The air-water interface is abundant in the environment, thus it is an important proxy for atmospheric processes such as the uptake and transfer of molecules, heterogeneous reactions, photochemistry, and cloud condensation. This thesis aims to elucidate the role of semi-soluble and insoluble organic coatings on atmospheric processes at the air-water interface. Using glancing-angle LIF it was found that monolayer coatings of 1-octanol and of octanoic acid have opposing effects on the ozonation rate of pyrene at the air-water interface. LIF was also coupled with a Profile Analysis Tensiometer (PAT-1) to measure the effect of stearic acid coating compression on the uptake of HCl to a water droplet. Due to preliminary issues with this novel technique, no significant uptake suppression was observed. The oxidation of benzene by OH radical was also explored briefly, as were the photophysics of photosensitizers and the angle dependence of Raman signal from a D2O pendent droplet.

A series of detailed laboratory investigations were conducted to examine low solubility gas transfer across wind-forced wavy air-water interfaces. The study focuses on the increase in gas flux associated with the microphysical interfacial wind momentum exchange and the complex wave coupled hydrodynamics. Key elements of the laboratory investigations included the measurement of hydrodynamic behaviour within the aqueous viscous sub-layer using a particle image velocimetry (PIV) system and the development of a Laser Induced Fluorescent (LIF) system capable of measuring reliable dissolved oxygen concentration profiles to within 28??m of the air-water interface. Major achievements and findings included: 1. The first phase resolved gas flux measurements along wind forced microscale waves, indicating the highest mean gas fluxes are located in the wave troughs. This finding demonstrated the relative importance of wave orbital straining in gas flux enhancement; a wave coupled hydrodynamic process whose significance has previously been neglected. 2. The relative contributions to gas flux from wind shear, wave orbital straining, increased surface area of the waves, parasitic capillary ripples and microscale breaking are quantified with respect to friction velocity, wave steepness and an efficiency of microscale wave breaking. The parasitic capillary ripples are shown to have a negligible role in gas enhancement. A hybrid model is developed to estimate the gas flux based on both wind and wave characteristics. 3. Gas enhancement due to microscale wave breaking and the significance of the highly localised subduction at the toe of the spilling region on the leeward face of the wave crests was investigated using data from the LIF experiments. The highly localised subduction was shown to substantially reduce the thickness of the diffusion sub-layer, resulting in an increase in gas flux when waves transitioned from the incipient breaking to the microscale breaking wave form. 4. Consideration of previously unidentified optical distortions in LIF imagery due to non-linear effects is presented that is critical for robust LIF data processing and experimental design. A formal mathematical description of optical distortions has been developed and presented.

The surface behavior of biologically or atmospherically relevant chemical compounds in aqueous solution has been studied using surface-sensitive X-ray photoelectron spectroscopy (XPS). The aim is to provide information on the molecular-scale composition and distribution of solutes in the surface region of aqueous solutions. In the first part, the distribution of solutes in the surface region is discussed, where in particular single molecular species are studied. Concentration-dependent studies on succinic acid and various alkyl-alcohols, where also parameters such as pH and branching are varied, are analyzed using different approaches that allow the quantification of surface concentrations. Furthermore, due to the sensitivity of XPS to the chemical state, reorientation of linear and branched alkyl-alcohols at the aqueous surface as a function of concentration is observed. The results are further discussed in terms of hydrophilic and hydrophobic interactions in the interfacial region, where the three-dimensional hydrogen bonded water structure terminates. In the second part, mixed solutions of compounds, both ionic and molecular, are inspected. Again concentration, but also co-dissolution of other chemical compounds, are varied and differences in the spatial distribution and composition of the surface region are discussed. It is found that the guanidinium ion has an increased propensity to reside at the surface, which is explained by strong hydration in only two dimensions and only weak interactions between the aromatic π-system and water. Ammonium ions, on the other hand, which require hydration in three dimensions, are depleted from the surface region. The presence of strongly hydrated electrolytes out-competes neutral molecules for hydrating water molecules leading to an enhanced abundance of molecules, such as succinic acid, in the interfacial region. The partitioning is quantified and discussed in the context of atmospheric science, where the impact of the presented results on organic loading of aerosol particles is emphasized.

