The present thesis entitled “Design and Synthesis of Novel Soft Composites from Physical Gels and Nanomaterials” deals with soft materials derived from low molecular weight gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular weight gel (LMOG) which forms the basis of the work. It delves with the history of research in physical gel field, design of different types of gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design new gelator molecules. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. The aspect of liquid crystallinity in the gel phase is also discussed to throw light on the pattern of assembly and potential uses of these materials. Towards the end there is a comprehensive discussion on the smart nanocomposites derived from LMOGs and nanomaterials. The design, synthesis and numerous applications of inorganic-organic hybrid composites are discussed. Chapter 2A describes the synthesis and characterization of a variety of fatty acid amides of different naturally occurring L-amino acids whose molecular structures are shown in Chart 2A.1. Some of them were found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, rheology and it was found that gelation was critically dependent on the fatty acid chain length and nature of the amino acid. Among them, L-alanine based gelators were found to be the most efficient and versatile as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. (Structural formula) Chart 2A.1. Molecular structures of various fatty acid amides of different amino acids. Chapter 2B describes efficient gelation of both aliphatic and aromatic hydrocarbon solvents by a fatty acid amide, n-lauroyl-L-alanine (Chapter 2B.1). In addition, this compound was found to gelate the binary solvent mixtures comprised of aromatic hydrocarbon e.g. toluene and aliphatic hydrocarbon e.g. n-heptane. SEM and AFM showed that the fiber thickness of the gel assembly increases progressively in the binary mixture of n-heptane and toluene with increasing percentage of toluene. The self- Chart 2B.1. Molecular structure of the gelator. assembly patterns of the gels in individual solvents, n-heptane and toluene are however, different. The toluene gel consists of predominantly one type of morphological species while n-heptane gel has more than one species leading to polymorphic nature of the gel. The n-heptane gel is thermally more stable than the toluene gel as evident from the measurement using differential scanning calorimetry. The thermal stability of the gels prepared in the binary mixture of n-heptane and toluene is dependent on the composition of solvent mixture. Rheology of the gels shows that they are shear-thinning material and show characteristic behavior of soft viscoelastic solids. For the gels prepared from binary solvent mixture of toluene and n-heptane, with incorporation of more toluene in the binary mixture, the gel becomes a more viscoelastic solid. The time sweep rheology experiment demonstrates that the gel made in n-heptane has faster gel formation kinetics than that prepared in toluene. Chapter 2C describes lyotropic mesophase formation by organogels of different fatty acid amides of L-alanine in aromatic solvents. The helical assembly, characteristic of the cholesteric mesophase was found to exhibit reflection bands in circular dichroism spectra. The reflection bands corresponded to the pitch of the helical arrangement of the gelator molecules in the aromatic solvent. Transmission Electron Microscopy (TEM) showed presence of twist in the gel fibres. Polarising optical microscopy of the organogel exhibited weak birefringence confirming lyotropic nature of the assembly. Chapter 3 deals with synthesis and characterization of a new class of molecules with molecular structures shown in Chart 3.1. Among a variety of amino acid based molecules only alanine and serine based molecules were found to form translucent gels in aliphatic hydrocarbons such as n-heptane. TEM showed presence of fiber like structures for alanine whereas serine based gelator produces unique network like structures. SEM of the dried gels exhibited presence of three dimensional fibrous networks to spongy globular cauliflower like structures depending on the molecular structure of the gelators. Rheological studies of the organogels showed that they behave like typical LMOG gels. The oscillatory rheological studies demonstrated that the