Diffusion-driven growth and dissolution of quasi-static bubbles

Mención Internacional en el título de doctorTesis por compendio de publicacionesGrowing or dissolving bubbles are present in countless mass transfer processes that involve liquid and gas phases. This thesis comprises the fundamental study of four distinct but closely related problems concerning the diffusion-driven dissolution and growth of quasi-static gas bubbles. The term ‘quasi-static’ loosely describes the condition under which advection effects contribute poorly to the the rate of growth or dissolution of the bubble; ‘diffusion-driven’ indicates that mass transfer is governed by the solute diffusion in the surrounding bulk liquid. In super- or under-saturated solutions, diffusion effects are critical in the growth or dissolution behaviour of bubbles adhered to substrates including gas-evolving electrodes, and of bubbles in viscoelastic gels or under confinement, to name but a few examples. We first explore the dissolution of mm-sized CO2 spherical cap bubbles immersed in air-saturated water and adhered to collagen-coated glass and PMMA substrates. We validate a theoretical and numerical model against our experiments. Both account for the relevant influence of the contact angle dynamics and presence of the substrate on mass transfer across the bubble interface. We then focus on the study of the so-called ‘history effect’, namely the contribution of any past mass transfer events between a gas bubble and its liquid surroundings towards the current bubble growth or dissolution rate. The history effect arises when the concentration of dissolved gas at the bubble surface, dictated by Henry’s law, depends on time. Firstly, we provide a theoretical treatment of the history effect under the assumptions of spherical symmetry and negligible advection. Secondly, we perform experiments on isolated spherical CO2 bubbles adhered to a flat plate in carbonated water. This configuration was chosen for being closer to several practical applications. Additionally, we perform simulations to quantify the importance of the history effect versus the effects of boundary-induced advection and density-induced natural convection on the bubble dynamics. The third scenario entails the dissolution of a cylindrical CO2 bubble confined in a horizontal Hele-Shaw cell dissolving in air-saturated water. We visualize and track, by means of planar laser-induced fluorescence, the boundary layer of dissolved CO2 that propagates by diffusion from the dissolving bubble. The diffusion-driven transport of CO2 are then described by two simple analytical diffusion models which are then validated against numerical simulations. Finally, the fluorescence intensity profiles are related to the expected CO2 concentration and pH profiles. The fourth and final study is centered on the growth dynamics of a succession of H2 bubbles under constant-current electrolysis. The bubbles nucleate and grow on a micropillar protruding from an otherwise flat silicon electrode. The accumulation of dissolved H2 near the gas-evolving electrode is hindered by several depletion sources, including depletion from previous bubbles in the succession. The degree of supersaturation near the electrode, and consequently the bubble growth rates, are found to be largely unsteady and prone to fluctuations. Moreover, depletion effects (e.g. from parasitic bubbles growing nearby) are responsible for a notable retardation in the growth rate as the bubbles approached their departure size.Incontables procesos de transferencia de masa entre fases líquidas y gaseosas cuentan con la presencia de burbujas que crecen o se disuelven. Esta tesis engloba el estudio fundamental de cuatro problemas distintos sobre el crecimiento o la disolución por difusión de burbujas cuasi-estáticas. El término “cuasi-estático” describe de manera genérica la condición bajo la cual los efectos convectivos contribuyen de forma escasa al ritmo de crecimiento o disolución de la burbuja; “por difusión” indica que la transferencia de masa está siendo gobernada por la difusión del gas disuelto en el líquido que rodea la burbuja. En disoluciones sobreo sub-saturadas, los efectos difusivos son críticos en el comportamiento de crecimiento o disolución de burbujas adheridas a sustratos incluyendo electrodos que evolucionan gas, y de burbujas en geles viscoelásticos o en confinamiento, por ejemplo. Primero exploramos la disolución de burbujas de CO2 con forma de casquete esférico (de tamaño milimétrico) inmersas en agua saturada de aire y adheridas a placas de cristal o PMMA. Validamos un modelo teórico y numérico contra nuestros experimentos. Ambos tienen en cuenta el efecto influyente de la dinámica de la línea de contacto y la presencia de la placa en la transferencia de masa a través de la interfaz de la burbuja. Después nos centramos en el estudio del llamado ‘efecto de historia’, concretamente la contribución que los eventos pasados de transferencia de masa entre el líquido y la burbuja tienen en el ritmo actual de crecimiento o disolución de la burbuja. El efecto de historia surge cuando la concentración del gas soluto en la superficie de la burbuja, dictada por la ley de Henry, depende en el tiempo. En primer lugar presentamos un tratamiento teórico del efecto de historia bajo las hipótesis de simetría esférica y advección despreciable. En segundo lugar, realizamos experimentos en burbujas esféricas de CO2 adheridas a una placa plana en agua carbonatada. Adicionalmente, hacemos simulaciones para cuantificar el efecto de historia en la dinámica de las burbujas junto a los efectos de la advección inducida por la superficie no estacionaria de la burbuja y por convección natural. El tercer escenario consiste en la disolución de una burbuja cilíndrica de CO2 confinada en una celda Hele-Shaw horizontal en agua saturada de aire. Visualizamos y registramos, mediante fluorescencia inducida por láser, la capa límite de CO2 disuelto que se propaga por difusión desde la burbuja. Seguidamente, describimos el transporte por difusión de CO2 mediante dos sencillos modelos analíticos que son posteriormente validados frente a simulaciones numéricas. Finalmente, mostramos la relación del perfil de intensidad de fluorescencia con los perfiles de concentración de CO2 y de pH calculados. El cuarto y último estudio se centra en la dinámica de crecimiento de una sucesión de burbujas de H2 producidas mediante electrólisis a intensidad de corriente eléctrica constante. Las burbujas nuclean y crecen en un micro-pilar fabricado sobre un electrodo de silicio plano. La acumulación del hidrógeno disuelto cerca del electrodo es ralentizada por varias fuentes de pérdida de gas, en las que se incluye las pérdidas inducidas por las propias burbujas. El grado de sobresaturación cerca del electrodo, y consecuentemente el ritmo de crecimiento de las burbujas, son altamente inconstantes y propensos a fluctuar. Además, las pérdidas (debido, por ejemplo, a la formación cercana de burbujas parasíticas) son responsables de un notable enlentecimiento en el ritmo de crecimiento a medida que las burbujas van alcanzando el tamaño de desprendimiento.Programa Oficial de Doctorado en Mecánica de FluidosPresidente: Benoit Scheid.- Secretario: Daniel Fúster Salamero.- Vocal: Jesús Carlos Martínez Bazá

