Persona:
Rodríguez Hakim, Mariana

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ORCID
0000-0002-8239-2487
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Rodríguez Hakim
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Mariana
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2019 - 201912020 - 20211
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Autor: Shaqfeh, Eric S. G. ×

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Mostrando 1 - 2 de 2
  • Miniatura
    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, Mariana
    Evaporative 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.
  • Miniatura
    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, Mariana
    We 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.