In this study, a cylindrical near-field electrospining (CNFES) process will be used to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF) piezoelectric fibers, and a piezoelectric fiber harvesting device with parallel electrode was fabricated to capture ambient energy. First, the PVDF powder was mixed in acetone solution uniformly and the dimethyl sulfoxide (DMSO) was mixed with fluorosurfactant to prepare PVDF macromolecular solution. The PVDF macromolecular solution was filled in a metals needle injector and contacted a high power supply, after the PVDF drops in the needle was subjected to high electric field, the drops became a Taylor cone and overcame surface tension of the solution itself, extremely fine PVDF fiber was formed and jetted out. The fibers were collected numerous and quickly by homemade cylindrical collector and the diameter of fiber could be controlled easily by adjusting the rotating speed of the cylinder and the electric field. From the observation of XRD (X-ray diffraction), it reveals a high diffraction peak at 2£c=20.7¢X of piezoelectric crystal £]-phase structure by adjusting PVDF concentrations and DC voltage. By providing 7Hz shake and 0.23% strain, the piezoelectric fiber harvesting device with parallel electrode could generate 76mV; by providing 7Hz shake and 0.14% strain, the device could generate 1.1nA.

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.

Le transport off-shore du pétrole nécessite l'utilisation de canalisations appelées pipelines. Ces conduites flexibles sont constituées d'une carcasse métallique interne qui assure la tenue mécanique et d'une gaine de pression en PVDF qui garantit l'étanchéité. L'étude est menée afin d'analyser les conditions pouvant conduire à des risques de rupture fragile dans le polymère. Le grade de PVDF choisi est différent du matériau industriel car il ne possède pas de plastifiant. Ce choix a conduit à une extrusion plus difficile et à la formation d'un taux de porosité anormalement élevé (environ 10%). L'étude mécanique du PVDF a été réalisée sur différentes géométries d'éprouvettes afin de montrer l'influence de la sévérité d'un défaut sur le mode d'endommagement et de rupture. Au cours de la déformation, le matériau est caractérisé par un blanchiment marqué, lié à un endommagement par cavitation et à l'étirement de la matière. La rupture ductile du PVDF est favorisée par les températures élevées, les faibles vitesses, les taux de triaxialité faibles et les chargements en flexion. La rupture fragile est en général obtenue pour les températures basses (T

Accurate, non-invasive determination of multiphase fluids distribution in reservoir rock can greatly help the evaluation and monitoring of oil reservoirs. This laboratory thesis research, carried but utilizing the biomedical engineering concepts and measurement facilities, is an important step in developing a novel magnetic field-based oil detection method. When paramagnetic nanoparticles are either adsorbed oil/water interface or dispersed in a fluid phase in reservoir rock pores, and exposed to external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) save. As the first step, the motion of the interface between a suspension of paramagnetic nanoparticles and a non-magnetized fluid (placed in a cylindrical dish) is measured by phase-sensitive optical coherence tomography (PS-OCT). Experiments were carried out with a range of iron-oxide nanoparticles that were synthesized and surface-coated by our Chemical Engineering collaborators. The numerical method was improved to be volume conserving, and extended to 3D, for more quantitative matching. The measurements of interfacial motion by PS-OCT confirm theoretical predictions of the frequency doubling and importance of material properties, such as the particle size, for the interface displacements. The relative densities of the fluid phase(air/aqueous and dodecane/aqueous) strongly affect the interfacial displacement. Next, the acoustic responses to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Subsequently, the PS-OCT displacements in response to the external magnetic oscillation, from the rock samples into which different aqueous dispersions of nanoparticles were injected, were also measured in terms of the magnetic frequency, nanoparticle concentration, and other process parameters. Conclusions and the recommendations for further study are then given. / text

