Chemical sensors based on arrays of polymer-coated surface acoustic wave (SAW) devices are required for defense applications that provide a combination of sensitivity, selectivity, portability and response time. The primary challenge in the development of these polymer-based microsensors is the need to reproducibly deposit high quality, defect-free polymer coatings onto microelectrodes. Coating methods such as air brushing and solvent casting have proven unreliable and I have investigated the possibility of depositing polymer films on microelectrodes using electrostatic processing methods. In this work AC electrospraying was used to deposit nanoscale polymer films onto the surface of microelectrodes. The alternating polarity of the electric field eliminates surface charge accumulation and the polymers were deposited uniformly across both electrically insulating and conducting surface regions. In a different work, DC electrospraying was used to deposit patterned organic coatings onto the surface of microelectrodes. The surface of the microelectrode array consisted of an alternating pattern of insulating, grounded-metallic and ungrounded metallic regions, each with a width of 15µm. The charged particles were deposited only onto the grounded-metallic surface regions where there is an electrical path for charge dissipation. No polymer deposition was observed on the insulating or ungrounded-metallic regions due to the effects of surface charge accumulation. Also, I, DC electrodeposited organic molecules within the pores of ceramic film. Due to electrospraying, this film has a strong built-in electric field that induces Stark effect in the organic molecules, providing a unique new technology for bio and chemical sensing. Electrospinning has been used to produce polymer nanofibers with diameters ranging from a few microns to less than 100 nanometers. Due to mechanical oscillations of the electrically charged fibers during electrospinning, they are usually collected in the form of a non-woven mat without any significant fiber orientation. I have developed a new method for making highly aligned arrays of polymer nanofibers by using an AC coupled DC field to drive the electrospinning process. This new "biased AC electrospinning" method can be used to deposit aligned arrays of polymer nanofibers onto virtually any substrate. Potential applications of well-ordered nanofiber materials include tissue engineering, filtration, drug delivery and microelectronics.

The aim of the present work was to design and characterize novel encapsulation structures of interest in the development of functional foods. For this purpose, various biopolymer-based microencapsulation structures were obtained through different processing technologies, with an emphasis on electrospraying as an advantageous alternative to conventional microencapsulation techniques. Firstly, novel microencapsulation structures were produced from aqueous solutions and in mild conditions by electrospraying, using different biopolymers as encapsulation matrices. For this purpose, the processing conditions were optimized and the relationship between the feed solution properties and the morphology of the electrosprayed materials was studied. The developed microstructures were then used to microencapsulate model bioactive ingredients with different properties, including hydrophilic molecules, hydrophobic compounds and probiotic microorganisms. For the hydrophobic ingredients, different strategies were evaluated in order to disperse them within the aqueous biopolymer solutions, such as the preparation of emulsions and liposome dispersions prior to electrospraying. An in-line setup for the continuous mixing of liposomes with the biopolymer and their subsequent hybrid capsule formation was also developed by combining microfluidic and electrospraying technologies. For the probiotic microorganisms, the convenience of preparing the feed suspensions from fresh culture or freeze-dried bacteria, as well as the impact of adding a surfactant and a prebiotic carbohydrate to the formulation, were also evaluated. The performance of the proposed encapsulation systems was evaluated in terms of microencapsulation efficiency, stabilization of the bioactive ingredients against degradation under detrimental conditions and/or their impact on the bioaccessibility of the microencapsulated ingredients after in-vitro digestion. Spray-drying was also used to microencapsulate some of the bioactive ingredients, in order to compare the results obtained through electrospraying with a more conventional encapsulation technique and using different encapsulation matrices. Additionally, a novel concept of bio-inspired encapsulation