Water and CO adsorptions were studied over the stoichiometric and the oxygen-deficient Cu₂O(111) surfaces, using thermal desorption spectroscopy (TDS), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). Water is the only desorbing species detected in TDS and the extent of dissociation is unaffected by the surface condition: ≃ 0.25 monolayers of water dissociate on Cu₂O(111) regardless of surface condition. The local defect environment around oxygen vacancies does not play a significant role in the activity of the Cu₂O(111) surface for the dissociation of water. CO is found to bind molecularly to the surface through the carbon atom and with a heat of adsorption of 22 kcal/mol, higher value than that of CO on Cu₂O(100) (16.7 kcal/mol). This suggests that the local geometry of adsorption sites may play an important role in the way CO binds to Cu₂O surfaces. Electronic changes upon CO adsorption and the higher heat of adsorption indicate an increased σ-donor character for CO, with some π-backbonding interactions. The local defect environment around oxygen vacancies does not appear to affect CO adsorption on Cu₂O(111) surfaces. / Master of Science

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In this study, the use of surfactants, plate-like clays, organophilic molecules and side-chain crystallinity was investigated for their impact on the transport mechanisms of water vapour through polymer films. A model polymer latex, poly(styrene-co-butyl acrylate), was prepared using miniemulsion polymerization. Three different types of surfactants, sodium dodecyl benzene sulfonate (SDBS, an anionic surfactant), octyl phenol ethoxylate (OPE, a nonionic surfactant) and dodecyl ammonium- 3-butenoate (DA3B, a reactive surfactant) were used to stabilize the latex. Films were prepared from the resultant latices and their water vapour sorption behaviour determined across a water vapour partial pressure range of 0.1 to 0.9. Sigmoidal kinetic behaviour was seen for all three films, with the DA3B stabilized film exhibiting high diffusion coefficients compared to films stabilized with SDBS and OPE. The thermodynamic behaviour of the films differed and was dependent on the reactivity of the surfactant. SDBS and OPE stabilized films exhibited Flory- Huggins behaviour, while the DA3B stabilized film followed Henry’s Law. Despite significant differences in terms of these properties, the permeability coefficients were similar for the three films across the water vapour partial pressure range evaluated. The impact of sodium montmorillonite (Na-MMT) clay and an organophilic modifier, 2- acrylamido-2-methylpropanesulfonic acid (AMPS), on the water vapour sorption properties of poly(styrene-co-butyl acrylate) was evaluated. These polymer clay nanocomposites (PCNs) were synthesized using miniemulsion polymerization. The resultant latex films were characterized and used for water vapour sorption analyses. It was shown that complete exfoliation of the Na-MMT was necessary to minimize the equilibrium water vapour uptake. Even when Na-MMT was completely exfoliated, the amount of water vapour sorbed by the PCN was high and this was attributed to the hydrophilic nature of the clay. Using a least squares regression fit, good correlation was obtained between the experimental isotherms and the sorption behaviour predicted by the Dual Mode Sorption model which was originally developed for polymers in their glassy state. The impact of side chain crystallinity on the water vapour sorption properties of poly(methyl methacrylate-co-octadecyl acrylate) was evaluated. These random copolymers containing increasing amounts of octadecyl acrylate, and therefore increasing degrees of