Multi-walled carbon nanotubes (MWCNTs) and integrated MWCNTs/ SiO2 nanoparticles (NPs) were loaded as additives into nanocomposite polyvinylidene fluoride (PVDF) membranes fabricated via phase inversion methods, and the effects of these additives on the structure and vacuum membrane distillation (VMD) performance of the membranes have been studied. With an appropriate amount of MWCNTs (2 wt.% to PVDF) blended into the membrane, VMD performance of membrane was improved significantly due to higher membrane porosity, contact angle and surface roughness without extreme compromise of liquid entry pressure of water (LEPw), which could reach up to 72 psi. Further integration of MWCNTs with a small amount of SiO2 nanoparticles (NPs) showed a synergic effect resulting in further improvement of VMD flux due primarily to the increase in surface pore size. When the amount of SiO2 NPs additive was large, the effects of NPs dominates the VMD performance. However, the asymmetric structure of PVDF membrane disappears, which exercises an unfavourable effect on VMD performance. All fabricated membranes exhibited a great desalination potential with extremely high salt rejection (>99.98%). The incorporation of MWCNTs did not improve the tensile properties of the membrane.

Membranas à base de polímeros perfluorosulfonados, como a Nafion, vêm sendo extensivamente usadas como membrana de troca protônica em células a combustível (FC). O objetivo deste trabalho foi desenvolver membranas eletrólito à base de polindeno sulfonado (SPInd) e poli(fluoreto de vinilideno) (PVDF), para uso como membranas de troca protônica em condições semelhantes às da membrana Nafion. As membranas foram preparadas por casting em diferentes composições utilizando PVDF como reforço mecânico e PVDF sulfonado (SPVDF) como agente compatibilizante. Todas as membranas foram avaliadas por análise termogravimétrica, calorimetria exploratória diferencial, análise dinâmico mecânica, microscopia eletrônica de varredura, grau de inchamento, capacidade de troca iônica e espectroscopia de impedância eletroquímica. As membranas com características semelhantes à membrana Nafion foram avaliadas em protótipo de FC a 80 °C. A membrana SPInd50/PVDF e as membranas com agente compatibilizante apresentaram condutividades iônicas na ordem de 10-2 S/cm, comparáveis àquela da membrana Nafion. A membrana com melhor desempenho em protótipo de FC foi o SPInd/PVDFC12, preparado com 50% de SPInd, 47,5% de PVDF e 2,5% de SPVDF (p/p), cujos valores de potencial de circuito aberto e densidade de potência máximo foram de 1,02 V e 74,54 mW/cm2, respectivamente. Apesar da densidade de potência máxima ser inferior à da membrana Nafion (603 mW/cm2), a membrana SPInd/PVDFC12 apresenta potencial para uso como eletrólito em célula a combustível. / Perfluorosulfonic acid ionomer membranes, e.g. Nafion, have been extensively used as proton exchange membranes in fuel cells (FC) due to their high proton conductivity and good mechanical properties. The aim of this work was to develop electrolyte membranes based on sulfonated polyindene (SPInd) and poly(vinylidene fluoride) (PVDF) to be used in the same conditions as Nafion. Membranes were prepared by casting with different compositions using PVDF as mechanical reinforcement and sulfonated PVDF (SPVDF) as coupling agent. The produced membranes were evaluated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis, scanning electron microscopy, water uptake, ion exchange capacity and electrochemical impedance spectroscopy. The membranes with similar results to Nafion, were evaluated in a FC prototype at 80 °C. The membrane SPInd50/PVDF and all the membranes with coupling agent had ionic conductivity in the order of 10-2 S/cm, comparable to the Nafion´s. The polyelectrolyte with the best performance was the SPInd/PVDFC12 which was prepared with 50 wt% SPInd, 47.5 wt% PVDF and 2.5 wt% SPVDF, that reached an open circuit voltage of 1.02 V and maximum power density of 74.54 mW/cm2. Even though Nafion´s maximum power density was higher (603 mW/cm2), the SPInd/PVDFC12 membrane showed potential to be used as electrolyte in fuel cells.

