Persona: Rodríguez Hakim, Mariana
Cargando...
Dirección de correo electrónico
ORCID
0000-0002-8239-2487
Fecha de nacimiento
Proyectos de investigación
Unidades organizativas
Puesto de trabajo
Apellidos
Rodríguez Hakim
Nombre de pila
Mariana
Nombre
6 resultados
Resultados de la búsqueda
Mostrando 1 - 6 de 6
Publicación Variations in human saliva viscoelasticity affect aerosolization propensity(Royal Society of Chemistry, 2022-01-26) Räz, Linard; Vermant, Jan; Rodríguez Hakim, MarianaSome contagious diseases, such as COVID-19, spread through the transmission of aerosols and droplets. Aerosol and droplet formation occurs inside and outside of the respiratory tract, the latter being observed during speaking and sneezing. Upon sneezing, saliva is expelled as a flat sheet, which destabilizes into filaments that subsequently break up into droplets. The presence of macromolecules (such as mucins) in saliva influences the dynamics of aerosol generation, since elasticity is expected to stabilize both fluid sheets and filaments, hence deterring droplet formation. In this study, the process of aerosol formation outside the respiratory tract is systematically replicated using an impinging jet setup, where two liquid jets collide and form a thin fluid sheet that can fragment into ligaments and droplets. The experimental setup enables us to investigate a range of dynamic conditions, quantified by the relevant non-dimensional numbers, which encompass those experienced during sneezing. Experiments are conducted with human saliva provided by different donors, revealing significant variations in their stability and breakup. We quantify the effect of viscoelasticity via shear and extensional rheology experiments, concluding that the extensional relaxation time is the most adequate measure of a saliva's elasticity. We summarize our results in terms of the dimensionless Weber, Reynolds, and Deborah numbers and construct universal state diagrams that directly compare our data to human sneezing, concluding that the aerosolization propensity is correlated with diminished saliva elasticities, higher emission velocities, and larger ejecta volumes. This could entail variations in disease transmission between individuals which hitherto have not been recognized.Publicación Instability and symmetry breaking in binary evaporating thin films over a solid spherical dome(Cambridge University Press, 2021-05-25) Shi, Xingyi; Shaqfeh, Eric S. G.; Fuller, Gerald G.; Rodríguez Hakim, MarianaWe examine the axisymmetric and non-axisymmetric flows of thin fluid films over a spherical glass dome. A thin film is formed by raising a submerged dome through a silicone oil mixture composed of a volatile, low surface tension species (1 cSt, solvent) and a non-volatile species at a higher surface tension (5 cSt, initial solute volume fraction ϕ0). Evaporation of the 1 cSt silicone oil establishes a concentration gradient and, thus, a surface tension gradient that drives a Marangoni flow that leads to the formation of an initially axisymmetric mound. Experimentally, when ϕ0⩽0.3%, the mound grows axisymmetrically for long times (Rodríguez-Hakim et al., Phys. Rev. Fluids, vol. 4, 2019, pp. 1–22), whereas when ϕ0⩾0.35%, the mound discharges in a preferred direction, thereby breaking symmetry. Using lubrication theory and numerical solutions, we demonstrate that, under the right conditions, external disturbances can cause an imbalance between the Marangoni flow and the capillary flow, leading to symmetry breaking. In both experiments and simulations, we observe that (i) the apparent, most amplified disturbance has an azimuthal wavenumber of unity, and (ii) an enhanced Marangoni driving force (larger ϕ0)leads to an earlier onset of the instability. The linear stability analysis shows that capillarity and diffusion stabilize the system, while Marangoni driving forces contribute to the growth in the disturbances.Publicación Effects of bulk elasticity on sheet formation and expansion(Elsevier, 2022-10-01) Stricker, Laura; Vermant, Jan; Rodríguez Hakim, MarianaThe destabilization, fragmentation, and atomization of thin fluid sheets governs processes such as the aerosolization of sneeze ejecta, agrochemical spraying, and fuel injection in liquid rocket engines. Although the evolution, stability, and breakup of fluid sheets composed of a Newtonian liquid has been extensively studied, the morphology and dynamics of viscoelastic fluid sheets remains poorly understood. This manuscript provides a theoretical and numerical framework that integrates the effects of fluid elasticity, surface tension, inertia, and viscosity to predict the morphology, velocity, and stress within stable fluid sheets composed of viscoelastic fluids as a function of the dimensionless Weber, Reynolds, and Weissenberg numbers. We find a non-monotonic behavior in the sheet’s size, velocity, and stress distribution as a function of the ratio between the Weissenberg and the Weber numbers. In particular, a minimum in the sheet’s size and a maximum in the stress occur when such a ratio is of the order of unity. We interpret these results as the consequence of the competing effects of the growth-favoring inertia and the restoring elastic forces acting within the sheet.Publicación Single bubble and drop