was proposed in this thesis: the potential of intact plant cells isolated from potato tubers to bind phenolic compounds was explored, and the impact of starch gelatinization on the loading capacity of these proposed encapsulation vehicles was also assessed. Finally, the impact of microencapsulation in real food systems was also studied. Yoghurts and biscuits were enriched with a peptide hydrolysate and a green tea extract, respectively, and the stabilization effect of the protective matrices during food manufacturing was assessed. The consumers' acceptability of the enriched biscuits was also studied. / El objetivo de este trabajo fue el diseño y caracterización de nuevas estructuras de encapsulación de interés en el desarrollo de alimentos funcionales. Para ello, se obtuvieron distintas microestructuras de encapsulación biopoliméricas utilizando diferentes tecnologías de procesado, con especial hincapié en el electroesprayado como alternativa ventajosa a las técnicas de microencapsulación convencionales. En primer lugar, se desarrollaron nuevas microestructuras de encapsulación a partir de disoluciones acuosas y en condiciones suaves mediante la técnica de electroesprayado, utilizando diferentes biopolímeros como matrices de encapsulación. Para ello, se optimizaron las condiciones de procesado y se estudió la relación existente entre las propiedades de las disoluciones de partida y la morfología de los materiales electroesprayados obtenidos a partir de ellas. Posteriormente, se utilizaron las estructuras desarrolladas para microencapsular ingredientes bioactivos modelo con diferentes propiedades, incluyendo moléculas hidrofílicas, compuestos hidrofóbicos y microorganismos probióticos. En el caso de los ingredientes hidrofóbicos, se evaluaron diferentes estrategias para dispersarlos en las disoluciones poliméricas acuosas, como la preparación de emulsiones y de liposomas para su posterior procesado mediante electroesprayado. También se desarrolló un proceso en línea para mezclar los liposomas con el biopolímero y electroesprayarlos en continuo, combinando las tecnologías de microfluídica y electroesprayado. En el caso de los microorganismos probióticos, se evaluó también la conveniencia de preparar las suspensiones bacterianas a partir de cultivo fresco o de liófilos, así como el impacto de añadir un surfactante y un carbohidrato prebiótico a la formulación. El comportamiento de los sistemas de encapsulación propuestos se evaluó en cuanto a eficiencia de encapsulación, estabilización de los ingredientes bioactivos frente a condiciones de estrés y/o impacto sobre la bioaccesibilidad de dichos ingredientes tras un proceso de digestión in-vitro. También se utilizó la técnica de secado por pulverización para microencapsular alguno de los ingredientes bioactivos, con el fin de comparar los resultados obtenidos mediante electroesprayado con los de una técnica de encapsulación convencional, y utilizando diferentes matrices de encapsulación. Además, en esta tesis se propone un nuevo concepto de encapsulación bio-inspirada, basada en el potencial de células vegetales de patata intactas para unirse a compuestos fenólicos. Asimismo, se evaluó el efecto de la gelatinización previa del almidón presente en las células en la capacidad de carga de estos potenciales vehículos de encapsulación. Por último, se estudió el impacto de la microencapsulación en alimentos reales. Se enriquecieron yogures y galletas con un hidrolizado de péptidos y un extracto de té, respectivamente, y se estudió el efecto estabilizador de las microcápsulas durante el procesado de estos alimentos. También se estudió la aceptabilidad por parte de los consumidores de estas galletas enriquecidas. / L'objectiu d'aquest treball va ser el disseny i caracterització de noves estructures d'encapsulació d'interès en el desenvolupament d'aliments funcionals. Amb aquesta finalitat, es van obtenir diferents microestructures d'encapsulació biopolimèriques utilitzant diferents tecnologies de processat, amb especial èmfasi en el electrosprayat com a alternativa avantatjosa a les tècniques de microencapsulació convencionals. En primer lloc, es van desenvolupar noves microestructures d'encapsulació a partir de dissolucions aquoses i en condicions suaus mitjançant la tècnica de electrosprayat, utilitzant diferents biopolímers com a matrius d'encapsulació. Per a això, es van optimitzar les condicions de processament i es va estudiar la relació existent entre les propietats de les dissolucions de partida i la morfologia dels materials electrosprayats obtinguts a partir d'elles. Posteriorment, es van utilitzar les estructures desenvolupades per microencapsular ingredients bioactius model amb diferents