Membranas à base de polímeros perfluorosulfonados, como a Nafion, vêm sendo extensivamente usadas como membrana de troca protônica em células a combustível (FC). O objetivo deste trabalho foi desenvolver membranas eletrólito à base de polindeno sulfonado (SPInd) e poli(fluoreto de vinilideno) (PVDF), para uso como membranas de troca protônica em condições semelhantes às da membrana Nafion. As membranas foram preparadas por casting em diferentes composições utilizando PVDF como reforço mecânico e PVDF sulfonado (SPVDF) como agente compatibilizante. Todas as membranas foram avaliadas por análise termogravimétrica, calorimetria exploratória diferencial, análise dinâmico mecânica, microscopia eletrônica de varredura, grau de inchamento, capacidade de troca iônica e espectroscopia de impedância eletroquímica. As membranas com características semelhantes à membrana Nafion foram avaliadas em protótipo de FC a 80 °C. A membrana SPInd50/PVDF e as membranas com agente compatibilizante apresentaram condutividades iônicas na ordem de 10-2 S/cm, comparáveis àquela da membrana Nafion. A membrana com melhor desempenho em protótipo de FC foi o SPInd/PVDFC12, preparado com 50% de SPInd, 47,5% de PVDF e 2,5% de SPVDF (p/p), cujos valores de potencial de circuito aberto e densidade de potência máximo foram de 1,02 V e 74,54 mW/cm2, respectivamente. Apesar da densidade de potência máxima ser inferior à da membrana Nafion (603 mW/cm2), a membrana SPInd/PVDFC12 apresenta potencial para uso como eletrólito em célula a combustível. / Perfluorosulfonic acid ionomer membranes, e.g. Nafion, have been extensively used as proton exchange membranes in fuel cells (FC) due to their high proton conductivity and good mechanical properties. The aim of this work was to develop electrolyte membranes based on sulfonated polyindene (SPInd) and poly(vinylidene fluoride) (PVDF) to be used in the same conditions as Nafion. Membranes were prepared by casting with different compositions using PVDF as mechanical reinforcement and sulfonated PVDF (SPVDF) as coupling agent. The produced membranes were evaluated by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis, scanning electron microscopy, water uptake, ion exchange capacity and electrochemical impedance spectroscopy. The membranes with similar results to Nafion, were evaluated in a FC prototype at 80 °C. The membrane SPInd50/PVDF and all the membranes with coupling agent had ionic conductivity in the order of 10-2 S/cm, comparable to the Nafion´s. The polyelectrolyte with the best performance was the SPInd/PVDFC12 which was prepared with 50 wt% SPInd, 47.5 wt% PVDF and 2.5 wt% SPVDF, that reached an open circuit voltage of 1.02 V and maximum power density of 74.54 mW/cm2. Even though Nafion´s maximum power density was higher (603 mW/cm2), the SPInd/PVDFC12 membrane showed potential to be used as electrolyte in fuel cells.

Tato práce se zabývá charakterizací nanovláken na bázi polyvinylidenfluoridu. Zaměření práce je na piezoelektrické vlastnosti vlákna, které jsou studovány metodou piezoelektrické silové mikroskopie. Takto byly měřeny dva typy odlišných vzorků, které se lišily v parametrech výroby. Odlišnosti vláken v jejich fázovém složení byly také zkoumány za využití Ramanovy spektroskopie a infračervené spektroskopie s Fourierovou transformací. Chemická analýza povrchu a jeho stavu proběhla pomocí rentgenové fotoelektronové spektroskopie. Různé uspořádání nanovláken spolu s jejich průřezem bylo pozorováno rastrovacím elektronovým mikroskopem za využití fokusovaného iontového svazku. Rovněž byla zkoumána smáčivost a kontaktní úhel povrchu vzorků s demineralizovanou vodou. Bylo zjištěno, že vyšší rychlost otáček válce během procesu elektrostatického zvlákňování má velmi významný vliv na jejich uspořádání a tím i na parametry ovlivňující tvorbu piezoelektrického jevu a dalších materiálových vlastností.