crystallinity, were synthesized using solvent polymerization. Although it could be expected that side chain crystallinity would be the main contributing factor resulting in a reduction in the diffusion coefficient, it was shown that the methyl group on the á- carbon of the vinyl group in the methacrylate reduced the diffusion to a greater extent through the increased stiffness of the polymer backbone. This was also reflected in poly(methyl methacrylate-co-octadecyl acrylate) having a greater activation energy for diffusion compared to polyoctadecyl acrylate. / AFRIKAANSE OPSOMMING: In hierdie studie is die gebruik van sepe, plaatagtige kleie, organofiliese molekules en sykettingkristalliniteit ondersoek ten opsigte van die impak op transportmeganismes van waterdamp deur polimeerfilms. ‘n Model polimeerlateks, polistireen-ko-butielakrilaat, is voorberei deur miniemulsiepolimerisasie. Drie verskillende tipes sepe, natriumdodekielbenseensulfonaat (NDBS, ‘n anioniese seep), oktielfenoletoksilaat (OFE, ‘n nie-ioniese seep) en dodekielammonium-3-butenoaat (DA3B, ‘n reaktiewe seep) is gebruik om die lateks te stabiliseer. Films is van die resultante lateks voorberei en hul waterdampsorpsie –eienskappe oor die parsiële waterdampdrukreeks van 0.1 tot 0.9 bepaal. Sigmodale kinetiese gedrag is vir al drie films waargeneem, met die DA3B gestabiliseerde film wat hoër diffusiekoëffisiënte toon in vergelyking met die films wat met NDBS en OFE gestabiliseer is. Die termodinamiese gedrag van die films het verskil en was afhanklik van die reaktiwiteit van die seep. NDBS en OFE gestabiliseerde films het Flory-Huggins gedrag getoon, terwyl die DA3B gestabiliseerde film Henry se Wet gevolg het. Ten spyte van die beduidende verskille ten opsigte van hierdie eienskappe was die permitiewe koëffisiënte soortgelyk vir die drie films regoor die parsiële waterdampdrukreeks wat vir die evaluasie gebruik is. Die impak van natriummontmorilloniet (Na-MMT) klei en ‘n organofiliese modifiseerder, 2- akrielamido-2-metielpropaansulfoonsuur (AMPS), op die waterdampsorpsie-eienskappe van polistireen-ko-butielakrilaat is geevalueer. Hierdie polimeer-klei-nanosaamgesteldemateriale (PKNe) is gesintetiseer deur van miniemulsiepolimerisasie gebruik te maak. Die resultante lateksfilms is gekarakteriseer en gebruik vir waterdampsorpsie analises. Daar is getoon dat algehele afskilfering van die Na-MMT nodig was om die ewewigswaterdampopname te minimaliseer. Selfs wanneer Na-MMT algeheel afgeskilfer was, was die hoeveelheid waterdamp gesorbeer deur die PKN hoog en kan dit toegeskryf word aan die hidrofiliese karakter van die klei. Deur ‘n kleinste-kwadrate-regressie passing te doen, is ‘n goeie korrelasie verkry tussen die eksperimentele isoterme en die sorpsie gedrag voorspel deur die Dubbelmodussorpsiemodel wat oorspronklik ontwikkel is vir polimere in hul glasagtige toestand. Die impak van sykettingkristalliniteit op die waterdampsorpsie-eienskappe van poli(metielmetakrilaat-ko-oktadekielakrilaat) is ondersoek. Hierdie ewekansige kopolimere wat toenemende hoeveelhede oktadekielakrilaat, en dus toenemende grade van kristalliniteit bevat, is gesintetiseer deur van oplossingspolimerisasie gebruik te maak. Alhoewel dit te wagte was dat sykettingkristalliniteit die hoofbydraende faktor is in die redusering van die diffusiekoeffisiente, is daar getoon dat die metielgroep aan die α-koolstof van die vinielgroep in die metakrilaat die diffusie tot 'n groter mate gereduseer het deur toenemende styfheid van die polimeerrugraat. Dit is ook gereflekteer deur poli(metielmetakrilaat-ko-oktadekielakrilaat) wat 'n groter aktiveringsenergie vir diffusie het in vergelyking met polioktadekielakrilaat.

