Vibration energy harvesters, or energy scavengers, recover mechanical energy from their surrounding environment and convert it into useable electricity as sustainable self-sufficient power sources to drive micro-to milli-Watt scale power electronics in small, autonomous, wireless devices and sensors. Using semiconducting, organic piezoelectric nanomaterials are attractive in low-cost, high resistance to fatigue, and environmentally friendly applications. Significantly, the deposition processes of sputtering ZnO (zinc oxide) thin films with high c-axis preferred orientation and electrospun PVDF (polyvinylidene fluoride) nanofibers with high piezoelectric £]-phase crystallisation are controlled at room temperature. Thus they don¡¦t have the necessity of post-annealed and electrical repoling process to obtain an excellent piezoelectricity, and are suitable for all flexible substrates such as PET (polyethylene terephthalate) and PI (polyimide). These works are divided into two parts. Part 1: Flexible piezoelectric harvesters based on ZnO thin films for self-powering and broad bandwidth applications. A new design of Al (aluminum)/PET-based flexible energy harvester was proposed. It consists of flexible Al/PET conductive substrate, piezoelectric ZnO thin film, selectively deposited UV (ultraviolet)-curable resin lump structures and Cu (copper) foil electrode. The design and simulation of a piezoelectric cantilever plate was described by using commercial software ANSYS FEA (finite element analysis) to determine the optimum thickness of PET substrate, internal stress distribution, operation frequency and electric potential. With the optimum thickness predicted by developed accurate analytical formula analysis, the one-way mechanical strain that is efficient to enhance the induced electric potential can be controlled within the piezoelectric ZnO layer. In addition, the relationship among the model solution of piezoelectric cantilever plate equation, vibration induced electric potential and electric power was realized. ZnO thin film of high (002) c-axis preferred orientation with an excellent piezoelectricity was deposited on the Al/PET by RF (radio-frequency) magnetron sputtering in room temperature. Al was sputtered on the PET substrate as the bottom electrode because of its low sheet resistance, superior adhesion with PET, and lattice constants matching with ZnO thin film. The selectively deposited UV-curable resin lump structures as proof mass were directly constructed on flexible piezoelectric plate using electrospinning with a stereolithography technique. One individual harvester achieves a maximum OCV (open-circuit voltage) up to 4V with power density of 1.247 £gW/cm2. This self-powered storage system can drive the warning signal of the LED (light emitting diode) module in both resonant and non-resonant conditions. We also succeeded in accomplishing a broad bandwidth harvesting system with operating frequency range within 100 Hz to 400 Hz to enhance powering efficiency. This system comprises four units of individual ZnO piezoelectric harvester in the form of a cantilever structure connected in parallel, and rectifying circuit with storage module. In addition, a modified design of a flexible piezoelectric energy-harvesting system with a serial bimorph of ZnO piezoelectric thin film was presented to enhance significantly higher power generation. This high-output system was examined at 15 Hz. The maximum DC (direct current) voltage output voltage with loading was 3.18 V, and the maximum DC power remained at 2.89 £gW/cm2. Furthermore, in order to examine the deformation between interfaces and the adhesion mechanism of multi-layer flexible electronics composites (e.g., ITO (indium tin oxide)/PET, Al/PET, ZnO/ITO/PET, and ZnO/Al/PET), nanoscratching and nano-indention testing (nanoindenter XP system) were conducted to analyze the adhesion before and after the vibration test. The plastic deformation between the ductile Al film and PET substrate is observed using SEM (scanning electron microscopy). Delamination between the ZnO and Al/PET substrate was not observed. This indicates that Al film provides excellent adhesion between the ZnO thin film and PET substrate. Part 2: Pre-strained piezoelectric PVDF nanofiber array fabricated by near-field electrospining on cylindrical process for flexible energy conversion. In various methodologies of energy harvesting from ambient sources, one-dimensional nanoharvesters have been gaining more attention recently. However, these nanofibers fabricated by micro-forming technologies may not easily control their structural diameter and length. This study originally presented the HCNFES (hollow cylindrical near-field electrospining) process to fabricate permanent piezoelectricity of PVDF piezoelectric nanofibers. Under high in-situ electric poling and strong mechanical stretching effect during HCNFES process, large PVDF nanofiber array with high