L’interface air-eau est un milieu où la tension de surface intervient en permanence pour minimiser l’énergie de la surface. Cette force est à l’origine des phénomènes capillaires que les organismes semi-aquatiques exploitent. L’objectif de cette thèse est d’étudier l’importance de ces phénomènes dans l’écologie des organismes semi-aquatiques en prenant les gyrins comme modèle. Les résultats montrent que le ménisque bipolaire produit par les gyrins est responsable d’auto-assemblables statiques entre individus immobiles. Les gyrins utilisent également différents types de nage pour minimiser les forces de résistance qu’ils rencontrent, notamment la force liée à la production d’onde. L’étude expérimentale de la perception d’objets immobiles suggère la perception des ménisques par les gyrins. L’écholocation grâce aux ondes de surface, supposée dans la littérature, ne peut cependant être exclue. / The surface tension at the air-water interface is responsible for capillary phenomena minimizing surface energies. Semi-aquatic organisms have evolved to exploit this capillarity. The purpose of this thesis is to study the importance of capillary phenomena in the ecology of semi-aquatic organisms using whirligig beetles as a model. Results show that the bipolar meniscus produced around whirligig beetles is responsible for static self-assembly between individuals. These insects use different types of swimming to minimize resistance forces, especially the wave drag. The experimental study of the detection of immobile objects suggests that whirligig beetles perceive the menisci. Echolocation using surface waves, assumed in literature, cannot however be excluded.

Submitted by DOUGLAS RICARDO DE ASSIS null (douglasnet9@hotmail.com) on 2016-03-10T00:50:50Z No. of bitstreams: 1 Dissertação de mestrado_Douglas Ricardo de Assis.pdf: 1652654 bytes, checksum: 93d244d8dfc88314c10a76a7d27326ef (MD5) / Approved for entry into archive by Sandra Manzano de Almeida (smanzano@marilia.unesp.br) on 2016-03-10T19:37:31Z (GMT) No. of bitstreams: 1 assis_dr_me_araiq_par.pdf: 232607 bytes, checksum: 0428ae381482be9888a3bad4adaa01cc (MD5) / Made available in DSpace on 2016-03-10T19:37:31Z (GMT). No. of bitstreams: 1 assis_dr_me_araiq_par.pdf: 232607 bytes, checksum: 0428ae381482be9888a3bad4adaa01cc (MD5) Previous issue date: 2016-02-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A auto-organização é uma das ferramentas mais versáteis e mais poderosas para a estruturação de nanopartículas em duas ou três dimensões. A técnica de Langmuir - Blodgett é o método mais promissor para a produção de filmes bidimensionais organizados de tensoativos, polímeros e nanopartículas (NPs), porque proporciona um bom controle da espessura e a homogeneidade da monocamada e de multicamadas. Esse trabalho visa sintetizar nanopartículas de Ag na interface ar-água utilizando filmes de Langmuir-Blodgett de surfactantes como suportes. A síntese das NPs de Ag na interface ar/água foi realizada de acordo com a metodologia de Khomutov e colaboradores. Foi possível sintetizar as NPs de Ag através do espalhamento da mistura das soluções de sulfadiazina de prata e ácido esteárico com razão molar de 1:1. As imagens de microscopia eletrônica de varredura de alta resolução mostram que a ausência de ácido esteárico melhorou a organização das NPs durante a síntese na interface ar/água. A composição química das NPs de prata foi determinada através da espectroscopia de energia dispersiva de raios X acoplada ao microscópio eletrônico operando no modo de varredura. Um estudo comparativo foi feito preparando-se filmes de NPs de Ag. As nanopartículas de Ag recobertas com dodecil sulfato de sódio foram sintetizadas de acordo com o método descrito por Song. As nanopartículas de Ag recobertas com polietilenoglicol (MM ≈ 3400 g.mol-1) e com ácido oléico/oleilamina foram sintetizadas pelo método poliol. Os difratogramas de raios X confirmaram a composição e a fase obtida em cada amostra. Foi estudada a composição do recobrimento das NPs através da espectroscopia na região do infravermelho e quantificado através das análises termogravimétricas. A preparação dos filmes LB de todas as amostras foi feita de acordo com o método descrito por Shin. Através das imagens de microscopia eletrônica de varredura de alta resolução observa-se que somente os filmes LB das nanopartículas de Ag recobertas com ácido oléico e oleilamina apresentam uma organização a longo alcance. Durante a formação dos filmes das amostras recobertas com SDS e com PEG3400 as nanopartículas agregaram prejudicando a organização do sistema. Esse processo de agregação pode ser atribuído a falta de surfactante na superfície das NPs ou ao excesso de polímero que aprisiona as nanopartículas no meio de suas cadeias carbônicas interferindo na organização de NPs. / Self-assembly is one of the most powerful and versatile tools for structuring nanoparticles in two or three dimensions. The Langmuir–Blodgett (LB) technique is the most promising method for production of organized surfactants, polymers, and nanoparticles (NPs) two-dimensional films, because it provides good control of the thickness and homogeneity of the mono and multilayer. This paper aims to synthesize silver nanoparticles in the air-water interface using surfactants Langmuir-Blodgett films such as “templates”. The synthesis of Ag