Piezo-,pyro- and ferroelectricity of odd-numbered polyamides: poling in a soft state, structure-property relations, and electro-active properties
Final Report Abstract
A special chamber for poling at a soft-state was designed and fabricated. The poling chamber provides well-controllable conditions for an electric field application on a polymer film at a high temperature (corresponds to the so-called “soft state” for polymer films). Due to the complicated fabrication work of the chamber, the experimental results on soft-state poling are pending for collection and publishing. In addition, because of the intrinsic proton conductivity found in odder-numbered polyamides, a reliable conductivity-blocking layer film is in searching and testing for the polyamides. As a substitute, i.e. before the fabrication work of the chamber finished, experimental work on another ferroelectric polymer PVDF and its copolymers was performed as that had described in the project proposal. At the soft state, polymer films exhibit more free volume for molecular chains movement, especially for the chains rotation. Our primary results show that at the soft state, PVDF films achieve crystalline phase transition from nonpolar to polar easier with the presence of a proper defined electric field. A field up to 45 MV/m is possible to be applied on an nonpolar (alpha phase) PVDF film at a high temperature of 156 °C. An oriented gamma phase film is achieved after the electric field application for 2 min. The film shows clear piezoelectric activity (piezoelectric d33 coefficient of around 8 pC/N) after a further electric poling with field of 120 MV/m at 135 °C. A better controllable poling condition is expected to obtain with our soft-state poling chamber. It indicates an effective way of piezoelectric polymer film fabrication on a substrate (independent with stretching). The detailed study on P(VDF-HFP) films shows that a much enhanced polarization introduced by melt-quenching plus stretching. With the method, polarization gets around 50% enhanced comparing with only cast and stretched film. This is the result from the much increased beta phase content and the increased crystallinity. Stretching on melt-quenched films produces only growth of beta phase crystallites, however, the stretching on cast films has to contribute to both the crack of alpha phase and the growth of beta phase crystallites.
Publications
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“Enhanced piezoelectric activity in melt-quenched and stretched poly(vinylidene fluoride-hexafluoropropylene) films”, 13th International Symposium on Electrets (ISE 13), Sep. 2008, pp. C107 - C107
Feipeng Wang, Peter Frübing, Werner Wirges, and Reimund Gerhard
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“Solvent-cast poly(vinylidene fluoride) films under electric field”, 9th European Conference on Application of Polar Dielectrics (ECAPD 9), 2008
Feipeng Wang, Peter Frübing, and Reimund Gerhard
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“Effect of stretching on crystalline structure and morphology of poly(vinylidenefluoride-hexafluoropropylene) films”, Joint meeting of 12th international meeting on ferroelectricity (IMF-12) & 18th IEEE international symposium on the applications of ferroelectrics (ISAF-18), Sep. 2009
Feipeng Wang, Peter Frübing, Werner Wirges, and Reimund Gerhard
