Using the classical molecular dynamics simulations, the interfacial partitioning of selected aromatic species, namely benzoic acid and neutral and zwitterionic form of L-phenylalanine, was studied in the three slab systems: a) aqueous organics solution, b) palmitic acid monolayer in tilted condensed phase at aqueous organics solution and c) palmitic acid monolayer in tilted condensed - 2D gas phase coexistence at aqueous organics solution. The surface activity and the tendency to aggregate in particular at the air- aqueous and palmitic acid-aqueous interface was confirmed for all of the investigated aromatic species. The results of the simulation performed for the system of palmitic acid monolayer at benzoic acid solution were compared with the literature results of a similar simulation that employed a different parametrization. The comparison showed that the behaviour of the aromatic species at the fatty acid monolayer-aqueous interface strongly depends on the force field. The structural properties of the palmitic acid Langmuir monolayers were evaluated by means of the chain tilt angle and the headgroup region dihedral angle distributions analysis depending on the surface film density and the adsorbed aromatic species. The simulations mimicking the isothermal compression of the mixed monolayer in the...

Recent reports on the formation of hydrogen peroxide (H$_2$O$_2$) in water microdroplets produced via capillary condensation or pneumatic spraying have garnered significant attention. How covalent bonds in water could break under such conditions challenges our textbook understanding of physical chemistry and the water substance. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air-water interface are responsible for this chemical transformation. This thesis documents the findings of our exploration of this mystery via a comprehensive experimental investigation of H$_2$O$_2$ formation in (i) water microdroplets condensed on hydrophobic and hydrophilic substrates formed via hot water in the 50–70 ℃ range or ultrasonic humidifier under controlled air composition, and (ii) water microdroplets sprayed over a range of liquid flow-rates, the (shearing) air flow rates, and the air composition. Our glovebox experiments, with controlled gas composition, revealed that no H$_2$O$_2$(aq) was produced in water microdroplets condensed via heating water (detection limit ≥ 0.25 μM), regardless of the droplet size or the substrate wettability. In contrast, water droplets condensed via ultrasonic humidification contained significantly higher (~1 μM) H$_2$O$_2$ concentration. We pinpointed that ultrasonic humidifiers induced cavitation of tiny bubbles in water, which is known to form H$_2$O$_2$(aq) and other reactive species. Next, in the case of sprayed water microdroplets, also, we did not detect H$_2$O$_2$(aq) unless O$_3$(g) was present in the ambient atmosphere. In contrast, water microdroplets (sprayed or condensed) exposed to O$_3$(g) concentration in the range 2–5000 ppb formed 2–100 μM H$_2$O$_2$(aq); increasing the gas–liquid surface area, mixing, and contact duration enhanced the H$_2$O$_2$(aq) concentration. Therefore, we submit that the original reports suffered from experimental artifacts due to the high regional O$_3$(g) giving rise to H$_2$O$_2$(aq), and the air–water interface does not spontaneously produce H$_2$O$_2$(aq). The water surface merely facilitates the O$_3$(g) mass transfer, which then undergoes chemical transformations in the water to form H$_2$O$_2$(aq). Taken together, these findings offer an alternative explanation to the mysterious production of H$_2$O$_2$ in water microdroplets; These findings should also advance our understanding of the implications of this chemistry in natural and applied contexts.

No description available.

Yes / Understanding the dynamic free surface of geophysical flows has the potential to enable direct inference of the flow properties based on measurements of the free surface. An important step is to understand the inherent response of free surfaces in depth-limited flows. Here a model is presented to demonstrate that free surface oscillatory spatial correlation patterns result from individual surface features oscillating vertically as they advect over space and time. Comparison with laboratory observations shows that these oscillating surface features can be unambiguously explained by simple harmonic motion, whereby the oscillation frequency is controlled by the root-mean-square water surface fluctuation, and to a lesser extent the surface tension. This demonstrates that the observed “complex” wave pattern can be simply described as an ensemble of spatially and temporally distributed oscillons. Similarities between the oscillon frequency and estimated frequency of near-bed bursting events suggest that oscillon behaviour is linked with the creation of coherent flow structures.