L-serine based gelator, 5 formed more viscoelastic solid like gel than that of L-alanine based gelator, 1 in n-heptane. Chart 3.1. Molecular structures of different amino acid derivatives from 3,4,5-tri-dodecyloxybenzoic acid scaffold. Chapter 4A presents design and properties of new nanocomposites from LMOG and metal nanoparticles (Chart 4A.1). The profound influence of nanoparticle (NP) incorporation into physical gels was evident from various microscopic and bulk properties. The interaction of nanoparticles with the gelator assembly was found to depend critically on the capping agent coating the nanoparticles. TEM showed long range Chart 4A.1. Molecular structures of the gelator and various AuNPs synthesized. directional assembly of the certain AuNPs along the gel fibers. SEM of the dried gels and nanocomposites indicated that the morphological transformation in the composite microstructures depended profoundly on the capping agent of the nanoparticle. Differential Scanning Calorimetry showed that gel formation from sol postponed to lower temperature with incorporation of AuNPs having capping agents which were able to interact with the gel fibers. Rheological studies indicated that the gel-nanoparticle composites exhibit greater rigidity as compared to the naked gel only when the capping agents were able to interdigitate into the gelator assembly. Also, very low percentage of the AuNPs incorporation could switch the cholesteric mesophase of gel assembly, as evident from circular dichroism. We have been able to define a relationship between materials and molecular properties via manipulation of the molecular structures of NP capping agents. Chapter 4B discusses the design and preparation of novel organogel-carbon nanotube composites by incorporation of single-walled carbon nanotubes (SWNT) into physical gels formed by an L-alanine based Low Molecular Mass Organogelator (Chart 4B.1). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized (Chart 4B.1). Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon incorporation of SWNTs. The microstructures of nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of SWNT incorporation. Again, more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Also, the helical cholesteric mesophase formed by the toluene gel could be switched to a layer stacked assembly by doping functional SWNT. Remarkably, by using a near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting. Chart 4B.1. Molecular structures of the gelator and different functionalized SWNT synthesized. Chapter 5A presents design of two component hydrogels and their potential utilization as a template for metal nanoparticle synthesis. Among a variety of acids and amines (Chart 5A.1) only stearic acid or eicosanoic acid when mixed with di- or oligomeric amines in specific molar ratios form stable gels in water. The formation of such hydrogels depends on the hydrophobicity of the fatty acid, and also on the type of amine used. The gelation properties of these two component systems were investigated using electron microscopy, FTIR, 1H NMR spectroscopy, differential scanning calorimetry (DSC) and both single crystal and cast film X-ray diffraction. FTIR spectral analysis suggests salt formation during gelation. 1H NMR of the gels indicates that the fatty acid chains are immobilized in the gel state and when the gel is melted, these chains regain their mobility. Analysis of DSC data indicates that increase in spacer length in the di-/oligomeric amine lowers the gel melting temperature. Two of these gelator salts developed into crystals and structural details of such systems could be secured by single-crystal X-ray diffraction analysis. The structural information of the salts thus obtained was compared with the XRD data of the self-supporting films of those gels. Such analyses provided pertinent structural insight on the supramolecular interactions that prevail within these gelator assemblies. From the crystal structure it is confirmed that the multilayered lamellar aggregates exist in the gel and it also showed that only one plane of symmetry is present in the gel state. Finally, the hydrogel was used as a medium for the synthesis of silver nanoparticles. The nanoparticles were found to position themselves on the fibers and produce a long ordered assembly of gel-nanoparticle composite (Figure 5A.1). Chart 5A.1. Structures and