The research herein focuses on the characterization of a PFCB/PVDF-HFP (70:30 wt:wt) blend fuel cell membrane including the constitutive and morphological properties, how these properties predict the stresses incurred under fuel cell operating conditions, and how these properties change over time under fuel cell operating conditions. Characterization was performed to mimic temperature and moisture conditions found in operating fuel cells to understand how these materials will behave in service.  This included thermal and hygral expansion, mass uptake, and the stress relaxation modulus.  These constitutive properties were chosen for characterization such that a model could be created to predict the stresses incurred during fuel cell operation, and examine how these stresses may change under different operating conditions and over time.  Based on the results of this model, lifetime predictions were made resulting in recommendations to further extend the operating time of this membrane beyond the DOE 5000 hr requirement. Stress predictions are useful, however if the material properties are changing over time under the fuel cell operating conditions, they may no longer be valid.  Therefore, PFCB/PVDF-HFP membranes were conditioned for different amounts of time under conditions similar to those commonly found in operating fuel cells.  These conditioned membranes were then characterized and compared with solvent exchanged membranes, the same materials used for previous material characterization.  The properties examined included stress relaxation modulus, bi-axial strength, mass uptake, water diffusion, and proton conductivity.  To further understand any changes noted in these properties after different environmental exposures, morphological analysis was performed.  This included small angle x-ray scattering, infrared spectroscopy, transmission electron microscopy, and differential scanning calorimetry. It was initially found that the proton conductivity decreased severely when the material was immersed at high temperatures over short time periods.  This was consistent with changes noted in other properties, and morphological analysis showed a decrease in the ionic network as well as an increase in the phase separation of the PFCB block copolymer as well as the PVDF-HFP crystallinity.  These large morphological changes could be very detrimental while in service, resulting in early termination of the fuel cell.  However, it was also noted that if these materials are annealed at high temperature (140"C), the negative property changes are abated.  This abatement is again tied to the morphology of the material, as annealing the material at high temperature creates stronger physical crosslinks, and induces a small amount of chemical crosslinking via condensation of the sulfonic acid groups, thus allowing the stress predictions performed earlier to have greater validity.   Therefore, it is important to not only understand the properties of a material during characterization, but also the underlying polymer structure, and how this structure can change over time, as all of these items control the long term material performance while in service. / Ph. D.

This study presents near-field electrospinning (NFES) on flat and hollow cylindrical process to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF)/ multi-walled carbon nanotube (MWCNT) piezoelectric nanofibers. Then the mechanical properties of fibers were measured. PVDF is a potential piezoelectric polymer material combining desirable mechanical, thermal, electrical properties with excellent chemical resistance. The existing researches mostly focused on piezoelectric thin film process. However, the research of characteristic about piezoelectric fiber is little. The methods of measurement of the mechanical properties (Young¡¦s modulus, hardness, and tensile strength¡Belongation) of the electrospun PVDF/MWCN composite nanofiber were carried out by using nano-indention test (MTS Nanoindenter Windows XP System) and tensile test (Microforce Testing System). By setting electric field (1¡Ñ107 V/m), rotating velocity (900 rpm) of the hollow cylindrical glass tube on a motion X-Y stage (2 mm/sec) and PVDF solution concentration (16 wt%), and MWCNT (0.03 wt%), in-situ electric poling, mechanical stretching and morphology of PVDF nanofiber were demonstrated. After the experiments of nano-indention test and tensile strength test, it is suggested that the good mechanical properties in NFES on cylindrical process. The results show that the mechanical properties of composite nanofiber are better than the conventional NFES process. The Young¡¦s modulus of 16% PVDF fiber prepared by cylindrical process is 0.89 GPa and hardness is 26.5 MPa. The mechanical properties were increased 56.2% and 49.4% after adding 0.03% of MWCNT, corresponding to 1.39 GPa and 39.6 MPa. The tensile strength was increased 32.7% and elongation at breaking point was increased 35% after adding 0.03% MWCNT.

In nature, microscopic surface textures impact useful function, such as the drag reduction of shark skin (Dean & Bhushan, 2010) and superhydrophobicity of the lotus leaf(Pan, Kota, Mabry, & Tuteja, 2013). In this study, we explore these phenomena by re-creating microscopic surface textures via the method of interfacial flow instability in drying polyvinylidene fluoride (PVDF) acetone solutions. In general, PVDF films can be made using either spin coating or electrospray deposition with various weight concentrations in acetone. In order to study the morphology of the porous structure of PVDF films, wet deposition samples were fabricated by spin coating or near-field electrospray. Possible theories are discussed and examined to explain the formation of these porous structures resulting in development of a well-controlled method to create porous PVDF films with various pore sizes and pore densities. All samples are characterized and found to exhibit superhydrophobicity and drag reduction. To connect porous PVDF film morphology to the established field of dry particle fabrication, PVDF particle synthesis by far-field electrospray is also reviewed and discussed. An established method to generate polymer particles of different morphologies in other polymers (Almeria-Diez, 2012) by electrospray drying is confirmed using PVDF as well. Due to the ability of scalable and re-configurable electrospray, the microscopic surface textures can be applied to areas of any size to reduce drag or impart water-repelling properties.