piezoelectric £]-phase crystallisation was demonstrated. These pre-strained piezoelectric PVDF nanofibers fabricated by HCNFES with high process flexibility at low cost, availability in ultra-long lengths, various thicknesses and shapes can be applied at power scavenge, sensing and actuation. Firstly, PVDF nanofibers lay on a PET substrate, silver paste was applied at both ends of fibers to fix their two ends tightly on a Cu foil electrode pair. The entire structure was packaged inside a thin flexible polymer to maintain its physical stability. Repeatedly stretching and releasing the nanoharvester (NH 1) with a strain of 0.05% at 5 Hz vibration created a maximum peak voltage and current of -50 mV and -10 nA in forward connection, respectively. Secondly, a total of 44 parallel nanofibers have been fabricated and transferred onto an IDT (interdigital) electrode with 64 electrode pairs as a nanohavester (NH 2) to amplify current outputs under repeated mechanical vibration and impact tests. Under a repeated maximum strain of 0.14% at 6 Hz vibration, a peak current of 39 nA and peak voltage of 20.2 mV have been measured. Impact testing at 15 Hz, peak current of 130 nA has been collected with a voltage of 24.4 mV. Finally, the single PVDF fiber as nanoharvester (NH 3) with a strain of 0.05-0.1% at 5 Hz vibration created a maximum peak voltage and current of -45 mV and -3.9 nA, respectively. The maximum power remained at 18.45 pW/cm2 with a load resistor of 6.8 M£[. Based on the mechanism of converes piezoelectric effect, ANSYS software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. From the observation of actuation property, a fixed-fixed single nanofiber was tested under different DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized.

<p>Funkcionalni materijali na osnovu elektrospinovanih nanovlakana nalaze sve veću primenu u raznim oblastima industrije: biomedicina, farmacija, senzori, filrtacija, ambalaža itd. Elektrospining tehnika je jedna od metoda za dobijanje materijala na osnovu nanovlakana iz polimernih rastvora kori&scaron;ćenjem visokog napona. Kori&scaron;ćenje elekrospining tehnike ima brojne prednosti u odnosu na konvencionalne tehnike, pre svega zbog lakoće inkorporacije aktivne komponente u polimernu matricu, a i specifične morfologije i 3D strukture, jer usled nanometarskih dimenzija, vlakna imaju veliki odnos specifične povr&scaron;ine i zapremine i poroznosti, samim tim veliku kontaktnu povr&scaron;inu sa supstratima, reaktivnim agensima i mikroorganizmima. Zbog proizvodnje materijala na nanonivou, aktivna komponenta se fino dispergije u polimernoj matrici i time se obezbeđuje bolja aktivnost ovih materijala. Za razliku od konvencionalnih filmova, funkcionalni materijali na osnovu elektrospinovanih nanovlakana su aktivni po celoj zapremini. Cilj ove doktorske disertacije bio je optimizicija procesnih parametara elektrospininga i validacija aktivnosti funkcionalnih materijala za različite primene, &scaron;to je postignuto pravilnim odabirom materijala i aktivnih komponenti, optimizacijom sastava materijala, karakterizacijom materijala adekvatnim metodama i validacijom aktivnosti materijala. Razvijeni su materijali za primenu u oblasti kozmetike, ambalaže, filtracije, senzora, stomatologije i provodnih materijala, čija je aktivnost verifikovana u laboratorijskim uslovima (TRL 4).</p> / <p>Functional materials based on electrospun nanofibers are increasingly used in various fields of industry: biomedicine, pharmacy, sensors, filtration, packaging, etc. Electrospining technique is one of the methods for obtaining nanofibers from polymer solutions using high voltage. The use of electrospinning technique has many advantages over conventional techniques, primarily because of the ease of incorporation of the active component into the polymer matrix, as well as the specific morphology and 3D structure, because due to the nanometer dimensions, the fibers have a large ratio of specific surface area to volume and porosity, and thus a high contact surface with substrates, reactive agents, and microorganisms. Due to the production of materials at the nanoscale, the active component is finely dispersed within the polymer matrix, thereby ensuring better activity of these materials. Unlike conventional films, functional materials based on electrospinned nanofibers are active throughout the volume. The aim of this PhD thesis was to optimize the electrospining process parameters and validate the activity of functional materials for various applications, which was achieved by proper selection of materials and active components, optimization of material composition, characterization of materials by appropriate methods and validation of material activity. Materials have been developed for use in the fields of cosmetics, packaging, filtration, sensors, dentistry and conductive materials, the activity of which has been verified under laboratory conditions (TRL 4).</p>