Study On Crystallization Behavior And Piezoelectric/ferroelectricity Of Pvdf And Its Copolymer

Amid the few polymers presenting piezo,pyro or ferroelectricity,poly(vinylidene fluoride)(PVDF)and its copolymers have the best all-around electroactive properties,being used as smart materials.PVDF has non-polar phases and polar phases.Polar phases such as ? crystal,y crystal and ? crystal have excellent electroactive properties.Therefore,it is of great significance to fabricate PVDF films with high-content polar phase.In this paper,PVDF single-layer film and PVDF/polyvinylidene fluoride-trifluoroethylene(P(VDF-TrFE))bilayered film were respectively prepared and studied.For PVDF samples,The transition ability of ? to ?' phase was studied and the PVDF films with high-content polar phase were fabricated.we have also studied the preparation of PVDF/(P(VDF-TrFE))bilayered oriented film by epitaxy method to tailor its specific structure to improve its ferroelectricity.The main results obtained are as presented follows:1.Tailor the transition ability of ? to ?' phase abilityIn the present work,?-PVDF spherulites are obtained firstly in the isothermal crystallization process and the transition ability of ? to ?' spherulites is controlled simply through a temperature program.If a cooling process(step 2)follows the isothermal crystallization process(step 1),in the subsequent annealing process(step 3)almost all the? spherulites formed in step 1 transit to ?' spherulites.By contrast,without step 2,rare ?spherulites transit to ?'-phase.By combining in situ characterization methods,both micro-and nano-scale structure evolution is monitored and the mechanism of cooling process taming the transition ability of ? to ?' phase is disclosed.Through specific temperature program,PVDF films with high-content ? phase was obtained,which can also promote the application of PVDF in piezoelectric/ferroelectric devices.2.The structure and ferroelectric properties of oriented PVDF/(P(VDF-TrFE))bilayered filmTo improve the properties of the devices,there is a high requirement on the structure and morphology of the ferroelectric polymer thin film.Although numerous efforts have been made on the controlling the crystal orientation,the work on the tailoring the P(VDF-TrFE)thin film through epitaxy method has been seldom explored.In this work,we spin-coated P(VDF-TrFE)on the oriented PVDF substrate.After thermal annealing,The oriented morphology and molecular orientation of P(VDF-TrFE)are systematically characterized by Atomic Microscopy(AFM),Infrared Spectroscopy(IR)and X-ray Diffraction.Well ordered edge-on lamellar of P(VDF-TrFE)can be observed.It was also found that the c-axis of P(VDF-TrFE)is parallel to the melt-draw direction and b-axis is perpendicular to the substrate.More importantly,the oriented PVDF substrate controls the orientation of the P(VDF-TrFE)film.Furthermore,characterized by piezoelectric force microscope(PFM)and ferroelectric tester,the PVDF/P(VDF-TrFE)double-layer oriented film has good piezoelectric and ferroelectric properties,which provides a basis for the preparation of memory devices with good performance.