propietats, incloent molècules hidròfiles, compostos hidrofòbics i microorganismes probiòtics. En el cas dels ingredients hidrofòbics, es van avaluar diferents estratègies per a dispersar-los en les dissolucions polimèriques aquoses, com la preparació d'emulsions i de liposomes per al seu posterior processat mitjançant electrosprayat. També es va desenvolupar un procés en línia per a mesclar els liposomes amb el biopolímer i electrosprayar-los en continu, combinant les tecnologies de microfluídica i electrosprayat. En el cas dels microorganismes probiòtics, es va avaluar també la conveniència de preparar les suspensions bacterianes a partir de cultiu fresc o de liòfils, així com l'impacte d'afegir un surfactant i un carbohidrat prebiòtic a la formulació. El comportament dels sistemes d'encapsulació proposats es va avaluar respecte a eficiència d'encapsulació, estabilització dels ingredients bioactius front a condicions d'estrès i / o l'impacte sobre la bioaccesibilitat d'aquests ingredients després de la seva digestió in-vitro. També es va utilitzar la tècnica d'assecat per polvorització per microencapsular algun dels ingredients bioactius, per tal de comparar els resultats obtinguts mitjançant electrosprayat amb els d'una tècnica d'encapsulació convencional, i utilitzant diferents matrius d'encapsulació. A més, en aquesta tesi es proposa un nou concepte d'encapsulació bio-inspirada, basada en el potencial de cèllules vegetals de creïlles intactes per unir-se a compostos fenòlics. Així mateix, es va avaluar l'efecte de la gelatinització prèvia del seu midó en la capacitat de càrrega d'aquests potencials vehicles d'encapsulació. Finalment, es va estudiar l'impacte de la microencapsulació en aliments reals. Es van enriquir iogurts i galetes amb un hidrolitzat de pèptids i un extracte de té, respectivament, i es va estudiar l'efecte estabilitzador de les microcàpsules durant el processat dels aliments. També es va estudiar l'acceptabilitat per part dels consumidors d'aquestes galetes enriquides. / Gómez Gómez-Mascaraque, L. (2017). Development and Characterization of Microencapsulation Systems for Bioactive Ingredients of Interest in the Development of Functional Foods [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/93344 / TESIS

Submitted by Gabriela Lopes (gmachadolopesufpel@gmail.com) on 2018-07-30T17:31:21Z No. of bitstreams: 1 tese.pdf: 5070792 bytes, checksum: e3c93d2e0995cdf58a61f24f273d2f40 (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2018-07-31T19:13:06Z (GMT) No. of bitstreams: 1 tese.pdf: 5070792 bytes, checksum: e3c93d2e0995cdf58a61f24f273d2f40 (MD5) / Made available in DSpace on 2018-07-31T19:13:06Z (GMT). No. of bitstreams: 1 tese.pdf: 5070792 bytes, checksum: e3c93d2e0995cdf58a61f24f273d2f40 (MD5) Previous issue date: 2018-06-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / A busca pela minimização do impacto ambiental pelos materiais sintéticos e alternativas naturais para conservação de alimentos, direciona as pesquisas para o desenvolvimento de embalagens biodegradáveis e bioativas. O objetivo desse trabalho foi desenvolver hidrogéis bioativos a base de amido de arroz incorporados com óleo essencial de alecrim. Amidos de arroz com diferentes teores de amilose, nativos e modificados por intercruzamento, e poli(álcool vinílico) foram utilizados para elaboração de hidrogéis via gelatinização alcalina e por aquecimento. O óleo essencial de alecrim (OEA) foi avaliado pela composição química e contra a ação das bactérias: Salmonella Typhimurium ATCC 14028, Escherichia coli O157:H7 NCTC 12900 e Pseudomonas aeruginosa ATCC 15442. O OEA foi encapsulado por electrospraying de uma emulsão de amido modificado pelo reagente anidrido octenil succínico (amido- OSA) com diferentes concentrações de etanol (20-40%, v/v) e OEA (20-50%, p/p). Para a elaboração dos hidrogéis bioativos uma emulsão de amido-OSA e OEA foi adicionada antes e após a gelatinização do amido. A absorção de água, perfil de análise em textura, morfologia e integridade estrutural dos hidrogéis foram avaliadas. A gelatinização alcalina permitiu obtenção de hidrogéis mais rígidos, insolúveis em água e com menor absorção de água em relação aos hidrogéis elaborados pelo método de gelatinização por aquecimento. Estas características também foram influenciadas pelo teor de amilose do amido de arroz. As emulsões foram estáveis e apresentaram baixa tendência a agregação quando utilizado 20% de etanol. O electrospraying das emulsões permitiu a obtenção de cápsulas esféricas e com alta eficiência de encapsulação (82% a 98%). Com base nas propriedades dos hidrogéis, como integridade estrutural e resistência mecânica o amido de arroz modificado de média amilose