Manufacturing of Poly(vinylidene fluoride) and Evaluation of its Mechanical Properties
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Daniel M. Esterly
Poly(vinylidene fluoride) (PVDF) receives an increasing amount of attention because it exhibits the strongest piezoelectric response of any commercially available polymer. These piezoelectric properties have proved useful as actuators and sensors. Current manufacturing processes limit PVDF to thin films and restricting their uses largely to sensors. Further applications utilizing the changes in mechanical properties of piezoelectric polymers are being realized. Evaluating to what extent the mechanical properties will change with applied electric field and finding new ways to manufacture PVDF will lead to new applications of piezoelectric polymers.
In-situ mechanical testing of biased piezoelectric PVDF films successfully measured changes in loss and storage modulus. In-situ creep testing measured an increase in stiffness while in-situ dynamic mechanical analysis (DMA) measured and overall decrease in loss and storage modulus. Differences in results between the two experiments are attributed to orientation of the polymer and piezoelectric forces acting on the equipment. DMA results are accepted as being the most accurate and measured changes of over 20% in elastic modulus. Results were believed to be greatly influence by attached electrodes and actuation forces.
Cryogenic mechanical milling successfully converted a phase PVDF powder to b phase as measured with wide-angle x-ray diffraction. This is the first recorded instance of b phase powders forming from the a phase through ball milling. These b phase powders maintained their crystal structure during compression molding at 70°C.
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