Persona: Rodríguez Hakim, Mariana
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Rodríguez Hakim
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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 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 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.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 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 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 How sighing regulates pulmonary surfactant structure and its role in breathing mechanics(American Association for the Advancement of Science (AAAS), 2025-09-24) Novaes Silva, Maria Clara; Rodríguez Hakim, Mariana; Thompson, Benjamin; Wagner, Norman; Hermans, Eline; Dupont, Lieven; Vermant, Jan; Ministerio de Ciencia, Innovación y Universidades, the European Social Fund Plus (FSE+)Pulmonary surfactants reduce the work of breathing, enhance compliance, and prevent alveolar collapse. Yet, their role extends beyond that of a simple surfactant; otherwise, exogenous surfactant therapy would fully restore compliance in acute respiratory distress syndrome (ARDS) by increasing surface concentration alone. Here, we show that interfacial microstructure and mechanics, regulated by spontaneous or ventilator-induced sighs, play a critical role. Using interfacial rheometry and structural analysis, including in situ neutron reflectometry and Raman-based techniques, we find that sighs enrich the air-liquid interface with saturated lipids, triggering structural rearrangements. This periodic “reset” transforms the layer into a mechanically robust, DPPC-rich film, where compressional hardening counteracts tension. These findings highlight the nonequilibrium dynamics of surfactant layers and underscore the importance of interfacial compressive stresses, not just tension, in governing lung mechanics. This mechanism helps sustain low interfacial stress and high compliance, offering mechanistic insight to guide protective ventilation strategies upon lung trauma and possibilities to optimize surfactant-enabled pulmonary treatment.Publicación Towards operating windows for pendant drop methods: tensiometry and rheometry of elastic interfaces(Springer, 2025-05-21) Rodríguez Hakim, Mariana; Jaensson, Nick; Vermant, Jan; Ministerio de Ciencia, Innovación y Universidades (MICIU), NextGenerationEUWe numerically evaluate the performance of two pendant drop techniques — Capillary Pressure Tensiometry (CPT) and Stress-Fitting Elastometry (SFE) — based on their ability to calculate the interfacial stress and dilatational rheological properties of complex interfaces. Although both methods incorporate simultaneous shape and pressure measurements, CPT assumes a spherical cap shape with isotropic deformations, allowing the interface to be fully characterized by a single scalar value for the surface stress. On the contrary, SFE accounts for mechanically resistant interfaces that exhibit non-uniform tensorial strain and stress fields. To compare these methods, we numerically generate drops with perfectly elastic (non-dissipative) interfaces and subject them to step-strain compressions of varying magnitudes. The calculations span a range of dimensionless parameters representing realistic drop volumes, geometries, and physical properties. We show that the local strain and/or stress vary along the surface, depending on the relative magnitude of the shear versus dilatational moduli. We analyze the strained interfaces using CPT and SFE, quantitatively evaluating their ability to predict the interfacial strains, stresses, and dilatational moduli. We then identify the configurations and analysis methods that yield the most accurate results. Finally, we assess the robustness of these methods by introducing random Gaussian noise to the interface profiles, with a magnitude comparable to experimental errors from image acquisition and processing. The performance of both methods is compared under both idealized and experimentally realistic (noisy) conditions.Publicación Facile and Robust Production of Ultrastable Micrometer-Sized Foams(ACS, 2023-05-23) Rodríguez Hakim, Mariana; Oblak, Luka; Vermant, JanStable foams that can resist disproportionation for extended periods of time have important applications in a wide range of technological and consumer materials. Yet, legislative initiatives limit the range of surface active materials that can be used for environmental impact reasons. There is a need for technologies to efficiently produce multiphase materials using more eco-friendly components, such as particles, and for which traditional thermodynamics-based processing routes are not necessarily efficient enough. This work describes an innovative foaming technology that can produce ultrastable Pickering-Ramsden foams, with bubbles of micrometer-sized dimensions, through pressure-induced particle densification. Specifically, aqueous nanosilica-stabilized foams are produced by foaming a suspension at subatmospheric pressures, allowing for adsorption of the particles onto large bubbles. This is followed by an increase back to atmospheric pressure, which induces bubble shrinkage and compresses the adsorbed particle interface, forming a strong elastoplastic network that provides mechanical resistance against disproportionation. The foam’s interfacial mechanical properties are quantified to predict the range of processing conditions needed to produce permanently stable foams, and a general stability criterion is derived by considering the interfacial rheological properties under slow, unidirectional compression. Foams that are stable against disproportionation are characterized by interfaces whose mechanical resistance to compressive deformations can withstand their tendency to minimize the interfacial stress by reducing their surface area. Our ultrastable nanosilica foams are tested in real-life applications by introducing them into concrete. In comparison to other commercial air entrainers, our microfoam improves concrete’s freeze–thaw resistance while supplying higher material strength, providing an economically attractive, industrially scalable, and durable alternative for use in real-life applications involving cementitious materials. The applicability of our stability criterion to other rheologically complex interfaces and the versatile nature of our foaming technology enables usage for a broad class of materials, beyond the construction industry.