foi escolhido para elaboração dos hidrogéis bioativos via gelatinização alcalina. Os hidrogéis bioativos apresentaram diferentes características dependendo da etapa de adição da emulsão, com maior absorção de água e menor dureza quando a emulsão foi adicionada antes da gelatinização. O óleo essencial de alecrim apresentou atividade antibacteriana contra S. Typhimurium ATCC 14028, E. coli O157:H7 NCTC 12900 e P. aeruginosa ATCC 15442. O. A ação dos hidrogéis com óleo essencial de alecrim contra proliferação dessas bactérias será foco de estudos futuros. / The aim of minimization of environmental impact by synthetic materials and natural alternatives for food preservation, leads the researches for the biodegradable and bioactive packaging development. The objective of this study was to develop bioactive hydrogels based on rice starch filled with rosemary essential oil. Native and crosslinked rice starches with different amylose contents, and poli(vinyl alcohol) were used to prepare hydrogels via alkaline- and heating-induced gelatinization. The rosemary essential oil (REO) had the chemical composition evaluated and antibacterial activities against Salmonella Typhimurium ATCC 14028, Escherichia coli O157:H7 NCTC 12900 e Pseudomonas aeruginosa ATCC 15442. The REO was encapsulated by electrospraying the emulsion of OSA-starch with different ethanol (20-40%, v/v) and REO (20-50%, w/w) contents. For bioactive hydrogels the OSA-starch/REO emulsion was added before and after the starch gelatinization. The water absorption, texture profile analysis, morphology and structure of the hydrogels were evaluated. The alkaline-gelatinization produced a more rigid, insoluble in water and with less water absorption hydrogel than the heating-gelatinization hydrogels. These amylose content also influenced the hydrogels properties. The 20% ethanol content emulsions were more stable and showed low tendency to aggregate than the others ethanol content emulsions. The electrosprayed emulsions formed spherical capsules with high encapsulation efficiency (82% to 98%). Based on the hydrogels properties, such as mechanical strength, the medium amylose modified rice starch was chosen for the bioactive hydrogels preparation via alkaline-gelatinization. Bioactive hydrogels presented different characteristics depending on the time the emulsion was added. When the emulsion was added before the gelatinization a higher water absorption and lower hardness was obtained. Rosemary essential oil presented antibacterial activity against S. Typhimurium, E. coli and P. aeruginosa. Rosemary essential oil presented antibacterial activity against S. Typhimurium, E. coli and P. aeruginosa. The bioactive hydrogels filled with REO activities against these bacteria will be further studied.

L’électrospinning est un procédé couramment utilisé pour la fabrication de membranes nanofibreuses non-tissées. Ces membranes sont particulièrement intéressantes pour des applications tels que l’ingénierie tissulaire et la libération contrôlée de médicaments car elles sont très poreuses et ont une large surface spécifique. Dans une première partie, nous avons développé une nouvelle stratégie afin de contrôler la morphologie et la dimension des fibres fabriquées par electrospinning. Puis nous avons développé un composite fait de nanofibres de PLA et de microparticules de PEG auto-organisé, créant des motifs en nid d’abeilles qui grandissent avec l’épaisseur de la membrane. Ces membranes auto-organisées ont une structure poreuse dont la dimension des pores va de quelques microns à plusieurs centaines de microns. Enfin, deux modèles ont été développés pour une libération contrôlée d’un composé model : la délivrance retardée par l’élaboration de structure sandwich et la libération directionnnelle par la création d’un gradient de concentration avec différentes cinétiques. / Electrospinning is widely used for the synthesis of nanofibrous non-woven membranes. The fabricated electrospun membranes have high porosity and high surface to volume ratio; they are thus suitable for many applications such as sensing, tissue engineering or drug delivery. In the present work, the first focus was on the fabrication of electrospun fibers with controlled morphology and dimension. Then A self-organized honeycomb-like composite made of simultaneously electrosprayed PEG microparticles and PLA electrospun fibers was developed. The obtained composite mat exhibits a hierarchical, porous structure with pore sizes ranging from few microns up to several hundreds of microns. Finally, a method tailoring the hydrophobicity of drug loaded nanofibrous membranes by the incorporation of electrosprayed PEG microparticles was developed.