abbreviations of different acids and amines checked for gelation. Figure 5A.1. TEM images of gel-Ag-NP composite. (a) Ag-NP synthesized in hydrogel of SA-IBPA (1:3.5), (b) Magnified images of Ag-NP preferentially residing on gel fibers. Chapter 5B demonstrates the aptitude of supramolecular hydrogel formation using simple bile acids e.g. lithocholic acid (LCA) in aqueous solution containing di- or oligomeric amines (Chart 5B.1). By variation of the choice of the amines in such mixture the hydrogelation properties could be modulated. However, replacement of LCA by cholic acid or deoxycholic acid resulted in no hydrogelation. FT-IR studies show that the carboxylate and ammonium residues of the two components are primarily involved in salt formation. This promotes further assembly of the components reinforced by continuous Chart 5B.1. Structures and abbreviations of different bile acids and amines checked for gelation. hydrogen bonded network leading to gelation. Electron microscopy shows that the morphology of the gels of two component systems which also depends strongly on the amine part. Variation of amine component from the simple ethanediamine (EDA) to oligomeric amine with lithocholic acid changes the morphology of the assembly from long one dimensional nanotubes to three dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines participate with the carboxylate and hydroxyl moiety through H-bonding and electrostatic forces. The rheological properties of this class of two component system provide clear evidence that this system is a shear-sensitive hydrogel and the flow behavior can be modulated varying the acid-amine ratio. From small angle neutron scattering study, it becomes clear that loose gel from LCA-EDA shows scattering oscillation due to the presence of non interacting nanotubules while for gels of LCA with oligomeric amine the individual fibers come together to form complex three dimensional structures of higher length scale.(For structural formula pl refer the pdf file)

Made available in DSpace on 2014-12-17T14:58:04Z (GMT). No. of bitstreams: 1 JoseAMN_DISSERT.pdf: 2578831 bytes, checksum: 78ca7925672b7876fad1b54e774b3827 (MD5) Previous issue date: 2010-12-30 / With the objective to promote sustainable development, the fibres found in nature in abundance, which are biodegradable, of low cost in comparison to synthetic fibres are being used in the manufacture of composites. The mechanical behavior of the curau? and pineapple leaf fibre (PALF) composites in different proportions, 25% x 75% (P1), 50% x 50% (P2) e 75% x 25% (P3) were respectively studied, being initially treated with a 2% aqueous solution of sodium hydroxide. Mechanical analyses indicated that with respect to studies of traction, for the combination of P1 and P3, better results of 22.17 MPa and 16.98 MPa, were obtained respectively, which are higher than that of the combination P2. The results of the same pattern were obtained for analysis of bending resistance where P1 is 1.21% and P3 represents 0.96%. In the case of resistance to bending, best results were obtained for the combination P1 at 49.07 MPa. However, when Young's modulus values were calculated, the values were different to the pattern of the results of other tests, where the combination P2 with the value of 4.06 GPa is greater than the other combinations. This shows that the PALF had a greater influence in relation to curau? fibre. The analysis of the results generally shows that in combinations of two vegetable fibers of cellulosic origin, the fiber which shows higher percentage (75%) is the best option than to the composition of 50%/50%. In the meantime, according to the results obtained in this study, in the case where the application should withstand bending loads, the better composition would be 50%/50% / Com o objetivo de promover o desenvolvimento sustent?vel, as fibras encontradas em abund?ncia na natureza, que s?o biodegrad?veis e de baixo custo quando comparado com as fibras sint?ticas, vem sendo utilizadas na aplica??o de produ??o de comp?sitos. Neste trabalho foi analisado o comportamento mec?nico ? partir do ensaio de tra??o e flex?o, em um comp?sito h?brido tendo como matriz uma resina sint?tica ortoft?lica refor?ada com fibras de curau? e fibras da folha de abacaxizeiro (PALF), nas propor??es de 25% x 75% (P1), 50% x 50% (P2) e 75% x 25% (P3), respectivamente, com as fibras de curau? e as fibras da folha do abacaxizeiro sendo tratadas quimicamente por uma solu??o aquosa de hidr?xido de s?dio (NaOH) com 8% de concentra??o. As an?lises mec?nicas indicaram que com rela??o aos estudos de tra??o, para a combina??o P1 e P3, foram obtidas melhores resultados de 22,17 MPa e 16,98 MPa, respectivamente, que ? maior que da outra combina??o de P2. Os resultados do mesmo padr?o foram obtidos para an?lise de flex?o onde P1 ? 