Electro-Mechanical Properties of Electron Irradiated P(VDF-TrFE) Copolymers Under Different Mechanical Stresses
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For electro-mechanical applications, a material exhibiting a high electric field induced strain response is always highly desirable. Recently, a very high electric field induced strain response was observed in many EAP systems [2], such as heavily plasticized poly(vineylidene fluoridetrifluorethylene [P(VDF-TrFE)] [3], polyurethane and silicone [3], [4]. Very recently, we reported that high energy electron irradiated P(VDF-TrFE) copolymer film exhibits a very large electric field induced strain response [5], [6]. The irradiated P(VF-TrFE) copolymers possesses a very high elastic energy density besides the high strain response since the material is of relative high elastic modulus compared to other EAP [5], [6]. In addition, these polymers have many advantages over ceramics/crystals, such as low cost, flexible, easy to process and shape. All these make the electroactive polymer (EAP) very attractive for a broad range of electromechanical applications [2]. In most electromechanical applications, the material is under some mechanical load condition. Thus, for a soft polymeric material, the electromechanical properties of the material under different stresses conditions or the load capability of the material is always an important concern. In this paper, the studies of the electric field induced strain response of irradiated P(VDF-TrFE) copolymer under different mechanical boundary conditions are reported. The results show that the material has high load capability.
71 Mat. Res. Soc. Symp. Proc. Vol. 600 0 2000 Materials Research Society
EXPERIMENT P(VDF-TrFE) copolymer powders were purchased from Solvay and Cie, Bruxelles, Belgium. The compositions used here are 50/50, 65/35, and 68/32 mol%. The copolymer films studied here were prepared using two approaches: melt press and solution cast. In the melt press process, the copolymer powders were pressed between two pieces of aluminum foil at 215 to 240 *C. In the solution cast method, the copolymer powders were dissolved in dimethyl formanide (DMF) and then the solution was cast on a flat glass plate and dried in an oven at 70 'C. Two types of films, the stretched and unstretched films, were studied in this work. For the unstretched films, the films prepared above were annealed at 140 °C for a time period between 12 to 14 hrs to improve the crystallinity. In order to prepare the stretched films, the films made from solution cast or quenched from melt press were uniaxially stretched up to 5 times at a temperature between 25 to 50 'C. The stretched films were then annealed at 140 °C for 12 to 14 hrs to increase the crystallinity. During the annealing process, the two ends of the stretched films were mechanically fixed. The crystallinity of the final films is about 75%. The thickness of the films was in the range from 15 to 30 aim. The electron irradiation was carried out in nitrogen atmosphere at different temperatures with an electron energy of 2.55 MeV, 1.2 MeV, and 1.0 Mev. In order to characterize the electric filed induced strain response, gold electrodes of a thick
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