Orientador: Fernando Galembeck / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-16T12:34:45Z (GMT). No. of bitstreams: 1 Gouveia_RubiaFigueredo_D.pdf: 6255414 bytes, checksum: b9783ee801d3d18f57579c596a700bab (MD5) Previous issue date: 2010 / Resumo: Os fenômenos eletrostáticos e suas consequências são familiares para a maioria das pessoas, mas o conhecimento sobre este tópico ainda é bastante empírico. Persistem grandes dificuldades na correlação de idéias fundamentais da teoria atômico-molecular com observações experimentais da eletrostática de materiais isolantes. A hipótese explorada nessa tese é: a atmosfera é uma fonte de cargas elétricas em isolantes, devido à partição de grupos OH- e H+ associados à adsorção de água. Logo, interações específicas entre íons presentes na água e sólidos isolantes contribuem para os padrões de cargas. Neste trabalho foram analisados padrões eletrostáticos em uma superfície de sílica recoberta por eletrodos de ouro produzidos por técnicas microlitográficas e partículas amorfas de fosfato de alumínio e sílica de Stöber utilizando a microscopia de força Kelvin (KFM) sob umidade relativa controlada. Os potenciais elétricos sobre a superfície de sílica dependem fortemente da umidade relativa, bem como da polarização dos eletrodos de ouro. A formação e dissipação dos padrões eletrostáticos são mais rápidas sob altas umidades. Já em baixas umidades a preservação dos potenciais elétricos é mais efetiva. Os potenciais elétricos das partículas de sílica e fosfato de alumínio são fortemente influenciados pela umidade relativa, sendo alterados mesmo em um ambiente completamente isolado eletricamente e aterrado. Os potenciais são modificados por eventos de adsorção e dessorção de água: sílica de Stöber torna-se mais negativa com o aumento da umidade, enquanto o fosfato de alumínio torna-se menos negativo, na ausência de qualquer ação de indução por um campo elétrico. Os resultados mostraram que a adsorção de água modifica os padrões de cargas de superfícies inorgânicas em escala nanométrica e que a eletroneutralidade não é uma característica geral de materiais isolantes. Neste trabalho também foram examinadas propriedades mecânicas de rigidez e adesão em nanoescala de partículas de fosfato de alumínio e dióxido de titânio, utilizando a microscopia de força pulsada digital (DPFM). As partículas apresentam uma grande heterogeneidade mecânica, mostrando domínios bastante diferenciados entre si. A nanoindentação da ponteira do AFM sobre as partículas mostrou que o dióxido de titânio apresenta maiores valores de rigidez, módulo de Young, força e energia de adesão e de histerese na deformação de suas superfícies. / Abstract: Electrostatic charging is familiar to most persons but knowledge on this topic is still rather empiric, mainly because fundamental ideas on the structure of matter are not well connected to the phenomenology of insulator charging. This thesis explores the following hypothesis: the atmosphere is as an electric charge reservoir for insulators, due to the partition of OH- and H+ groups associated to water adsorption. Thus, specific interactions between ions of adsorbed layers of water and insulating solids contribute to charge patterning. In this work, electrostatic patterning was examined in a silica surface partially covered with sets of interdigitated gold electrodes produced by microlithography techniques and also in aluminum phosphate and Stöber silica amorphous particles, using Kelvin force microscopy (KFM) under controlled relative humidity. Electric potentials acquired from the silica surface depend largely on the relative humidity as well as on the applied potentials at the gold electrodes. Pattern formation and dissipation are much faster under high relative humidity while the charged or discharged silica states are both more stable at low humidity. The electric potential measured along the surface of amorphous particles changes with relative humidity within an electrically shielded and grounded environment. Thus, water adsorption and desorption modify charge status of these particles: Stöber silica surface becomes more negative at higher humidity while aluminum phosphate becomes less negative, without any external electric potential or inductive input. These results show that water adsorption modifies charge status of inorganic surfaces and that electroneutrality is not a widespread characteristic of insulating materials. Another section of the thesis describes local nanomechanical stiffness and adhesion properties for aluminum phosphate and titanium dioxide particles, using digital pulsed force microscopy (DPFM). Aluminum phosphate and titanium dioxide particle domains present a large degree of heterogeneity. Aluminum phosphate particles are softer materials than titanium dioxide, undergoing greater nanoindentation of the AFM tip. On the other hand, titanium dioxide particle surfaces present larger stiffness, Young modulus, tipadhesion force, energy dissipated by hysteresis and detachment energy than aluminum phosphate particles. / Doutorado / Físico-Química / Doutor em Ciências