Les structures poreuses tridimensionnelles fonctionnelles possèdent un fort potentiel dans de nombreuses applications biomédicales. Nous avons ainsi orienté nos travaux vers l'élaboration de nouveaux matériaux capables de répondre à plusieurs critères pour l'ingénierie tissulaire osseuse. Du fait de leur biodisponibilité, leur biocompatibilité et leur biodégradabilité, les poly(3-hydroxyalcanoate)s (PHAs) présentent des propriétés particulièrement adaptées pour ce type d'application. Dans un premier temps, nous avons développé de nouvelles stratégies contrôlées, rapides et aisées, de synthèse de copolymères à blocs à base de PHAs ainsi que de production d'oligoesters par activation sous micro-ondes. Par ailleurs, l'absence d'effet « non-thermique » des micro-ondes sur la polymérisation par ouverture de cycles du D,L-lactide a également été démontrée grâce à une investigation systématique. Dans un second temps, l'élaboration de divers matériaux tridimensionnels nanofibreux par électrofilage (« electrospinning ») a été réalisée afin de fabriquer des structures à base de PHAs de différentes morphologies avec la formation de fibres dans une large gamme de diamètres ou encore avec des topographies de surface contrôlées (nanopores ou rainures). Plusieurs stratégies de fonctionnalisation superficielle ont été également mises au point telles que le dépôt de nanoparticules d'hydroxyapatite selon un procédé original couplant les techniques de l' « electrospinning » et de l' « electrospraying », ou encore le « co-electrospinning » de la gélatine. De nouvelles approches de couplage covalent de molécules en surface des fibres de PHAs par chimie « click » ou par ouverture de fonctions époxyde préalablement introduites ont également été développées. Enfin, des investigations biologiques in vitro ont permis de mettre en lumière les potentialités de ces nouveaux matériaux nanofibreux comme supports de culture cellulaire à travers l'évaluation de l'adhérence, la prolifération et la différentiation de cellules souches mésenchymateuses humaines (hMSCs) pluripotentes vers un phénotype ostéoblastique / Functional three-dimensional porous scaffolds possess a high potential in many biomedical applications. We have thus oriented our work toward the elaboration of new materials able to meet several criteria for bone tissue engineering. Due to their renewability, their biocompatibility, and their biodegradability, poly(3-hydroxyalkanoate)s (PHAs) exhibit properties particularly suitable for this type of application. First, we have developed novel controlled strategies that are rapid and straightforward for the synthesis of PHA-based block copolymers as well as for the production of oligoesters upon microwave activation. Moreover, the absence of “non-thermal” microwave effect in the ring-opening polymerization of D,L-lactide was also demonstrated through a systematic investigation. Second, the elaboration of miscellaneous three-dimensional nanofibrous materials by electrospinning has been performed to produce PHA-based frameworks with different morphologies through the formation of fibers in a wide range of diameters or with controlled surface topography (nanopores or channels). Several strategies for surface functionalization have also been implemented, such as the deposition of hydroxyapatite nanoparticles by an original combination of the electrospinning and electrospraying techniques or by the co-electrospinning of gelatin. New approaches toward covalent coupling of molecules on the PHA fiber surface by “click” chemistry or by ring-opening of previously introduced epoxide groups have also been developed. Lastly, in-vitro biological investigations have highlighted the potential of these new nanofibrous materials as cell culture supports through the evaluation of the adhesion, proliferation, and differentiation of pluripotent human mesenchymal stem cells (hMSCs) toward an osteoblastic phenotype

L’administration d’aliments fonctionnels contenant des cellules probiotiques est une des voies de rétablissement de l'équilibre du microbiota. Pour assurer la protection des probiotiques pendant la transformation des aliments et le passage gastro-intestinal, l'encapsulation est essentielle. Nous proposons ici des supports hybrides à base de silice en tant que nouveaux systèmes d’encapsulation de probiotiques. Lactobacillus rhamnosus GG (LGG) a été choisi comme modèle de bactéries probiotiques et l'alginate comme polymère prébiotique. Deux types de supports ont été préparés, soit par émulsification, soit par électrospraying: (i) des billes hybrides de 10-30 μm dans lesquelles les bactéries étaient en contact direct avec un mélange d'alginate et de