1,21% e P3 de 0,96% que s?o maiores do que o resultado obtido da combina??o P2. No caso de resist?ncia ? flex?o, melhores resultados foram obtidos para a combina??o P1 de 49,07 MPa. Mas, quando foi calculado o m?dulo de Young, os valores foram diferentes do padr?o dos resultados dos outros testes realizados, com a combina??o P2 com o valor de 4,06 GPa que ? maior que das outras combina??es. Isto mostra que as fibras PALF tiveram uma influ?ncia maior com rela??o ? fibra de curau?. A an?lise dos resultados em geral demonstra que nas combina??es de duas fibras vegetais celul?sicas, uma ou a outra fibra com porcentagem maior (75%) ? a melhor op??o do que na composi??o de 50%/50%, entretanto no caso onde a aplica??o ser? para suportar cargas de flex?o, a melhor composi??o seria 50%/50%

[ES] El trabajo de investigación descrito en la presente Tesis Doctoral ha sido desarrollado en el marco del proyecto europeo MULTI2HYCAT (grant agreement N. 720783) y se ha centrado en la síntesis y caracterización de materiales mono- y multi-funcionales que presentan sitios catalíticos ácidos, básicos o redox. Diferentes líneas de investigación han sido desarrolladas en paralelo para obtener distintos materiales híbridos que serán empleados en diferentes procesos catalíticos, en línea con las necesidades de los socios industriales del proyecto. Debido a la naturaleza colaborativa del proyecto, cada miembro académico se ha en-centrado en un aspecto del desarrollo de los materiales. Es por ello que el Instituto de Tecnología Química (ITQ-CSIC), donde se ha llevado a cabo esta Tesis Doctoral, se ha centrado en la síntesis de los catalizadores híbridos. Por ello, parte de la caracterización descrita en el Capítulo 3 se ha llevado a cabo en la Università del Piemonte Orientale (IT), durante una estancia de un mes. Ademas, algúnos resultados catalíticos descritos en los Capítulos 3 y 5 han sido obtenidos por la University of Southampton (UK). En el Capítulo 3, se ha descrito la síntesis de dos catalizadores heterogéneos híbridos que presentan moléculas de ácido aril-sulfónico en su composición. En uno de ellos, el anillo aromático presentará átomos de flúor en posición 2, 3, 5, 6. Se han llevado a cabo dos estrategias de síntesis multi-etapas, a través de la síntesis de los precursores alkoxi-silanos, a través de procesos de condensación junto a un precursor de sílice (en ausencia de agentes directores de estructura, a pH neutro y temperaturas bajas) y de una reacción de tethering. Los materiales híbridos han sido caracterizados a través de dife-rentes técnicas. Las propiedades texturales, la estabilidad térmica y la composición química de los catalizadores ha sido estudiada. Además, moléculas sondas han sido adsorbidas en los materiales hibridos y las interacciones entre ellos han sido estudiadas a través de espectroscopias FTIR y RMN multi-nuclear. El catalizador hibrido en que el anillo aromático estaba fluorado resultó ser el más activo catalíticamente en la reac-ción de formación de acetal entre benzaldehído y etilenglicol. Una versión de los hí-bridos en que la superficie había sido pasivada con grupos metilos también fue obteni-da. Las propiedades de los materiales híbridos pasivados fueron comparadas, para po-der estudiar el efecto de la polaridad de la superficie del soporte sobre la actividad catalítica. En el Capítulo 4 se describe la síntesis de órgano-catalizadores híbridos obtenidos por anclaje de precursores de silicio funcionalizados con grupos básicos sobre un soporte del tipo MCM-41. Los catalizadores han sido caracterizados y empleados en diferentes reacciones de formación de enlaces C-C, como la condensación de Knoevenagel y la adición de Michael. Los catalizadores híbridos han sido empleados en la condensación entre furfural y metil isobutil cetona. El catalizador más activo ha sido seleccionado para ser funcionalizado posteriormente con nanoparticulas de paladio y empleado en un proceso