Persona: Rodríguez Hakim, Mariana
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Rodríguez Hakim
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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 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.