Orientadores: Edvaldo Sabadini, Munir Salomão Skaf / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-20T16:17:25Z (GMT). No. of bitstreams: 1 Cardoso_MarcusViniciusCangussu_D.pdf: 5363072 bytes, checksum: 77f8ee9c80c8ce3514b001281dfddae6 (MD5) Previous issue date: 2012 / Resumo: Soluções aquosas de mono, di, oligo, e polissacarídeos foram estudas nos níveis macroscópico e molecular, empregando-se enfoques termodinâmicos e espectroscópicos. A influência da intensidade da ligação de hidrogênio sobre a solubilidade dos carboidratos (lineares e cíclicos) mostrou-se fortemente dependente de suas solubilidades. Quanto menos solúvel o carboidrato, maior é o efeito da substituição isotópica do solvente (H2O por D2O). Este efeito sugere que carboidratos menos solúveis (e maiores) perturbam mais fortemente a estruturação das moléculas de água. Devido ao efeito cooperativo da transição coil-helix da k-carragena, o efeito isotópico sobre a gelificação é bastante intensificado. Segundo um perspectiva mais molecular, as taxas de troca protônicas, kb, entre os prótons da água e os grupos OH dos carboidratos dependem da natureza do açúcar, sendo os maiores valores observados para a forma linear, seguida pela forma piranosidea e por último pela forma furanosidea. Já as transferências de magnetização entre as populações de prótons da água e dos grupos CH-carboidratos são moduladas pelos movimentos moleculares e intermediadas pelas trocas protônicas com os grupos OH. Propõe-se que os prótons das moléculas de água interagem preferencialmente com os prótons OH e negligenciavelmente com os prótons CH. Estudos de relaxação H mostraram-se ricos para o estudo de processos moleculares de agregação micelar dos n-alquil-glicosídeos sendo possível demonstrar experimentalmente que a agregação leva a indisponibilização das hidroxilas ao interagirem com as moléculas de água / Abstract: Aqueous solutions of mono, di, oligo, and polysaccharides were studied on the macroscopic and molecular standpoints through thermodynamic and spectroscopic approaches. The effect of hydrogen-bonding strength on the solubility of a series of (linear and cyclic) saccharides showed to be strongly dependent of the solubility of the carbohydrate. As lower is the solubility of the carbohydrate, greater will be the deuterium isotopic effect of the solvent (H2O for D2O) on the carbohydrate solubilities. These results suggest that low soluble carbohydrates (and larger ones) perturb more strongly the water structure. Owing to the cooperativity of the coil-helix transition, the deuterium isotope effect on the gelling of k-carrageenan is intensified leading to stronger gels and double-helices more stable in D2O. Looking deeper onto a molecular perspective and based on spin-spin nuclear magnetic relaxation, the proton exchange rates, kb, between water and OH-carbohydrate, are dependent of the nature of the saccharide. The kb values are higher for linear than for pyranoside form, and the slowest value is found for fructofuranoside form. The transferring of magnetization between proton pools of water and CH-carbohydrates are modulated by molecular motions and intermediated by proton exchanging process between water and OH-carbohydrate protons. H NMR relaxation experiments of exchangeable protons provide to be rich in probing the micelar aggregation of n-alkyl-glucosides. It was possible to demonstrate experimentally that the aggregation of the surfactant molecules provoke a drastic reduction on the interactions between water and OH-saccharide head groups / Doutorado / Físico-Química / Doutor em Ciências

Cette thèse s’intéresse à la modélisation dynamique d’une pile à combustible (PàC) PEM en vue de son utilisation en électronique de puissance. Un modèle statique basé sur une expression de la tension en fonction du courant débité est tout d’abord présenté. Le modèle dynamique est élaboré ensuite. Il est montré que l’impédance électrochimique de diffusion-convection (Zd) s’apparente à une ligne de transmission de type RC. Une discrétisation en un nombre fini d’éléments a été effectuée. Afin d’obtenir un modèle simple, deux branches RC différentes sont considérées pour l’impédance Zd auxquelles sont ajoutées la capacité de double couche, les résistances de transfert et de la membrane. Ce modèle est validé sur deux PàC de 500 W et 5 kW sur une gamme de fréquence 5 mHz à 2 kHz, lors d’échelons de courant et lors du débit sur un hacheur élévateur. Il est montré que l’utilisation du découpage haute fréquence du convertisseur permet un diagnostic de l’état d’humidification de la membrane / This thesis deals with dynamic modelling of a proton exchange membrane fuel cell (PEMFC) with a view to integrate it into power electronics environment. Firstly a static model based on an expression that links current and voltage is presented. The dynamic model is then obtained. It is shown that the electrochemical diffusion-convection impedance (Zd) is similar to a RC transmission line. A discretization on a short number of elements is carried out. In order to obtain a simple model, two different RC branches for Zd impedance, a double layer capacitor, a transfer resistance, and a membrane resistance are considered. This modelling is validated on two 500 W and 5 kW PEMFC, for frequencies varying from 5 mHz to 2 kHz. The model is validated for both fuel cells during current step responses and operation with a boost converter. In this case it is shown how the high frequency switching of the converter can be used to obtain a diagnostic on the humidification state of the membrane