NPs in the air / water interface was performed according the Khomutov methodology [1] it was possible to synthesize Ag NPs by spreading the mixture of silver sulfadiazine solutions and stearic acid molar ratio 1: 1. Field emission gun scanning electron microscope (FEG-SEM) images show that the absence of stearic acid improved the arrangement of NPs during synthesis in the air / water interface. The chemical composition of silver NPs was determined by energy dispersive X-ray spectroscopy attached to the electron microscope operating in scan mode. A comparative study was made preparing Ag NPs films. The Ag nanoparticles coated with sodium dodecyl sulfate were synthesized according to the method described by Song. The Ag nanoparticles coated with polyethylene glycol (MW ≈ 3400 g / mol) and oleic acid / oleylamine was synthesized by the polyol method. The X-ray diffraction confirmed the composition and phase obtained in each sample. It studied the composition of the coating of NPs through spectroscopy in the infrared region and quantified through thermogravimetric analysis. The preparation of LB films of a silver nanoparticles covered with oleic acid and olelamine (Ag@AO/OL) was done according to the methodology described by Shin et al. The images obtained by electron microscopy high resolution scan can be observed that only the LB films of Ag nanoparticles coated with oleic acid and oleylamine have an organization-reaching. During the formation of the films of the other samples the aggregated nanoparticles damaging the system organization. This aggregation process may be attributed to the lack of surfactant on the surface of the NPs or excess polymer which entraps the nanoparticles in the middle of their carbon chains interfering with NPs organization. / CNPq: 139251/2013-8

O objetivo global deste trabalho foi fornecer subsídios para melhor compreender como as políticas públicas voltadas às emissões veiculares, incluindo o uso de etanol combustível, podem afetar a composição química da atmosfera. O peróxido de hidrogênio (H2O2) é um dos oxidantes mais importantes presentes na troposfera, podendo participar de reações com uma variedade de compostos orgânicos e inorgânicos. Neste trabalho, a determinação de H2O2, etanol, acetaldeído e outras espécies orgânicas e inorgânicas, foi realizada na fase gasosa, água de chuva e em águas superficiais. Foi utilizado de forma pioneira o método fluorimétrico baseado na formação do fluoróforo 2,7-diclorofluoresceína para determinar H2O2 em amostras de águas naturais (LD = 2 nmol L-1 e LQ = 7 nmol L-1). Enquanto outros métodos demandam a análise imediata da amostra, neste caso, o fluoróforo permanece estável por cerca de 48 h, facilitando as análises e o trabalho de campo. A concentração de H2O2 na água de chuva de Ribeirão Preto coletada de 2014 a 2017 variou entre 5,8 e 96 mol L1, com média ponderada pelo volume (MPV) de 28,9 ± 1,3 µmol L-1 (n = 88). Foi observado que a radiação solar foi um parâmetro mais importante na formação de H2O2 do que no seu consumo. Enquanto as concentrações MPV de sulfato (pH < 5) e nitrato na água de chuva decresceram em torno de 35% em 2017 com relação a 2014, as concentrações de H2O2 praticamente dobraram no mesmo período. A correlação negativa entre essas espécies evidencia que as políticas nacionais destinadas a reduzir as emissões veiculares podem alterar a capacidade oxidativa da atmosfera. As concentrações de H2O2, etanol e acetaldeído na fase gasosa em Ribeirão Preto (RP) e São Paulo (SP) foram determinadas, utilizando de forma pioneira no Brasil, o método de coleta do condensado. As concentrações de etanol na atmosfera de RP (15,0 ± 6,6 ppbv, n = 19) e SP (22,0 ± 9,4 ppbv, n = 10) foram relativamente próximas, apesar da frota veicular de SP ser ~ 16 vezes maior. Essas concentrações de etanol são cerca de 21 vezes maiores que aquelas relatadas nos Estados Unidos devido ao elevado uso de etanol combustível no Brasil. As médias das concentrações de H2O2 e acetaldeído na atmosfera foram, respectivamente, de 2,10 ± 1,46 e 16,3 ± 6,0 ppbv em RP; e 1,29 ± 0,62 e 14,4 ± 5,4 ppbv em SP. A avalição diurna mostrou que enquanto a concentração de H2O2 aumentou com a radiação solar, a concentração de etanol diminuiu numa taxa próxima da produção de acetaldeído. Esses resultados indicam que o H2O2 pode ser um oxidante importante de etanol a acetaldeído em fase gasosa, sendo este último de elevada toxicidade para o ser humano. Os fluxos na interface ar-água nos locais estudados em RP e SP mostram que o corpo dágua funcionou como um sumidouro de H2O2. Já o fluxo de etanol foi variável, isto é, ora invasivo e ora evasivo, com evidências de uma importante produção fotoquímica dessa espécie no meio aquático. / The main objective of this work was to provide insights to better understand how the public policies focused on vehicular emissions, including the use of ethanol fuel, can affect the chemical composition of the atmosphere. Hydrogen peroxide (H2O2) is one of the most important oxidants in the troposphere and it can participate in reactions with a variety of organic and inorganic compounds. In this work, determination of H2O2, ethanol, acetaldehyde and other organic and inorganic species was carried out in the gas phase, rainwater and surface water. The fluorimetric method based on the formation of the 2, 