pyroelectric properties, which is worthy studying further.Finally, PVDF-BaTiO3/PDDA multilayer ultrathin film was prepared using electrostatic SA method. It was found via QCM monitoring that, uniform thin film could be processed when the mass ratio of BaTiO3 to PVDF was 1 instead of 0.5. Based on approximate calculation by Sauerbery equation, ultrathin film layer thickness ranged from 19 to 25 nm. The ferroelectric property of PVDF-BaTiO3/PDDA ultrathin film was significantly improved with the presence of BaTiO3 ferroelectric ceramic nano-powder, which was modified by VMS coupling agent.