Alguns defeitos de qualidade podem causar alterações nos atributos da carne, dentre estes, podemos destacar as carnes PSE (Pale, Soft and Exudative). As carnes PSE são pálidas, flácidas e exsudativas ou molhada e resultam da queda brusca de pH enquanto a carcaça ainda encontra-se com temperatura elevada. A identificação de carnes PSE tem sido feita através da mensuração de pH e valor de L* (Luminosidade). No entanto, estudos sugerem que uma avaliação mais precisa da cinética do pH e decréscimo de temperatura precisa ser conduzida para entender melhor a etiologia das carnes PSE em aves. O objetivo deste trabalho foi obter a curva glicolítica para carnes normais e PSE de frango, através das análises de pH, L* e CRA (Capacidade de Retenção de Água). Este experimento foi realizado com carcaças obtidas em um abatedouro comercial (n=35), de linhagem Cobb, com 50 dias de idade, provenientes do mesmo lote de criação e com o mesmo tempo de jejum pré-abate (10h). As amostras de filés de peito foram obtidas das carcaças aleatoriamente coletadas imediatamente na saída do chiller de pré-resfriamento, sendo que as análises de pH, temperatura e valor de L*, foram conduzidas nas mesmas nos tempos de 1h35, 2h35, 3h35, 5h35, 8h35, 11h35, 14h35, 17h35, 20h35, 23h35 e 25h35 post mortem. As análises de CRA foram realizadas no tempo de 25h35 post mortem. As medições de pH indicaram que somente a partir do tempo de 8h35 post mortem foi possível verificar um indicativo de estabilização, sendo que o pH de carne PSE foi de 5,69±0,07, e para carne normal foi de 5,93±0,09. O valor final de pH (25h35 post mortem) foi de 5,98±0,06 e L* de 57,30±2,39 para carnes normais, já para carne PSE o resultado foi de 5,72±0,06 e L* de 59,44±1,51. Para CRA, a média das amostras (67,19±3,13 e 64,45±2,66) mostrou uma diferença entre os filés de frango normais e PSE respectivamente. Os dados encontrados neste trabalho estão de acordo com os relatados pelo próprio grupo de pesquisa em outro frigorífico e contradiz trabalhos similares, porém feitos em temperatura ambiente, indicando que para frangos sob condições comerciais a resolução do rigor mortis se dá após 8h35 post mortem. / Some quality defects can cause changes in attributes of the meat, among these we can detach the PSE meat (Pale, Soft and Exudative). The PSE meat is pale, flaccid and exudative and result from sudden pH decrease while the carcass is still under high temperature. The identification of PSE meat has been done by measuring pH and L* (Lightness). However, studies suggest that a more precise evaluation of the kinetics of pH and temperature decrease has to be conducted to better understand the etiology of PSE meat in poultry. The aim of this study was to obtain the glycolytic curve for normal and PSE meat of chicken, through the pH, L* and CRA (water holding capacity) analysis. This experiment was conducted with carcasses obtained from a commercial slaughterhouse (n = 35) of Cobb lineage, 50 days old, from the same batch of creation and with the same pre-slaughter fasting time (10h). Samples of breast fillets were obtained from carcasses randomly collected immediately at the output of pre-cooling chiller, and the analysis of pH, temperature and L * were conducted in the same in times 1h35, 2h35, 3h35, 5h35, 8h35, 11h35, 14h35, 17h35, 20h35, 23h35 and 25h35 post mortem. The CRA analyzes were performed at the time of 25h35 post mortem. The pH measurements indicated that only from the 04 time (8h35 post mortem) was possible to verify an indicative of stabilization, being that PSE meat pH was 5,69±0,07, and normal meat was 5,93±0,09. The final pH (25h35 post mortem) was 5,98±0,06 and L* 57,30± 2,39 for normal meat, while for PSE meat the result was 5,72±0,06 and L* 59,44±1,51. To CRA, the average of the samples (67,19±3.13 and 64,45± 2.66) showed a difference between the normal chicken fillets and PSE respectively. The data found in this study are consistent with those reported by own research group in another slaughterhouse and contradicts similar works, but made at room temperature, indicating that for chickens under commercial conditions the resolution of rigor mortis occurs after 8h35 post mortem.

