Study On Crystallization Behavior And Property Manipulation Of PVDF-based Ferroelectric Polymers

Ferroelectrics possess favorable pyroelectric and electrocaloric properties,whose polarization changes with the variation of temperature and electric field and can realize the mutual transformation of electric energy and thermal energy.Compared with inorganic materials,polymers with flexibility and resistance characteristic have great application prospect in the field of wearable electronic devices.However,the polarization of polymer is much less than that of inorganic material so that it could not meet the demand for ferroelectric materials with high sensitivity and efficiency in the infrared detector,energy collector and electrocaloric refrigerator.Stress can affect the crystallization behavior and polarization of polymer,which is an effective way to manipulate the properties of polymer.Thus,the effect of stress on crystallization behavior and ferroelectric properties of PVDF and its copolymer are studied in this paper.First of all,the PVDF film is prepared by spin coating to solve the problem of polarization of PVDF.The shear stress induced by spin-coating can affect the crystallization behavior of PVDF.As a result,theβphase content and the crystallinity of obtained PVDF increase.The polarization of spin-coated film is 28.2μC cm^-2 and the pyroelectric coefficient is 0.92×10^-8 C cm^-2 K^-1.The results indicate that the application of stress can improve the ferroelectric properties of polymers.Based on the study of shear stress,nano-confined stress is applied to P（VDF-TrFE-CFE）to prepare ferroelectric polymer nanowire arrays by template method.The result shows that nano-confined stress increase the crystallinity to 51.7%and decrease crystal size and induced crystal orientation.Thus the electric polarization is strengthened to 5.4μC cm^-2.At last,it is found that the stress induced unique crystallization behavior greatly improved the electrocaloric properties of polymer:the temperature change is 0.7 ^oC and the entropy change is 6.0 kJ m^-3 K^-1。Meanwhile the nanochannels of the polymer nanowires array-AAO hybrid film accelerate heat flow.The result proves that stress can adjust the properties of polymer again and pushes the progress of efficient,environmental friendly solid state refrigeration technology.