catalítico en cascada. Mecanismos de reacción han sido pro-puesto para cada proceso catalítico. El efecto beneficioso debido a la presencia de los grupos silanoles en la superficie del soporte también fue analizado. En el Capítulo 5, la síntesis de catalizadores híbridos multi-funcionales fue descrita. Basándose en los resultados obtenidos en el Capítulo 4, se ha preparado un catalizador que presente grupos aminopropil- y nanopartículas de paladio. Las propiedades estructurales y texturales han sido estudiadas. Además, a través de la microscopia electrónica de transmisión, la distribución dimensional de las nanoparticulas ha sido estimada, resultando en un tamaño medio equivalente a la dimensión de los canales mesoporosos del soporte, MCM-4 / [CA] El treball de recerca descrit en aquesta tesi doctoral es va desenvolupar en el marc del projecte europeu MULTI2HYCAT (grant agreement N. 720783) i se centra en la sínte-si i la caracterització de catalitzadors híbrids mono i multifuncionals amb àcid, base o redox actius llocs. S'han desenvolupat diverses línies d'investigació en paral·lel per dissenyar múltiples catalitzadors híbrids per a diferents processos catalítics, basant-se en les necessitats dels socis industrials. A causa del caràcter col·laboratiu del projecte, cada soci acadèmic es va centrar princi-palment en un aspecte de tot el procés. Institut de Tecnologia Química (ITQ-CSIC), on es va desenvolupar aquesta tesi, està principalment centrat en el disseny i síntesi de catalitzadors híbrids. Per això, part dels resultats de caracterització reportats al Capítol 3 s'han dut a terme a la Università del Piemonte Orientale (IT), durant una estada d'un mes. Alguns dels resultats catalítics reportats al Capítol 3 i al Capítol 5 han estat reali-tzats per la Universitat de Southampton (Regne Unit). En el Capítol 3, s'ha descrit la síntesi de dos catalitzadors heterogenis híbrids que pre-senten molècules d'àcid aril-sulfònic en la composició. En un d'ells, l'anell aromàtic presentarà àtoms de fluor en posició 2, 3, 5, 6. S'han dut a terme dues estratègies de síntesi multi-etapes, a través de la síntesi dels precursors alkoxi-silans, mitjançant pro-cessos de condensació al costat d'un precursor de sílice (en absència d'agents directors d'estructura, a pH neutre i temperatures baixes) i d'una reacció de tethering. Els mate-rials híbrids han estat caracteritzats mitjançant diferents tècniques. Les propietats texturals, l'estabilitat tèrmica i la composició química dels catalitzadors ha sigut estudiada. A més, molècules sondes han estat adsorbides en els materials híbrids i les interaccions entre ells han estat estudiades mitjançant espectroscòpies FTIR i RMN multi-nuclear. El catalitzador híbrid en que l'anell aromàtic estava fluorat va resultar ser el més actiu catalíticament en la reacció de formació d'acetal entre benzaldehid i etilenglicol. Una versió dels híbrids en que la superfície havia estat pasivada amb grups metilos també va ser obtinguda. Les propietats dels materials híbrids passivats van ser comparades, per poder estudiar l'efecte de la polaritat de la superfície del suport sobre l'activitat catalítica. En el Capítol 4 es descriu la síntesi d'organo-catalitzadors híbrids obtinguts per ancoratge de precursors de silici funcionalitzats amb grups bàsics sobre un suport del tipus MCM-41. Els catalitzadors han estat caracteritzats i empleats en diferents reaccions de formació d'enllaços C-C, com la condensació de Knoevenagel i l'addició de Michael. Finalment, els catalitzadors híbrids han estat emprats en la condensació entre furfural i metil isobutil cetona. El catalitzador més actiu ha estat seleccionat per a ser funcionalitzat posteriorment amb nanoparticules de pal·ladi i emprat en un procés catalític en cascada. Mecanismes de reacció han estat proposat per a cada procés catalític. L'efecte beneficiós a causa de la presència dels grups silanols en la superfície de suport també va ser analitzat. En el Capítol 5, la síntesi de catalitzadors híbrids multi-funcionals va ser descrita. Basant-se en els resultats obtinguts en el Capítol 4, s'ha preparat un catalitzador que presenti grups aminopropil- i nanopartícules de palladi. Les propietats estructurals i texturals han estat estudiades. A més, a través de la microscòpia electrònica de trans-missió, la distribució dimensional de les nanoparticulas ha estat estimada, resultant en