With the development of modern industrial engineering technology, increasing demands of multifunctional materials drive the exploration of new applications of electrical conductive polymer nanocomposites (CPNCs). Toward applications of smart materials, sensing performance of CPNCs has gained immense attention in the last decade. Among them, strain sensors, based on piezoresistive behavior of CPNCs, are of high potential to carry out structural health monitoring (SHM) tasks. Poly(vinylidene fluoride) (PVDF) is highly thought to be potential for SHM applications in civil infrastructures like bridges and railway systems, mechanical systems, automobiles, windgenetors and airplanes, etc. because of its combination of flexibility, low weight, low thermal conductivity, high chemical corrosion resistance, and heat resistance, etc. This work aimed to achieve high piezoresistive sensitivity and wide measurable strain ranges in carbon nanotube based poly(vinylidene fluoride) (PVDF) nanocomposites. Four strategies were introduced to tune the sensitivity of the relative electrical resistance change (ΔR/R0) versus the applied tensile strain for such nanocomposites. Issues like the influence of dispersion of multi-walled carbon nanotubes (MWCNTs) on initial resistivity of PVDF nanocomposites and conductive network structure of MWCNTs, as well as piezoresistive properties of the nanocomposites, were addressed when using differently functionalized MWCNTs (strategy 1). In addition, the effects of crystalline phases of PVDF, mechanical ductility of its nanocomposites and interfacial interactions between PVDF and fillers on piezoresistive properties of PVDF nanocomposites were studied. Using hybrid fillers, to combine MWCNTs with conductive carbon black (strategy 2) or isolating organoclay (strategy 3), piezoresistive sensitivity and sensing strain ranges of PVDF nanocomposites could be tuned. Besides, both higher sensitivity and larger measurable strain ranges are achieved simultaneously in PVDF/MWCNT nanocomposites when using the ionic liquid (IL) BMIM+PF6- as interface linker/modifier (strategy 4). The detailed results and highlights are summarized as following: 1. The surface functionalization of MWCNTs influences their dispersion in the PVDF matrix, the PVDF-nanotube interactions and crystalline phases of PVDF, which finally results in different ΔR/R0 and the strain at the yield point (possibly the upper limit of sensing strain ranges). As a whole, regarding to the fabrication of strain sensors based on PVDF/MWCNT nanocomposite, in contrast to pristine CNTs, CNTs-COOH and CNTs-OH, CNT-NH2 filled PVDF nanocomposites possess not only high piezoresistive sensitivity but also wide measurable strain ranges. Gauge factor, i.e. GF, is ca.14 at 10% strain (strain at the yield point) for the nanocomposites containing 0.75% CNTs-NH2. 2. Using hybrid fillers of CNTs and CB to construct strain-susceptible network structure (conductive pathway consisting of string-like array of CNTs and CB particles) enhances the piezoresistive sensitivity of PVDF nanocomposites, which is tightly associated with the CNT content in hybrid fillers and mCNTs/mCB. The best piezoresistive effect is achieved in PVDF nanocomposites with fixed CNT content lower than the ΦC (0.53 wt. %) of PVDF/CNT nanocomposites. 3. ΔR/R0 and possible sensing strain ranges of PVDF nanocomposites were tailored by changing crystalline phases of PVDF and PVDF-MWCNT interactions. Besides, the increase of the strain at yield point in PVDF nanocomposites filled by CNTs-OH is more obvious than that in the nanocomposites containing the same amount of clay and CNTs. The nanocomposite consisting of 0.25% clay and 0.75% CNTs-OH have ca. 70% increase of the strain at the yield point (17%) and the GF at this strain is ca. 14, while GF for the nanocomposite filled by only 0.75% CNTs-OH is ca. 5 at 10% strain. 4. IL BMIM+PF6- served as interface linker for PVDF and MWCNTs, which significantly increased the values of ΔR/R0 and strain at the yield point of PVDF nanocomposites simultaneously. Besides, this increases with increasing IL content. With the aid of IL, the dispersion of nanotube and toughness of the nanocomposites are greatly improved, but the electrical conductivity of the nanocomposites is decreased with the incorporation of IL, which is related to the IL modified PVDF-MWCNT interface connection or bonding. GF reaches ca. 60 at 21% strain (the strain at the yield point) for PVDF nanocomposites filled by 10% IL premixed 2%CNTs-COOH.

No description available.