Alguns defeitos de qualidade podem causar alterações nos atributos da carne, dentre estes, podemos destacar as carnes PSE (Pale, Soft and Exudative). As carnes PSE são pálidas, flácidas e exsudativas ou molhada e resultam da queda brusca de pH enquanto a carcaça ainda encontra-se com temperatura elevada. A identificação de carnes PSE tem sido feita através da mensuração de pH e valor de L* (Luminosidade). No entanto, estudos sugerem que uma avaliação mais precisa da cinética do pH e decréscimo de temperatura precisa ser conduzida para entender melhor a etiologia das carnes PSE em aves. O objetivo deste trabalho foi obter a curva glicolítica para carnes normais e PSE de frango, através das análises de pH, L* e CRA (Capacidade de Retenção de Água). Este experimento foi realizado com carcaças obtidas em um abatedouro comercial (n=35), de linhagem Cobb, com 50 dias de idade, provenientes do mesmo lote de criação e com o mesmo tempo de jejum pré-abate (10h). As amostras de filés de peito foram obtidas das carcaças aleatoriamente coletadas imediatamente na saída do chiller de pré-resfriamento, sendo que as análises de pH, temperatura e valor de L*, foram conduzidas nas mesmas nos tempos de 1h35, 2h35, 3h35, 5h35, 8h35, 11h35, 14h35, 17h35, 20h35, 23h35 e 25h35 post mortem. As análises de CRA foram realizadas no tempo de 25h35 post mortem. As medições de pH indicaram que somente a partir do tempo de 8h35 post mortem foi possível verificar um indicativo de estabilização, sendo que o pH de carne PSE foi de 5,69±0,07, e para carne normal foi de 5,93±0,09. O valor final de pH (25h35 post mortem) foi de 5,98±0,06 e L* de 57,30±2,39 para carnes normais, já para carne PSE o resultado foi de 5,72±0,06 e L* de 59,44±1,51. Para CRA, a média das amostras (67,19±3,13 e 64,45±2,66) mostrou uma diferença entre os filés de frango normais e PSE respectivamente. Os dados encontrados neste trabalho estão de acordo com os relatados pelo próprio grupo de pesquisa em outro frigorífico e contradiz trabalhos similares, porém feitos em temperatura ambiente, indicando que para frangos sob condições comerciais a resolução do rigor mortis se dá após 8h35 post mortem. / Some quality defects can cause changes in attributes of the meat, among these we can detach the PSE meat (Pale, Soft and Exudative). The PSE meat is pale, flaccid and exudative and result from sudden pH decrease while the carcass is still under high temperature. The identification of PSE meat has been done by measuring pH and L* (Lightness). However, studies suggest that a more precise evaluation of the kinetics of pH and temperature decrease has to be conducted to better understand the etiology of PSE meat in poultry. The aim of this study was to obtain the glycolytic curve for normal and PSE meat of chicken, through the pH, L* and CRA (water holding capacity) analysis. This experiment was conducted with carcasses obtained from a commercial slaughterhouse (n = 35) of Cobb lineage, 50 days old, from the same batch of creation and with the same pre-slaughter fasting time (10h). Samples of breast fillets were obtained from carcasses randomly collected immediately at the output of pre-cooling chiller, and the analysis of pH, temperature and L * were conducted in the same in times 1h35, 2h35, 3h35, 5h35, 8h35, 11h35, 14h35, 17h35, 20h35, 23h35 and 25h35 post mortem. The CRA analyzes were performed at the time of 25h35 post mortem. The pH measurements indicated that only from the 04 time (8h35 post mortem) was possible to verify an indicative of stabilization, being that PSE meat pH was 5,69±0,07, and normal meat was 5,93±0,09. The final pH (25h35 post mortem) was 5,98±0,06 and L* 57,30± 2,39 for normal meat, while for PSE meat the result was 5,72±0,06 and L* 59,44±1,51. To CRA, the average of the samples (67,19±3.13 and 64,45± 2.66) showed a difference between the normal chicken fillets and PSE respectively. The data found in this study are consistent with those reported by own research group in another slaughterhouse and contradicts similar works, but made at room temperature, indicating that for chickens under commercial conditions the resolution of rigor mortis occurs after 8h35 post mortem.