Doctor of Philosophy
Australian Institute for Innovative Materials
Zheng, Tian, Development and Characterization of Polymer-based Magnetoelectric Nanofibers, Doctor of Philosophy thesis, Australian Institute for Innovative Materials, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/150
With the rapid development of bionics, where biological systems meet electronics, there is an interest in polymer-based electrode systems that are soft, flexible, easily processed and fabricated. In this research area, magnetoelectric (ME) composites bring new and exciting opportunities, including contactless or “wireless” electrical stimulation, less-invasive integration in the form of dispersible, injectable nanoelectrodes, and applications as biodegradable sensors and bioenergy harvesters in the biomedical field. When ME composites are exposed to a magnetic field, a magnetostrictive (MS) component transfers strain to a piezoelectric (PE) component that generates an output voltage. In doing so, ME composites have the ability to enable magnetic-to-electrical conversion and thus can be utilized to power devices or electrically stimulate tissues or cells from a remote magnetic stimulus. To date, ceramic materials have mostly been applied in nanostructured ME composites, however, these may become fragile and cause deleterious reactions at the interface regions, leading to low electrical resistivity and high dielectric losses and ultimately low output voltage.
To overcome these shortcomings, polymer-based ME composites offer new solutions to develop softer, contactless electrodes, without electrical connections, for easier and unique fabrication approaches (e.g. incorporation into soft gels). Their strain-mediated ME effect in large scale devices has been thoroughly studied both experimentally and theoretically. Polymer-based ME composites have almost exclusively used the PE polymer, poly (vinylidene fluoride) (PVDF), due to its high PE coefficient and as such developments in exploring other types of PE polymers have not been forthcoming. For example, other PE polymers such as poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) and poly (lactic acid) (PLA) have yet to be investigated though have the potential to bring added-value and function to polymer-based ME composites. Compared to PVDF and its copolymer P(VDF-TrFE), the piezoelectricity of another copolymer, P(VDF-HFP), is less-well understood. As a biocompatible polymer, PLA has been extensively investigated for applications in drug delivery and tissue engineering. Instead of being used only as a biodegradable and bioactive thermoplastic material, PLA is promising as a PE polymer, which has potential to mimic PE functions of tissues. Thus, in addition to PVDF, the thesis investigates the PE properties of P(VDF-HFP) and PLA and aims to develop ME composite nanofibers based on these polymers.