Gala, Luigi Davide (2024) Characterization and Control of Interfacial Phenomena: Interface behavior of miscible systems and thin films in presence of complex flow conditions. [Tesi di dottorato]

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This dissertation delves into the intricate realm of interfacial phenomena, focusing on two distinct limit cases: miscible fluid dynamics and thin film drainage. Interfacial phenomena, occurring at the boundaries of different phases, present unique challenges due to the two-dimensional nature of interfaces, limiting sample sizes relative to bulk phases. The first part of the dissertation explores the ongoing debate on the existence of interfacial tension in miscible fluid systems, challenging traditional thermodynamic approaches. Miscible fluid interfaces, characterized by sharp gradients in concentration, temperature, density, or viscosity, hold significant importance in diverse fields such as geodynamics, polymer physics, and multiphase flow, with applications in oil recovery, hydrology, and filtration. The dissertation systematically investigates the interface behavior of a layered system comprising two miscible fluids subjected to sinusoidal rotational motion. A novel hydrodynamic instability, distinct from established phenomena, is identified, leading to the initiation of oscillatory Kelvin-Helmholtz instability and radial growth of fingers induced by centrifugal forces. This unprecedented destabilization scenario offers insights into potential applications, including controlled drop formation. In the context of thin film drainage, the second part of the dissertation emphasizes its crucial role in scientific and industrial processes. Thin film drainage influences coating, printing, stability of colloidal systems, lubrication, and various applications in nanotechnology and materials engineering. The study focuses on the interplay between thin film drainage and particle adsorption at the liquid/air interface. An unexplored consequence of particle adsorption is revealed, leading to a transition from immobility to mobility of the interface and an elevation in drainage velocity. This transition is attributed to the formation of a viscoelastic layer due to particle presence. The dissertation contributes to the understanding of interfacial phenomena in miscible fluid systems and thin film dynamics, addressing challenges and providing insights into potential applications. By manipulating parameters in the miscible fluid dynamics scenario, such as motion, viscosity ratio, diffusion, and interfacial tension, the dissertation demonstrates the tunability of finger characteristics. Additionally, in the thin film drainage context, the study identifies a novel effect of particle adsorption on interface mobility, opening avenues for further exploration in areas like protective coatings, biomedical applications, and nanotechnology. Overall, this dissertation highlights the significance of interfacial features across various length scales and their pivotal influence on diverse scientific and industrial phenomena.

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