Dissolution of a CO2 spherical cap bubble adhered to a flat surface in air-saturated water

Bubbles adhered to partially hydrophobic flat surfaces often attain a spherical cap shape with a contact angle much greater than zero. We address the fundamental problem of the diffusion-driven dissolution of a sessile spherical cap bubble (SCB) adhered to a flat smooth surface. In particular, we perform experiments on the dissolution of CO2 bubbles (with initial radii similar to 1 mm) immersed in air-saturated water adhered to two substrates with different levels of hydrophobicity. It is found that the contact angle dynamics plays an important role in the bubble dissolution rate. A dissolution model for a multicomponent SCB in an isothermal and uniform pressure environment is then devised. The model is based on the quasi-stationary approximation. It includes the effect of the contact angle dynamics, whose behaviour is predicted by means of a simplified model based on the results obtained from adhesion hysteresis. The presence of an impermeable substrate hinders the overall rate of mass transfer. Two approaches are considered in its determination: (a) the inclusion of a diffusion boundary layer-plate interaction model and (b) a finite-difference solution. The model solutions are compared with the experimental results, yielding fairly good agreement.The authors gratefully acknowledge the support of Total E&P Recherche et Développement through study agreement FR00006995, and the Spanish Ministry of Economy and Competitiveness through grant DPI2014-59292-C3-1-P

Diffusion of dissolved CO2 in water propagating from a cylindrical bubble in a horizontal Hele-Shaw cell

The dissolution of a gas bubble in a confined geometry is a problem of interest in technological applications such as microfluidics or carbon sequestration, as well as in many natural flows of interest in geophysics. While the dissolution of spherical or sessile bubbles has received considerable attention in the literature, the case of a two-dimensional bubble in a Hele-Shaw cell, which constitutes perhaps the simplest possible confined configuration, has been comparatively less studied. Here, we use planar laser-induced fluorescence to experimentally investigate the diffusion-driven transport of dissolved CO2 that propagates from a cylindrical mm-sized bubble in air-saturated water confined in a horizontal Hele-Shawcell. We observe that the radial trajectory of an isoconcentration front, r(f) (t), evolves in time as approximately r(f) - R-0 alpha root t, where R-0 denotes the initial bubble radius. We then characterize the unsteady CO2 concentration field via two simple analytical models, which are then validated against a numerical simulation. The first model treats the bubble as an instantaneous line source of CO2, whereas the second assumes a constant interfacial concentration. Finally, we provide an analogous Epstein-Plesset equation with the intent of predicting the dissolution rate of a cylindrical bubble.We acknowledge the support of the Spanish Ministry of Economy and Competitiveness through Grants No. DPI2014-59292-C3-1-P and No. DPI2015-71901-REDT, partly funded through European Funds