Tesis por compendio / [ES] El análisis de los fenómenos transitorios durante las operaciones de llenado en conducciones de agua ha sido estudiado de manera detallada comparado con las maniobras de vaciado. En este último se encontró que no existen modelos matemáticos capaces de predecir el fenómeno. Esta investigación inicia estudiando el fenómeno transitorio generado durante el vaciado en una tubería simple, como paso previo para entender el comportamiento de las variables hidráulicas y termodinámicas durante el vaciado de agua en conducciones presurizadas de perfil irregular. Los análisis son realizados considerando dos situaciones: (i) la situación No. 1 corresponde al caso donde no hay válvulas de aire instaladas o cuando éstas han fallado por problemas operacionales o de mantenimiento, que representa la condición más desfavorable con respecto a la depresión máxima alcanzada; y (ii) la situación No. 2 corresponde al caso en donde se han instalado válvulas de aire en los puntos más elevados de la conducción para dar fiabilidad mediante el aire introducido al sistema previniendo de esta manera la depresión máxima. En esta tesis doctoral se ha desarrollado un modelo matemático para predecir el comportamiento de las operaciones de vaciado. El modelo matemático es propuesto para las dos situaciones mencionadas anteriormente. La fase líquida (agua) es simulada con un modelo de columna rígida, en el cual se desprecia la elasticidad del agua y de la tubería debido a que la elasticidad del aire es mucho mayor que estas; y la interfaz aire-agua es modelada con un modelo de flujo pistón, el cual asume que la columna de agua es perpendicular a la dirección principal del flujo. La fase de aire es modelada usando tres ecuaciones: (a) un modelo politrópico basado en el comportamiento energético, que considera la expansión de las bolsas de aire; (b) la formulación de las válvulas de aire para cuantificar la magnitud del caudal de aire admitido; y (c) la ecuación de continuidad de la bolsa de aire. Un sistema ordinario de ecuaciones diferenciales es solucionado utilizando la herramienta de Simulink de Matlab. El modelo matemático es validado empleando bancos experimentales localizados en los laboratorios de hidráulica de la Universitat Politècnica de València (Valencia, España) y en el Instituto Superior Técnico de la Universidad de Lisboa (Lisboa, Portugal). Los resultados muestran que el modelo matemático predice adecuadamente los datos experimentales de las presiones de las bolsas de aire, las velocidades del agua y las longitudes de las columnas de agua. Finalmente, el modelo matemático es aplicado a un caso de estudio para mostrar su aplicabilidad a situaciones prácticas, con el fin de poder ser empleado por ingenieros para estudiar el fenómeno en conducciones reales y así tomar decisiones acerca de la planificación de esta operación. / [CA] L'anàlisi dels fenòmens transitoris durant les operacions d'ompliment en conduccions d'aigua ha sigut estudiat de manera detallada comparat amb les maniobres de buidatge. En este últim es va trobar que no hi ha models matemàtics capaços de predir el fenomen. Esta investigació inicia estudiant el fenomen transitori generat durant el buidatge en una canonada simple, com a pas previ per a entendre el comportament de les variables hidràuliques i termodinàmiques durant el buidatge d'aigua en conduccions pressuritzades de perfil irregular. Les anàlisis són realitzats considerant dos situacions: (i) la situació No. 1 correspon al cas on no hi ha vàlvules d'aire instal·lades o quan estes han fallat per problemes operacionals o de manteniment, que representa la condició més desfavorable respecte a la depressió màxima aconseguida; i (ii) la situació No. 2 correspon al cas on s'han instal·lat vàlvules d'aire en els punts més elevats de la conducció per a donar fiabilitat per mitjà de l'aire introduït al sistema prevenint d'esta manera la depressió màxima. En esta tesi doctoral s'ha desenrotllat un model matemàtic per a predir el comportament de les operacions de buidatge. El model matemàtic és proposat per a les dos situacions mencionades anteriorment. La fase líquida (aigua) és simulada amb un model de columna rígida, en el qual es desprecia l'elasticitat de l'aigua i de la canonada pel fet que l'elasticitat de l'aire és molt major que estes; i la interfície aire-aigua és modelada amb un model de flux pistó, el qual assumix que la columna d'aigua és perpendicular a la direcció principal del flux. La fase d'aire és modelada usant tres equacions: (a) un model politròpic basat en el comportament energètic, que considera l'expansió de les bosses d'aire; (b) la formulació de les vàlvules d'aire per a quantificar la magnitud del cabal d'aire admés; i (c) l'equació de continuïtat de la bossa d'aire. Un sistema ordinari d'equacions diferencials és solucionat utilitzant la ferramenta de Simulink de Matlab. El model matemàtic és validat emprant bancs experimentals localitzats