Thermal and Electric Properties of P(VDF-TrFE) and P(VDF-CTFE) Copolymer Blends

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Thermal and Electric Properties of P(VDF-TrFE) and P(VDF-CTFE) Copolymer Blends Zhimin Li, Yuhong Wang, and Z.-Y Cheng Materials Research and Education Center, Auburn University, Auburn, AL36849, USA ABSTRACT PVDF-based electroactive polymers (EAP) exhibit high electromechanical performance that is attractive for developing high performance actuators and sensors. In an effort to develop very inexpensive electroactive polymers, P(VDF-TrFE)/P(VDF-CTFE) copolymer blends are studied and reported. The structure, morphology, thermal transition and miscibility of the blend system were investigated by DSC and X-ray diffraction. It is found that the phase transition behavior of the blends can be significantly modified using thermal and mechanical treatmentss. The modified film exhibits high polarization response and low remanent polarization. More importantly, a high electrostrictive strain of 5% was observed in the treated blends. Combined with Young’s modulus, the results show that the copolymer blends have a electromechanical coupling factor and energy density comparable or even higher than the irradiated P(VDF-TrFE) copolymers. INTRODUCTION Recently, a much higher electromechanical performance was found in high-energy electron irradiated p(vinylidene fluoride - trifluoroethylene) [P(VDF-TrFE)] copolymer [1], and later on in both P(VDF-TrFE-CFE) (CFE – chlorofluoroethylene) and P(VDF-TrFE-CTFE) (CTFE – chlorotrifluoroethylene) terpolymers [2,3]. In order to explore new high-performance and inexpensive electroactive polymers, polymer blends, such as P(VDF-TrFE) with PMMA [4], P(VDF-TrFE) with P(VDF-HFP) [5], P(VDFTrFE) with P(VAc) (polyvinyl acetate)) [6], and PVDF with Nylon-11 [7-8], have been studied. However, the electromechanical performance obtained in polymer blends so far is relatively poor. In this paper, a new blend system, P(VDF-TrFE) and P(VDF-CTFE) copolymer, both of which are semi-crystalline is introduced. The experimental results show that this new blend system is competitive with irradiated EAPs and terpolymers. EXPERIMENTAL DETAILS P(VDF-TrFE) 65/35 mol% (VT65) and P(VDF-TrFE) 75/25 mol% (VT75) copolymers were used as one component in the blends. (VDF/CTFE) 91/9 mol% (VC91) and (VDF/CTFE) 88/12 mol% (VC88) copolymers were selected to be the other component based on research results of the VDF-TrFE-CTFE terpolymer. Blends were prepared by dissolving the VT and VC copolymers in DMF at the following VT/VC wt% compositions: 100/0, 75/25, 50/50, 25/75, 10/90, 0/100. Films were obtained by casting solution on glass substrate and dried at 70 ºC for 8 hrs in oven. The cast film was mechanically uniaxially stretched at room temperature to about 5 times of its original length and annealed at higher temperature (at 120 oC 1 hr first and then 140 o C 1hr). DSC study was conducted using a TA DSC system (model 2910). The sample was heated at a rate of 10 °C/min to above its melting temperature and then cooled down at the same rate. The

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microstructure of the crystalline phase in the blends was char