The history effect in bubble growth and dissolution. Part 1. Theory

The term "history effect" refers to the contribution of any past mass transfer events between a gas bubble and its liquid surroundings towards the current diffusion-driven growth or dissolution dynamics of that same bubble. The history effect arises from the (non-instantaneous) development of the dissolved gas concentration boundary layer in the liquid in response to changes in the concentration at the bubble interface caused, for instance, by variations of the ambient pressure in time. Essentially, the history effect amounts to the acknowledgement that at any given time the mass flux across the bubble is conditioned by the preceding time history of the concentration at the bubble boundary. Considering the canonical problem of an isolated spherical bubble at rest, we show that the contribution of the history effect in the current interfacial concentration gradient is fully contained within a memory integral of the interface concentration. Retaining this integral term, we formulate a governing differential equation for the bubble dynamics, analogous to the well-known Epstein-Plesset solution. Our equation does not make use of the quasi-static radius approximation. An analytical solution is presented for the case of multiple step-like jumps in pressure. The nature and relevance of the history effect is then assessed through illustrative examples. Finally, we investigate the role of the history effect in rectified diffusion for a bubble that pulsates under harmonic pressure forcing in the non-inertial, isothermal regime.The authors acknowledge the support of the Spanish Ministry of Economy and Competitiveness through grant DPI2014-59292-C3-1-P, partly financed by European funds

Shaky life of a water drop in an anise oil-rich environment

This paper is associated with a video winner of a 2018 APS/DFD Milton van Dyke Award for work presented at the DFD Gallery of Fluid Motion. The original video is available online at the Gallery of Fluid Motion, https://doi.org/10.1103/APS.DFD.2018.GFM.V0054This paper is associated with a video winner of a 2018 APS/DFD Milton van Dyke Award for work presented at the DFD Gallery of Fluid Motion.We acknowledge the support of the Spanish FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación through Grants No. DPI2014-59292-C3-1-P, No. DPI2015-71901-REDT, and No. DPI2017-88201-C3-3-R

Role of Tetraspanins CD9 and CD151 in Primary Melanocyte Motility

Tetraspanins CD9 and CD151 have been implicated in cellular motility and intercellular adhesion in several cellular types. Here, we have studied the subcellular localization and the functional role of these molecules in primary melanocytes. We found that endogenous tetraspanins preferentially clustered in areas of melanocyte homotypic intercellular contacts and at the tips of dendrites. These observations were further confirmed using time-lapse fluorescence confocal microscopy of melanocytes transfected with CD9– and CD151–GFP (green fluorescent protein) constructs, suggesting an involvement of these proteins in cellular contacts and migration. Cell adhesion and migration assays performed using blocking monoclonal antibodies against CD9 and CD151 showed no significant effect on cell–extracellular matrix adhesion, whereas the migration of melanocytes was significantly enhanced. The regulation of the migratory capacity of melanocytes by CD9 and CD151 was further confirmed knocking down the endogenous expression of these tetraspanins with small interference RNA oligonucleotides. Therefore, tetraspanin molecules are localized at motile structures in primary human melanocytes regulating the migratory capacity of these cells

Gas bubble evolution on microstructured silicon substrates

The formation, growth and detachment of gas bubbles on electrodes are omnipresent in electrolysis and other gas-producing chemical processes. To better understand their role in the mass transfer efficiency, we perform experiments involving successive bubble nucleations from a predefined nucleation site which consists of a superhydrophobic pit on top of a micromachined pillar. The experiments on bubble nucleation at these spots permit the comparison of mass transfer phenomena connected to electrolytically generated H$_2$ bubbles with the better-understood evolution of CO$_2$ bubbles in pressure-controlled supersaturated solutions. In both cases, bubbles grow in a diffusion-dominated regime. For CO$_2$ bubbles, it is found that the growth rate coefficient of subsequent bubbles always decreases due to the effect of gas depletion. In contrast, during constant current electrolysis, the bubble growth rates are affected by the evolution of a boundary layer of dissolved H$_2$ gas near the flat electrode which competes with gas depletion. This competition results in three distinct regimes. Initially, the bubble growth slows down with each new bubble in the succession due to the dominant depletion of the newly-formed concentration boundary layer. In later stages, the growth rate increases due to a local increase of gas supersaturation caused by the continuous gas production and finally levels off to an approximate steady growth rate. The gas transport efficiency associated with the electrolytic bubble succession follows a similar trend in time. Finally, for both H$_2$ and CO$_2$ bubbles, detachment mostly occurs at smaller radii than theory predicts and at a surprisingly wide spread of sizes. A number of explanations are proposed, but the ultimate origin of the spreading of the results remains elusive