silice et (ii) des particules cœur-couronne de 200-600 μm dans lesquelles les bactéries sont d'abord encapsulées dans un gel d'alginate, puis recouvertes d'une couche de silice. La viabilité des LGG a été efficacement maintenue seulement dans les particules cœur-couronne, dans lesquelles LGG n’ont pas était directement exposées à la silice. Ces prototypes cargo ont permis la protection de LGG pendant le stockage dans la bière ou le jus de pomme, ainsi que pendant le passage à travers le tractus gastro-intestinal. En outre, les LGG libérées dans un écosystème fécal se sont multipliées au détriment des autres membres de la communauté de Lactobacilli. Cette étude offre donc une preuve de concept quant à la potentialité des systèmes hybrides silice/biopolymère pour l'administration orale de bactéries probiotiques / One way to reestablish the microbiota equilibrium is to administrate a functional food containing probiotic cells. To insure protection of the living matter during the food processing and the gastrointestinal passage, encapsulation is essential. Herein we propose silica-based hybrid carriers as new probiotic delivery systems. Lactobacillus rhamnosus GG (LGG) was chosen as a model probiotic bacteria and alginate as prebiotic polymer. Two types of carriers were prepared either by emulsification or by electrospraying: (i) hybrid beads of 10-30 m in which the bacteria was in direct contact with a mixture of alginate and silica and (ii) core-shell beads of 200-600 m in which the bacteria are first embedded in an aqueous core of alginate, then coated with a silica shell. The viability of LGG was efficiently maintained only in core-shell particles, in which LGG was not directly exposed to silica. Those core-shell prototype carriers allowed the protection of LGG during storage in beer or apple juice, and during the passage through the gastrointestinal tract. Additionally the LGG released in the colon outcompete other members of the Lactobacilli community and it was able to thrive within a fecal ecosystem. This study offers thus a proof of concept for the potential use of hybrid silica/biopolymer systems in oral delivery of probiotic bacteria

PVDF, Poly(vinylidene fluoride), is a polymer that has been studied for over four decades due to its good electromechanical properties, stability, and durability in various environments. Currently, PVDF is the only commercially available piezoelectric polymer. PVDF is a polymorph, which indicates the presence of several crystalline phases such as α, β, γ, and δ-phase. Oriented β-phase PVDF exhibits ferroelectric properties and displays the largest piezoelectricity amongst the four phases, which makes it the most desirable phase. Preparing oriented β-phase PVDF is a multi-step process, which is cost intensive, due to the time, labor and energy utilized. The main goal of this work is to prepare oriented β-phase PVDF using the electrospraying technique in a one step process. During the electrospraying process a polymer jet is ejected. This jet disintegrates into droplets due to overwhelming surface tension, resulting in a sprayed coating on the collector substrate. Because of the combination of jet ejection and the high voltage applied between the needle tip and the substrate, the droplets can be stretched and the polymer chains can be oriented. Both the stretching and the high electric field are required for the transformation of α-phase to the oriented β-phase. This study proposes that by using the electrospraying technique it is possible to transform the α-phase to the β-phase in a one step process starting from solution. This research focuses on the processing and characterization of electrosprayed PVDF as well as electrosprayed PVDF/carbon nanotubes (PVDF/CNT) nanocomposites. The specific tasks are to determine the changes to the PVDF phases due to the electrospraying technique, and to determine the changes in the PVDF morphology due to the addition of carbon nanotubes to the polymer matrix.PVDF with two different molecular weights were electrosprayed using different solvents and parameters. Initial observations after electrospraying were that, high boiling point solvents resulted in the spraying of the solution and forming films, whereas a low boiling point volatile solvent such as acetone resulted in the spinning of the solution thus forming non-woven fiber mats. The thermal and electrical properties of the electrosprayed PVDF and PVDF/CNT composites are measured using several characterization techniques, including Modulated Differential Scanning Calorimetry (MDSC), Dielectric spectroscopy, Thermally Stimulated Current (TSC), Fourier Transform Infrared Spectroscopy (FT-IR), and