Piezoelectric ultrafine polymer and ceramic fibers by electrospinning: process development and characterization
Yördem, Sinan Onur (2006) Piezoelectric ultrafine polymer and ceramic fibers by electrospinning: process development and characterization. [Thesis]
Piezoelectric polymer and ceramic films and fiber mats that may be considered for actuator and sensor needs were fabricated. Solution casting and electrospinning were utilized for Poly(vinyldene fluoride) (PVDF) films and fiber mats, respectively, while zinc oxide (ZnO) fiber mats were fabricated by electrospinning process followed by calcination. Morphology, crystalline structure and mechanical properties of the piezoelectric films and fiber mats were examined and characterized for experimentbased process optimization. Traditional solution casting process produces uniform PVDF films yet with nonpolar crystallinity. Stretching of the solution cast films were carried out to increase the polar crystal phase of PVDF. Stretched and un-stretched PVDF films were characterized according to their polar crystallite contents, and stretching was shown to be vital for β-phase formation in favor of piezoelectricity. Electrospinning process produces mats of ultrafine fibers with diameter ranging from a hundred nanometers to a couple of micrometers, by applying an electrical force to polymer solution. The effects of solvent type, solvent mixture together with applied voltage and collector distance were investigated leading to process parameter ranges to produce planar mats composed of uniform fibers only. All of the parameters were found to have vital roles in the fabrication of fiber mats regarding their morphology and applicability without self-folding and fiber uniformity. In addition, crystallinity, morphology, mechanical property and potential piezoelectric effect of solution cast and electrospun films were analyzed and compared. Electrospun fiber mats were found to be advantageous as in-situ β-phase formation was observed. Nano-scale zinc oxide fibers were also produced by electrospinning, but followed by calcination. Processing conditions such as solution content and heat treatment schemes were optimized in order to obtain uniform ZnO nanofibers. Zinc concentration and the substrate that the sample is placed on were found to be significant towards the uniformity and continuity of the ceramic fibers. Heating rate during calcination was also shown to be effective in fiber morphology and geometry. Fibers of ZnO with ~140nm diameter were produced. In addition, micron-scale ZnO whiskers and rods were also formed during the calcination process.
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