Solar-Simulated Ultraviolet Radiation Induces Abnormal Maturation and Defective Chemotaxis of Dendritic Cells

Exposure to ultraviolet (UV) light induces immunosuppression. Different evidences indicate that this phenomenon is mainly a consequence of the effect of UV light on skin dendritic cells (DC). To investigate the cellular and molecular basis of this type of immunosuppression, we assessed in vitro the effect of solar-simulated UV radiation on the phenotypic and functional characteristics of human monocyte-derived DC and Langerhans-like DC. UV radiation induced a decreased expression of molecules involved in antigen capture as DC-SIGN and the mannose receptor. This effect was accompanied by a diminished endocytic capacity, an enhanced expression of molecules involved in antigen presentation such as major histocompatibility complex-II and CD86, and a significant increase in their capability to stimulate T cells. Furthermore, irradiated DC failed to acquire a full mature phenotype upon treatment with lipopolysaccharide. On the other hand, solar-simulated radiation induced the secretion of tumor necrosis factor-αand interleukin (IL)-10 by DC, but no IL-12. Interestingly, solar-simulated UV radiation also caused an altered migratory phenotype, with an increased expression of CXCR4, and a lack of induction of CCR7, thus correlating with a high chemotactic response to stromal cell-derived factor 1(SDF-1) (CXCL12), but not to secondary lymphoid tissue chemokine (SLC) (CCL21). These data indicate that solar-simulated UV radiation induces a defective maturation and an anomalous migratory phenotype of DC

Novel SCN5A mutation associated with idiopathic ventricular fibrillation due to subclinical Brugada syndrome

Idiopathic ventricular fibrillation can be caused by subclinical channelopathies such as Brugada syndrome. Our objective is to study the clinical behaviour of a new SCN5A mutation found in a woman with idiopathic ventricular fibrillation. A 53-year-old woman presented with multiple episodes of ventricular fibrillation, a structurally normal heart and normal baseline electrocardiogram. Genetic testing included KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2 and KCNJ2 and identified a mutation in SCN5A (D1816fs/g98747-98748insT). We studied 15 immediate family members by means of electrocardiogram, echocardiogram, flecainide challenge test and genetic study. Eight subjects had the mutation. The flecainide challenge test was positive for Brugada syndrome in two subjects in the case group and none in the control group. The PR and QRS intervals on the baseline electrocardiogram were longer in the case group. The left atrial volume indexed to body surface was higher in the case group, likely due to the fact that two patients with the mutation had atrial fibrillation and none had it in the control group. The D1816fs/g98747-98748insT mutation in SCN5A may be associated with idiopathic ventricular fibrillation and Brugada syndrome with a broad phenotypic spectrum and incomplete penetrance. Genetic testing may be useful to identify the etiology of idiopathic ventricular fibrillation in patients with a negative thorough clinical evaluation

Emociones políticas y virtudes epidémicas en el siglo XVIII

El proyecto se propone abrir nuevas vías en la enseñanza de las Humanidades en la UCM mediante la práctica de una historia de las ideas del siglo XVIII que atiende a los condicionantes materiales de la cultura y a la valoración de las emociones como índices de construcción de imágenes de lo privado y lo público. El proyecto pretende, por un lado, explorar los mecanismos materiales de producción de ideas y creencias compartidas por la sociedad del siglo XVIII, teniendo en cuenta los diferentes contextos de la Ilustración Francesa, Alemana, Judía y Escocesa, con especial atención a la formación de metáforas políticas y a las emociones estéticamente más aceptadas y difundidas en la época analizada. La otra dimensión estudiada por el proyecto se refiere a los procesos de configuración de lo público y la crítica intelectual del poder, tomando como instrumento de análisis la comunicación de ideas materializada en la correspondencia, en la prensa, en los libros y en el proyecto de la Enciclopedia. Este programa de trabajo tendrá como principal destinatario el alumnado de Grado, Máster y Doctorado de la UCM, al que se invitará a las sesiones de trabajo del equipo, especialmente al matriculado en las asignaturas impartidas durante el curso 2016/17 por la IP. El proyecto reúne a destacados especialistas de la UCM y de otras universidades madrileñas y españolas, además de contar entre sus miembros con estudiantes de doctorado, que propiciarán la difusión de las actividades entre los estudiantes UCM, y con personal de administración y servicios, a los que se asignarán tareas relacionadas con la difusión y transferencia de los resultados del proyecto, a la sociedad, a la comunidad universitaria UCM y a los estudiantes Erasmus que reciba en el curso 2016/17 la Facultad de Filosofía de la UCM