techniques for characterizing foams and emulsions(Elsevier, 2020-12-01) Chandran Suja, V.; Fuller, G. G.; Rodríguez Hakim, Mariana; Tajuelo Rodríguez, JavierThe physics of foams and emulsions has traditionally been studied using bulk foam/emulsion tests and single film platforms such as the Scheludko cell. Recently there has been a renewed interest in a third class of techniques that we term as single bubble/drop tests, which employ isolated whole bubbles and drops to probe the characteristics of foams and emulsions. Single bubble and drop techniques provide a convenient framework for investigating a number of important characteristics of foams and emulsions, including the rheology, stabilization mechanisms, and rupture dynamics. In this review we provide a comprehensive discussion of the various single bubble/drop platforms and the associated experimental measurement protocols including the construction of coalescence time distributions, visualization of the thin film profiles and characterization of the interfacial rheological properties. Subsequently, we summarize the recent developments in foam and emulsion science with a focus on the results obtained through single bubble/drop techniques. We conclude the review by presenting important venues for future research.Publicación Evaporation-driven solutocapillary flow of thin liquid films over curved substrates(American Physical Society, 2019-03-13) Barakat, Joséph M.; Shi, Xingyi; Shaqfeh, Eric S. G.; Fuller, Gerald G.; Rodríguez Hakim, MarianaEvaporative loss of a volatile solvent can induce concentration inhomogeneities that give rise to spatial gradients in surface tension and subsequent solutocapillary Marangoni flows. This phenomenon is studied in the context of ultrathin liquid films resting atop curved convex substrates in contact with a fluid reservoir. Experiments are conducted with low-molecular-weight polydimethylsiloxane (silicone oil) mixtures composed of a volatile solvent and trace amounts of a nonvolatile solute. A theoretical model based on the thin-film approximation is developed, incorporating the effects of evaporative mass loss, gravity, capillarity, van der Waals forces, species diffusion, and Marangoni stresses. The spatiotemporal evolution of this system is studied by modulating the rate of evaporation of the volatile species and the bulk solute volume fraction in the mixture. The experiments and accompanying numerical simulations reveal that both Marangoni stresses and stabilizing van der Waals interactions between the substrate and the free surface can induce flow reversal and film regeneration. Their relative contribution is modulated by the solutocapillary Marangoni number, which is proportional to the bulk concentration of nonvolatile species in the mixture. Furthermore, it is revealed that increasing the rate of evaporation enhances the volumetric flow rate from thicker, solvent-rich areas towards thinner, solute-rich regions of the film. Although quantitative differences between the theory and the experiments are observed within certain ranges of the controlled parameters, the model qualitatively reproduces the flow regimes observed in the experiments and elucidates the complex interplay among the various physical forces.Publicación Asphaltene-induced spontaneous emulsification: Effects of interfacial co-adsorption and viscoelasticity(American Institute of Physics, 2020-07-01) Anand, Satyam; Yao, Zhen; Kannan, Aadithya; Fuller, Gerald G.; Rodríguez Hakim, Mariana; Tajuelo Rodríguez, JavierAsphaltenes are a class of high molecular weight aromatic compounds found in crude oil. They adsorb onto toluene-water interfaces and induce a spontaneous emulsification phenomenon, whereby stable water-in-oil emulsions form without the need of an external energy input. This work aims to control and understand the factors affecting spontaneous droplet formation in the presence of asphaltene adsorption. This is particularly useful for crude oil refining, where the presence of a stable emulsion hampers the efficiency of downstream processing operations. We explore the effect of the addition of copolymers designed as crude oil flow improvers as a means to control the extent of emulsion formation. We find that the polymers competitively adsorb onto the toluene-water interface and diminish spontaneous emulsification. We also conduct fluorescence microscopy experiments and measurements of the interfacial energy to determine the mechanism of spontaneous emulsification in asphaltene systems. We conclude that an emulsion forms via the diffusion of molecular water into the oil phase and subsequent binding with asphaltene aggregates, leading to the nucleation of micrometer-sized water droplets. We find that the polymer forms complexes with the dissolved asphaltenes, possibly hampering the ability of diffused water to bind to the asphaltenes and reducing the extent of spontaneous emulsification. Finally, we investigate the role of interfacial shear and dilatational viscoelasticity to better understand which fundamental interfacial properties are important in the emulsification of asphaltene-laden systems. We find that the rate of formation of an interfacial microstructural network is inversely correlated with the extent and rate of spontaneous emulsification.