Charge Storage And Piezoelectricity Of The New Polar And Nonpolar Ferro-electric Polymer Film Electrets

With the rapid research developing of dielectric materials, the concept of ferroelectric polymers is not only limited in polar ferroelectric polymers with intrinsic dipoles and domains, but the nonpolar polymers after which was charged under suitable parameters also have the functional properties of piezoelectricity, ferroelectricity and pyroelectrcitiy. Such the new kind of nonpolar polymers which were defined as "ferroelectrets" extended the range of ferroelectric polymers. In this thesis, cellular PP films were studied as the representative nonpolar ferroelectric polymers. The thesis deals with the influence of pressure expansion method on the electret properties of cellular PP, on the dielectric character during the charging of PP ferroelectrets and on the charge dynamics and charge stability of cellular samples. By means of several investigation methods, the piezoelectricity and charge dynamics of the new copolymer of P(VDF-HFP) were studied in comprehensive extent. Besides, the difference and similarity between the above two kinds of ferroelectric polymers (nonpolar ferroelectric polymers and polar ferroelectric polymers) were also discussed in detail based on research results of other groups and ours.The pressure expansion has great effect on the improvement of piezoelectricity of cellular PP. The thesis explored the influence of such process on trap characters, on charge stability and charge dynamics of cellular PP. The experimental results discovered the two-faced effect of the process on the decrease of charge stability and obvious increase of charge storage ability. With the corona charging in combination with the reverse-polarity corona charging compensation method, the polarization of cellular PP ferroelectrets was estimated; the dielectric character variety of sample and the electret properties of two roles of space charges (macroscopy dipoles and their compensation) were also discussed. The research results explained the increased conductivity and the decreased charge stability should attribute to the formation and enhancement of macroscopy dipoles. Also, the density variety of macroscopy dipoles does effect on the transportation character of detrapped charges. For cellular electret...