X-Ray Diffraction (XRD). MDSC results show that electrosprayed PVDF has a lower melting point temperature than that of PVDF commercially available pellets. In addition, electrosprayed PVDF/CNT nanocomposites show a linear increase in the percentage of crystallinity with the increase of CNT concentration in the composite. Dielectric spectroscopy results indicate that by increasing the CNT concentration in the composite, the dielectric constant and the polymer conductivity increase.From the four characterizing techniques used, two of them, FT-IR and XRD, show that it is possible to transform α-phase to β-phase PVDF in a one-step process using electrospraying. The other two techniques, TSC and dielectric spectroscopy, show α-phase for the electrosprayed samples without CNT, and some β-phase formation with samples electrosprayed with CNT. These last two techniques; TSC and dielectric spectroscopy have results that differ from the FT-IR and XRD techniques. This contradiction may be a result of the small amounts of β-phase in the sample, which cannot be detected using these techniques. Another reason may be due to the difference in the probing levels between these techniques. XRD and FT-IR probe at the molecular level, whereas TSC and dielectric probe at a much larger scale, which may make it hard to detect small amounts of β-phase.

No description available.

Electrospinning and electrospraying are electrohydrodynamic processes used for the fabrication of nano- and microfiber membranes and the deposition of particles on the membrane. Despite the numerous research papers found in the literature on electrospun polymers and their application in water treatment, not much is reported on the functionalization of electrospun nano- or microfibers and the deposition of ceramic nanoparticles on their surface by electrospraying. The use of these two processes may increase the efficiency of membranes in removing contaminants. In the present research, the processes of electrospinning and electrospraying are described and the factors affecting electrospinning are investigated. All parameters affecting the production of smooth NFs and NPs are discussed. A literature review of the recent advances in electrospinning and electrospray applications, as well as the application of NFs membranes in water treatment, has been described. This research has been designed based on the knowledge gaps identified in the literature. Detailed experiments were carried out on the preparation of PAN_P and Cs_P NFs membranes by electrospinning technique, the NFs membranes were then functionalized with different functional groups. The membranes were used for removal (Chapter 3) and degradation (Chapters 4 and 5) of dyes synthetic solutions. In the case of degradation, the membranes were electrosprayed with TiO2 NPs. All membranes were characterized by standard spectroscopic, microscopic, surface analytical, and thermal methods. Adsorption of MB, RB, and ST from a synthetic aqueous solution on the membranes PAN and EA-g-PAN NFs decreased in the order PAN<EA-g-PAN. The adsorption isotherm for the dyes fitted well with the models of Langmuir and Freundlich. The values of the correlation coefficient (r2) for Langmuir varied from 0.940 to 0.995 and for Freundlich from 0.941 to 0.998. The slightly increased values of the correlation coefficient in the case of Freundlich indicate that condensation (physical adsorption) of dyes on the NFs membranes also occurred in addition to the formation of monolayers. PAN_P NFs membranes prepared by electrospinning were functionalized with DETA to produce a functionalized PAN _F NFs membrane. TiO2 NPs synthesized in the laboratory were anchored to the surface of the PAN_F NFs membrane by electrospray to prepare PAN _Coa. A second PAN_Co was prepared by embedding TiO2 NPs into the PAN_P NFs by electrospinning. A similar strategy was also used for the Cs and TiO2 NPs system. The PAN_Coa NFs membrane was used for the degradation of MO while the Cs_Coa NFs membrane was used for the degradation of MB. The higher photocatalytic activity of PAN _Coa NFs membranes (92%, 20 ppm, and 99.5%, 10 ppm) compared to PAN_Co NFs membranes (41.64%) was due to the smaller band gap, high surface roughness, and large surface area. Also, the higher photocatalytic activity of the Cs_Coa NFs membrane (89%) compared to TiO2/Cs composite (Cs_Co) NFs membranes (40%) was due to a balance between the band gap, high surface roughness, and lower surface area. BET showed that the isotherms and hysteresis were similar for all NFs membranes, and they were classified as isotherm type IV and hysteresis H3 (IUPAC), corresponding to mesopores and slit-shaped pores.