en els laboratoris d'hidràulica de la Universitat Politècnica de València (València, Espanya) i en l'Institut Superior Tècnic de la Universitat de Lisboa (Lisboa, Portugal). Els resultats mostren que el model matemàtic prediu adequadament les dades experimentals de les pressions de les bosses d'aire, les velocitats de l'aigua i les longituds de les columnes d'aigua. Finalment, el model matemàtic és aplicat a un cas d'estudi per a mostrar la seua aplicabilitat a situacions pràctiques, a fi de poder ser empleat per enginyers per a estudiar el fenomen en conduccions reals i així prendre decisions sobre la planificació d'esta operació. / [EN] The analysis of transient phenomena during water filling operations in pipelines of irregular profiles has been studied much more compared to emptying maneuvers. In the literature, there is a lack of knowledge about mathematical models of emptying operations. This research starts with the analysis of a transient phenomenon during emptying maneuvers in single pipelines, which is a previous stage to understand the emptying operation in pipelines of irregular profiles. Analysis are conducted under two typical situations: (i) one corresponding to either the situation where there are no air valves installed or when they have failed due to operational and maintenance problems which represents the worse condition due to causing the lowest troughs of subatmospheric pressure, and (ii) the other one corresponding to the situation where air valves have been installed at the highest point of hydraulic installations to give reliability by admitting air into the pipelines for preventing troughs of subatmospheric pressure. Particularly, this research developed a mathematical model to predict the behavior of the emptying operations. The mathematical model is proposed for the two aforementioned situations. The liquid phase (water) is simulated using a rigid water column model (RWCM), which neglects the pipe and water elasticity given that the elasticity of the entrapped air pockets is much higher than the one from the pipe and the water. The air-water interface is simulated with a piston flow model assuming that the water column is perpendicular with the main direction of the flow. Gas phase is modeled using three formulations: (a) a polytropic model based on its energetic behavior, which considers an expansion of air pockets; (b) an air valve characterization to quantify the magnitude of admitted air flow; and (c) a continuity equation of the air. An ordinary differential equations system is solved using the Simulink tool of Matlab. The proposed model has been validated using experimental facilities at the hydraulic laboratories of the Universitat Politècnica de València, Valencia, Spain, and the Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal. The results show how the mathematical model adequately predicts the experimental data, including the pressure oscillation patterns, the water velocities, and the lengths of the water columns. Finally, the mathematical model is applied to a case study to show a practical application, which can be used for engineers to study the phenomenon in real pipelines to make decisions about performing of the emptying operation. / Coronado Hernández, ÓE. (2019). Transient phenomena during the emptying process of water in pressurized pipelines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/120024 / Compendio

A superhydrophobic coating can be produced using a hydrophobic material textured with surface roughness on the micro-/nano-scale. Such a coating on the outside of a submersible body may result in reduced skin-friction drag due to a trapped layer of air in the coating. However, this layer may become unstable when subjected to elevated hydrostatic pressures, and a coating’s performance is compromised beyond a certain threshold (critical pressure). This thesis presents a numerical model for predicting the pressure tolerances of superhydrophobic coatings comprised of randomly deposited hydrophobic particles or fibers. We have also derived a set of force-balance-based analytical equations for predicting critical pressure in surfaces with ordered roughness, and compared our numerical model against it, observing reasonable agreement. The numerical model was then applied in a large parameter study, predicting critical pressure for coatings with a given set of microstructure properties.

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.

Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. <br><br> There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. <br><br> The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. <br><br> Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants. / Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen. <br><br> Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert. <br><br> Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.

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.