una grandària mitjana equivalent a la dimensió dels canals mesoporosos del suport, MCM-41. El material ha estat emprat com a catalitzador multi-funcional. / [EN] The research work described in this Doctoral Thesis was developed within the frame of the MULTI2HYCAT European Project (grant agreement N. 720783) and it is focused on the synthesis and characterization of mono- and multi-functional hybrid catalysts featuring acid, base or redox active sites. Several research lines have been developed in parallel to design multiple hybrid catalysts for different catalytic processes, building upon the needs of the industrial partners. Due to the collaborative nature of the project, each academic partners mainly focused on one aspect of the whole process. Instituto de Tecnología Química (ITQ-CSIC), where this Thesis was developed, mostly focused on the design and synthesis of the hybrid catalysts. For that, part of the characterization results reported in Chapter 3 have been carried out at Università del Piemonte Orientale (IT), during a one month stay. Some of the catalytic results reported in Chapter 3 and Chapter 5 have been car-ried out by the University of Southampton (UK). In Chapter 3 the synthesis of two different heterogeneous hybrid catalysts carrying aryl-sulfonic moieties, in which the aromatic ring was either fluorinated or not, is re-ported. Two multi-step synthetic approaches were developed, involving the synthesis of the silyl-derivative precursor, template-free one-pot co-condensation (at low tem-perature and neutral pH) and tethering reaction. A multi-technique approach was im-plemented to characterize the hybrid catalysts. Textural properties, thermal stability and chemical makeup of the materials were studied. Moreover, probe molecules were adsorbed onto the hybrids and the interaction were studied with multi-nuclear NMR and FTIR spectroscopies. The catalytic activity of the two hybrids showed superior performances for the fluoro-aryl-sulfonic acid, compared to the non-fluorinated mate-rial, in the acetal formation between benzaldehyde and ethylene glycol. Silanol-capped versions of the hybrids have also been prepared and their properties have been com-pared with those of hydrophilic hybrids, to study the effect of the polarity of the sur-face on the overall catalytic activity of the hybrids. In Chapter 4, the synthesis of hybrid mesoporous organocatalysts, obtained by graft-ing of commercial and custom-made silyl-derivatives onto MCM-41 supports, is re-ported. The hybrid catalysts were characterized and tested for different reactions in-volving C-C bond formation, such as Knoevenagel condensations and Michael addi-tion. Finally, the catalysts were tested in the condensation between furfural and methyl isobutyl ketone and the most performing catalyst was selected for the synthesis of a multi-functional hybrid. Reaction mechanisms have been proposed and the beneficial effect of the surface silanol groups on the catalytic activity was demonstrated. In Chapter 5, the synthesis of hybrid multi-functional catalysts is reported. Building upon the results reported in Chapter 4, a hybrid catalyst featuring aminopropyl moie-ties and palladium nanoparticles was developed. Structural and textural properties of the catalysts were accessed. Moreover, transmission electron microscopy showed a narrow nanoparticles distribution, centered a value equivalent to the size of the meso-porous channels of the support. The catalyst was tested in a tandem process involving the aldol condensation between furfural and methyl isobutyl ketone followed by hy-drogenation of the aldol adduct. The influence of several variables on the activity of the multi-functional catalyst was explored, with the scope of paving the way for more thorough studies to be carried out in flow regime. Lastly, proof-of-concept syntheses of multi-functional hybrid catalysts featuring base sites and supported metal complex are reported. / The research work described in this Doctoral Thesis was developed within the frame of the MULTI2HYCAT European Project (grant agreement N. 720783). I would like to thank la Caixa foundation for my PhD scholarship. / Erigoni, A. (2021). Organic-Inorganic Hybrid Catalysts for Chemical Processes of Industrial Interest [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/165238 / TESIS

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