No description available.

På grund av det rådande miljöhotet så bör fokus för forskning och utveckling i ämnet riktas åt att utnyttja så många förnybara energikällor som möjligt, samt även optimera dessa för största möjliga energiupptagning. Vind, vatten och solljus är välkända och väl utformade källor för energi. Huruvida vatten i form av regn kan utnyttjas och dess potential kommer studeras i det här arbetet. Materialval och konstruktionslösningar står i centrum för arbetet. Vidare så studeras dess bakgrunder för utvinningsmetoderna och dess grundläggande principer tas upp för att skapa en bättre förståelse för möjligheterna att utnyttja tekniken. Fortsättningsvis så har rådande potentiella användningsområden och kommande utmaningar diskuterats utförligt. / Because of the prevailing environmental threat, focus for research and development in the subject should aim towards taking advantage of as many renewable energy sources as possible aswell as optimizing them to convert as much energy as possible. All renewable energy must be utilized, but above all, also optimized. Wind, water and sunlight are well-known and well-designed sources of energy. Whether water in the form of rain can be utilized and its potential as a sustainable commercial method will be studied in this paper. Material selection and design solutions are at the heart of the work. Furthermore, its backgrounds for the extraction methods are studied and its basic principles are addressed to create a better understanding of the possibilities of utilizing the technology. Moreover, the current potential uses and future challenges have been discussed in detail.

Les matériaux ferroélectriques présentant une permittivité diélectrique élevée et de faibles pertes diélectriques présentent un grand intérêt pour la réalisation de condensateurs et le stockage de l'énergie électrique. Les propriétés structurales et diélectriques influencent les paramètres ferroélectriques tels que la polarisation maximale du matériau Pm et la polarisation rémanente Pr sous l'effet d'un champ électrique appliqué Em. Ce mémoire propose d'étudier les propriétés structurales, diélectriques et ferroélectriques des céramiques dérivées de BaTiO₃ (BT) et SrTiO₃ (ST) ainsi que des films épais PVDF pur et composites tels que PVDF/BT et PVDF/BZT. Les céramiques ont été synthétisées par la méthode de la réaction solide et le procédé sol-gel. La substitution dans les sites-A ou les sites-B du matériau BaTiO₃ avec des cations tels que Ca ²⁺, Sr²⁺ and Zr⁴⁺ réduit la densité d'énergie électrique stockée Wd et augmente l'efficacité de stockage énergétique η. La céramique BaZr₀.₅Ti₀.₅O₃ (BZT0.5) présente l'efficacité de stockage énergétique la plus élevée (η=75%). La substitution dans les sites-A du matériau SrTiO₃ avec 40% de cations Ca²⁺ diminue la permittivité diélectrique (ε'∽200), mais cette permittivité est cependant plus stable sur une large gamme de fréquence [100 Hz-1 GHz]. La céramique Sr₀.₆Ca₀.₄TiO₃ préparée par voie sol-gel présente la densité d'énergie électrique stockée la plus élevée (Wd=0.149 J/cm³) sous l'action d'un champ électrique maximal élevé (Em=105 kV/cm). Les films épais à base de polymère PVDF ont été synthétisés par Spin-Coating. La permittivité diélectrique des films épais PVDF pur augmente avec l'apaisseur du film. L'incorporation de particules BT et BZT0.15 dans la matrice polymère PVDF augmente la permittivité diélectrique des films composites PVDF/BT (ε'=32 pour 30% de particules BT) et PVDF/BZT0.15 (ε'=32 pour15% de particules BZT). / Ferroelectric materials with a high dielectric permittivity and low dielectric losses are very attractive for the realization of capacitors and for electrical energy storage. To improve the electrical energy density Wd, the structural and dielectric properties influence the ferroelectric parameters such as the maximum polarization Pm and the remanent polarization Pr under an applied electric field Em. This manuscript proposes to study the structural, dielectric and ferroelectric properties of ceramics derived from BaTiO₃ (BT) and SrTiO₃ (ST) as well as pure PVDF thick films and composites such as PVDF/BT and PVDF/BZT. The ceramics were synthesized by the solid state reaction reaction route and the sol-gel process. The subsitution in the A-sites or B-sites of the BaTiO₃ material with cations such Ca²⁺, Sr²⁺ and Zr⁴⁺ reduces the electrical energy density Wd and increases the energy storage efficiency η. The ceramic BaZr₀.₅Ti₀.₅O₃ (BZT0.5) has the highest energy storage efficiency (η=75%). The substitution in the A-sites of SrTiO₃ material with 40% of Ca²⁺ cations reduces the dielectric permittivity (ε'∽200), but is more stable over a wide frequency range [100 Hz -1 GHZ]. The Sr₀.₆Ca₀.₄TiO₃ ceramic prepared by sol-gel process has the highest electrical energy density (Wd = 0.149 J/cm³) under an electrical field Em = 105 kV/cm. The PVDF thick films were synthesized by Spin-Coating. The dielectric permittivity of pure PVDF thick films increases when increasing the thickness. The addition of BT and BTZ0.15 particles in the PVDF polymer matrix increases the dielectric permittivity of the composite PVDF/BT thick films (ε'=32 for 30% of BT particles) and PVDF/BZT0.15 ones (ε'=32 for 15% of BZT particles).