7-dichlorofluorescein fluorophore was applied for the first time to determine H2O2 in natural water samples (LOD = 2 nmol L-1 and LOQ = 7 nmol L-1). While other methods require the immediate analysis of the sample, in this case, the fluorophore remains stable for about 48 h, facilitating the analyzes and fieldwork. H2O2 concentrations in rainwater of Ribeirão Preto collected between 2014 and 2017 ranged from 5.8 to 96 mol L-1, with a volume-weighted mean (VWM) of 28.9 ± 1.3 mol L-1 (n = 88). The solar radiation was observed to be a more important parameter in the formation of H2O2 than in its consumption. While the VWM concentrations of sulfate (pH <5) and nitrate in rainwater declined by approximately 35% in 2017 compared to 2014, H2O2 concentrations virtually doubled over the same period. The negative correlation between these species shows that national policies aimed at reducing vehicle emissions may modify the oxidizing capacity of the atmosphere. Gas phase H2O2, ethanol and acetaldehyde concentrations in Ribeirão Preto (RP) and São Paulo (SP) were determined using, for the first time in Brazil, the method of condensate collection. Ethanol concentrations in the atmosphere of RP (15.0 ± 6.6 ppbv, n = 19) and SP (22.0 ± 9.4 ppbv, n = 10) were relatively close, although the SP vehicle fleet is ~ 16 times higher. These ethanol concentrations are about 21 times higher than those reported in the United States due to the high use of ethanol fuel in Brazil. The mean concentrations of H2O2 and acetaldehyde in the atmosphere were, respectively, 2.10 ± 1.46 and 16.3 ± 6.0 ppbv in RP; and 1.29 ± 0.62 and 14.4 ± 5.4 ppbv in SP. Daytime variation showed that while H2O2 concentration increased with solar radiation, ethanol concentration decreased at a rate close to the one of acetaldehyde production. These results indicate that H2O2 may be an important oxidant of ethanol to acetaldehyde in the gas phase, the latter being highly toxic to humans. Fluxes in the air-water interface at the studied sites in RP and SP show that the water body worked as an H2O2 sink. On the other hand, ethanol fluxes were variable, i.e., sometimes invasive and sometimes evasive, with evidence of an important photochemical production of this species in the aquatic environment.

O parâmetro que determina o processo de transferência de oxigênio através da interface ar-água em escoamentos com superficie livre é o coeficiente de reaeração superficial, \'K IND.2\'. Existe um grande número de equações na literatura científica que realizam a previsão do coeficiente de reaeração, no entanto, a maioria dessas equações considera apenas algumas características hidráulicas do corpo de água como a velocidade e a profundidade, e ainda, como em sua maioria são de natureza empírica, acabam sendo adequadas para corpos de água específicos. Além destes dois parâmetros (velocidade e profundidade do escoamento), existem outros doze que são considerados importantes para estudos de reoxigenação em águas superficiais. É neste contexto que o objetivo deste trabalho foi estudar em condições de laboratório a influência da rugosidade do leito de um canal sobre o coeficiente de reaeração superficial. Além da rugosidade, foram variadas as condições de velocidade média do escoamento e profundidade da lâmina de água. A variação da rugosidade foi realizada através da implementação de obstáculos com geometria conhecida, dispostos transversalmente ao escoamento, e denominados como macro-rugosidades. Os resultados demonstraram evidências de que o coeficiente de reaeração superficial é controlado de forma significativa pela rugosidade do leito do canal. Foram desenvolvidos dois modelos matemáticos de natureza semi-empírica para a previsão do \'K IND.2\', os quais incorporam variáveis hidrodinâmicas e geométricas consideradas relevantes para o processo de transferência de massa na interface ar-água. / The parameter that determines the process of oxygen transfer through the air-water interface in flows with free surface is the superficial reaeration coefficient, \'K IND.2\'. There are a large quantity of equations in the cientific literature that perform the prevision of the reaeration coefficient; however, most of them consider only some of the hydraulic characteristics of water body; for example, the velocity and the depth. Most of these equations have empirical origin and are adequate just for a specific water body. In addition to these two parameters (velocity and depth of flow), there are another twelve important parameters in reoxygenation studies in superficial waters. In this context, the aim of this work was to study the influence of bed roughness of a channel on the superficial reaeration coefficient, under laboratory conditions. Besides the roughness, the conditions of mean velocity of the flow and depth of water were varied. The variation of roughness was done with implementation of obstacles with known geometry, arranged transversely to the flow direction, and called macro-roughness. The results have shown evidences that the surface reaeration coefficient is controlled significantly by the roughness of the channel bed. Two mathematical models of semi-empirical origin for the \'K IND.2\' prevision were developed, which incorporate hydrodynamic and geometric variables considered relevant in the process of mass transfer in air-water interface.

