Master thesis: "Electrospun Polymer Nanofibers for Electromechanical transduction investigated by Scanning Probe Microscopy"

The ferroelectric copolymer P(VDF-TrFE), has attracted, in recent years, a great interest in scientific research for modern electronics applications, such as energy harvesting for self-powered wearable devices, biomedical sensors and nonvolatile memories. Lots of efforts have been spent in the development of fabrication procedures that could enhance the electromechanical performance of this material. Electrospinning has been proposed as an efficient and low-cost solution for the production of polarized polymeric nanofibers, ready for the integration in devices without post-poling process required. In this thesis, I employ Scanning Probe Microscopy techniques to provide an accurate investigation of the electromechanical properties of single P(VDF-TrFE) electrospun nanofibers. I find that electrospinning does not induce ferroelectric polarization of the fibers, but leads to the accumulation of space charges in the material. I argument that such a space charge gives rise to an apparent ferroelectric response at the macroscopical scale due to the electret effect. Further, after dissipation of the space-charges, with the implementation of high voltage Switching Spectroscopy-PFM, I could demonstrate that poling processes at the level of a single nano-fiber are possible and that the observed piezoelectric performance is comparable to the thin-film behavior. Therefore, I predict that elestrospun fibers will show improved behavior in electromechanical devices once complete poling of fiber networks is achieved.