No description available.

The beginning of this thesis contains an overview of properties of the insulators, and description of insulators that were used for in depth research of surface breakdown in vacuum. Furthermore, this work focuses on mechanisms of an electric breakdown initiation at the interface of the solid insulator and surrounding low pressure gas. Multiple methods for measurements of dielectric strength are examined. The experimental part describes the measurements performed in the vacuum chamber. The results of these measurements are then analysed. In conclusion, used insulators are compared and suggestions for further work are given.

Tato diplomová práce zkoumá flexibilní materiál k produkci elektřiny založený na piezoelektrickém polymeru Polyvinylidenfluorid (PVDF). Inkorporací piezoaktivní keramiky lze vlastnosti piezoelektrického polymeru PVDF významně zlepšit a převést na užitečnou elektrickou energii. PVDF byl vytvořen elektrostatickým zvlákňováním do vláken o tloušťce 1,5-0,3 µm a poté studován různými analytickými metodami. Tato práce nabízí popis elektrostatického zvlákňování, přípravu vzorků a teoretický úvod do analytických metod, kterým byly vzorky podrobeny. Morfologie a distribuce nanostrukturované keramiky do polymerní matrice PVDF byla pozorována použitím skenovací elektronové mikroskopie (SEM) a energiově disperzní spektroskopie (EDX). Pro tvorbu fáze a podrobné fázové složení byly vzorky charakterizovány infračervenou spektroskopií s Fourierovou transformací (FTIR). Práce také obsahuje analýzu s použitím Ramanovy spektroskopie, metody používané k identifikaci a porovnání chemických sloučenin. Elektrické vlastnosti byly studovány dielektrickou spektroskopií a je poskytnuta korelace se složením. Jednotlivé komponenty dotovaných vláken jsou charakterizovány a vyhodnocovány v souvislosti s jejich budoucím využitím v senzorech.

Poly(vinylidene fluoride) PVDF is a semi-crystalline fluoropolymer that attracted researchers' attention more than a decade ago due to its remarkable properties, such as mechanical strength, thermal stability, chemical resistance, good processability, and excellent aging resistance. Due to these excellent properties, PVDF is applied in many applications such as membranes and filtration, biomedical applications, drug delivery, batteries, energy generation, energy storage, sensors, actuators, and energy harvesting applications. The dissertation was inspired by PVDF’s outstanding properties and applications. First of all, the effect of chain topology of on the crystallization and polymorphism between linear and star PVDF homopolymers were studied. Well-defined linear and stars PVDF homopolymers architectures were synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerization. The non-isothermal crystallization study showed an increase in the amount of ferroelectric β-phase with respect to the paraelectric α-phase as the number of arms in the PVDF stars increases. This finding is explained by the increased topological complexity in the stars of several arms, which leads to the preferential formation of the less thermodynamically stable ferroelectric β-phase. Moreover, the isothermal crystallization kinetics of the PVDF stars was faster than the linear PVDF as a result of their speedier nucleation. Secondly, we report the synthesis of poly(n-isopropylacrylamide)-b-poly(vinylidene fluoride) (PNIPAM-b-PVDF), amphiphilic block copolymers with linear and star architectures by RAFT sequential living polymerization. Due to the presence of a lower critical solution temperature (LCST) for PNIPAM (coil-globule transition around 32 °C), the synthesized PNIPAM-b-PVDF block copolymers have thermo-responsive behavior, therefore, potential application in the fabrication of thermo-responsive membranes. All fabricated membranes by nonsolvent-induced phase separation (NIPS) method exhibited thermo-responsive behavior with water permeability and PEG rejection experiments. Moreover, the several heating-cooling cycles showed that the thermal-responsive behavior of these membranes are reversible and stable. Finally, a suggested potential future work is given to synthesize other PVDF-based block copolymers via sequential living polymerizations.