Thesis (MEng) -- Stellenbosch University, 2014 / ENGLISH ABSTRACT: The electrodynamics of arbitrary, point-to-plane electrospraying geometries, were investigated in this research both analytically and numerically. Electrospraying is the process during which particles of sizes in the nanometre range are simultaneously generated and charged by means of an applied electrostatic field. A high electrostatic potential is applied to a conductive capillary needle, which overcomes the force exerted by the liquid surface tension. One of the primary limitations of this process are corona discharges. The effect of corona discharges have not been studied quantitatively, even though it is frequently reported in the electrospraying literature. The main objective of this research was to understand the corona discharge thresholds associated with electrospraying. Previously, only one theoretical, and two empirical investigations studied this phenomenon, over a time period of approximately forty years. It was clear that by better understanding these thresholds, electrospraying could be applied much more effectively. A corona discharge threshold model is proposed, using either a numerical or analytical model for the calculation of polarization fields. When compared with the experimental results of other researchers, both these two models have average relative percentage errors of approximately 15%. These are the first models proposed in the literature for the calculation of electrospraying corona thresholds. A new method to determine surface tension using electrospraying is described theoretically. In addition to this method, the calculation of corona discharge thresholds have various applications. For example, the dynamics of electrostatic ion thrusters are much better described, powder production by means of electrospraying can be optimised, and pattern generation using pulsed electrospraying cone-jets can be optimised as well. / AFRIKAANSE OPSOMMING: Die elektrodinamika van arbitrêre, punt-tot-vlak elektrosproei geometrieë was beide analities en numeries ondersoek in hierdie tesis. Dit is die proses waartydens nanodeeltjies gelyktydig gegenereer en elektrostaties gelaai word. Deur 'n hoë elektriese potensiaal aan te lê tot 'n geleidende kapillêr, is dit moontlik om die krag van die oppervlakte spanning te oorkom. Een van die primêre beperkings van elektrosproei is corona ontladings. Die effek van corona ontladings was nog nie kwantitatief bestudeer nie, selfs al word dit dikwels rapporteer in die elektrosproei literatuur. Die primêre doel van hierdie navorsing was om die corona ontlading drempels te verstaan wat geassosieer word met elektrosproei. In die verlede was daar nog net een teoretiese, en twee empiriese ondersoeke gewees wat hierdie verskynsel bestuur het, oor 'n tydperk van ongeveer veertig jaar. Dit was duidelik dat deur 'n beter begrip te hê van hierdie elektrosproei drempels, kan hierdie proses baie meer doeltreffend toegepas word. In hierdie tesis word 'n corona ontlading drempel model voorgestel, wat gebruik maak van 'n analitiese of numeriese model om die polarisasie velde te bereken. Wanneer vergelyk met die resultate van ander navorsers, het beide die modelle 'n gemiddelde relatiewe persentasie fout van ongeveer 15%. Hierdie is die eerste modelle wat voorgestel word vir die berekening van corona ontlading drempels. Deur gebruik te maak van elektrosproei, word 'n nuwe metode ook voorgestel om die oppervlakte spanning te bereken. In byvoeging tot hierdie, het die berekening van corona ontlading drempels vele ander toepassings. As 'n voorbeeld, die dinamika van elektrostatiese ioon stuwers word beter beskryf, en poeier produksie deur middel van elektrosproei kan optimeer word.