Considérant une particule isolée, la différence principale entre un colloïde actif et un colloïde passif réside dans le temps de persistance du régime balistique. La transition du régime balistique vers le régime diffusif est déterminée dans les deux cas par des coefficients de friction ou de manière équivalente par des coefficients de diffusion. Le mouvement d’une particule colloïdale passive micrométrique est diffusif lorsqu’il est observé sur des intervalles de temps d’au moins une microseconde, suffisamment longs pour que la direction de la quantité de mouvement soit rendue aléatoire par des collisions avec les molécules de solvant. A l’échelle macroscopique ces collisions se traduisent par un coefficient de friction de translation. Pour une particule colloïdale active, un mouvement diffusif est observé pour des intervalles de temps de plusieurs secondes, suffisamment longs pour que la direction d’auto-propulsion soit rendue aléatoire par la diffusion rotationnelle de la particule.Dans cette thèse, nous étudions le mouvement d’une particule colloïdale active déposée à la surface de l’eau. Des particules Janus aux propriétés catalytiques ont été préparées par dépôt de platine métal à la surface de particules de silice. La profondeur d’immersion des particules ainsi que leur orientation par rapport à la surface de l’eau ont été caractérisées et discutées en tenant compte des propriétés de mouillage non-uniformes de la surface des particules Janus. Le mouvement de particules isolées en présence de quantités variables d’eau oxygénée utilisée comme source d’énergie, a été enregistré par vidéo-microscopie optique et les trajectoires analysées en termes de déplacement carré moyen et de fonction d’auto-corrélation des vitesses. L’observation de deux types de trajectoires, rectilignes et circulaires, révèle la force effective ainsi que le couple induit par la décomposition catalytique de l’eau oxygénée à la surface de la particule Janus. Le résultat principal de ce travail est que le mouvement des particules actives confinées à l’interface persiste plus longtemps dans le régime balistique que celui de particules actives totalement immergées en solution. Ceci est dû au confinement qui réduit le nombre de degrés de liberté de rotation mais aussi aux conditions de mouillage partiel qui font apparaître des contributions supplémentaires à la friction de rotation. / At the single-particle level, the main difference between active colloids and passive ones is the time scale over which the motion crosses over from ballistic to diffusive regime. In both cases, friction coefficients or equivalently diffusion coefficients determine this time scale. For instance, the motion of a passive colloid of 1m radius is diffusive when observed over lag times longer than a microsecond, once the direction of its momentum has been randomized by collisions with solvent molecules. At the macroscopic scale these collisions are accounted for by the translational friction coefficient. For an active colloid the effective diffusive behavior observed over lag times larger than few seconds results from the randomization of the direction of self-propulsion by rotational diffusion. In this thesis we investigated the motion of an active Janus colloid trapped at air-water interface. Spherical catalytic Janus colloids have been prepared through the deposition of platinum metal at the surface of silica particles. Immersion depth of the Janus colloid as well as their orientation with respect to the water surface, has been characterized and interpreted in terms of the non-uniform wetting properties of the Janus particles. The motion of the active Janus colloids in the presence of various concentration of hydrogen peroxide H2O2 as fuel was characterized by video microscopy and the trajectories analyzed through the mean square displacement and the velocity autocorrelation function. The types of trajectories, directional and circular ones that we observed in our experiments, revealed the effective force and torque induced by the catalytic decomposition of H2O2. At the water surface, active colloids perform more persistent directional motions as compared to the motions performed in the bulk. This has been interpreted as due to the loss of degrees of freedom resulting from the confinement at interface and also to the partial wetting conditions that possibly bring new contributions to the rotational friction at interface.

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