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Theses

Ecoulement de gouttes couvertes dans une contraction

Abstract : The flow of oil drops in water through a constricted channel is of interest for many applications such as oil extraction or microfluidics. In the literature, the condition of pore clogging under a pressure gradient has been extensively studied for drops and bubbles. The relation between flowrate and pressure involves the difference in Laplace pressures at the front and back of the drop, and thus the interfacial tensions at the front and the back. The presence of species adsorbed on the surface lowering the interfacial tension, such as surfactants or colloidal particles, therefore modifies not only the clogging threshold but also the value of the flowrate above this threshold. The objective of this thesis is to study the flow, under an imposed pressure gradient, of drops whose surface is initially saturated with surfactants (above the CMC) or with particles, through cylindrical constricted capillaries. We show how measurements of flowrate by image analysis can provide measurements of the interfacial tensions. In the case of surfactant-laden drops, we measure an increase in the interfacial tension at the front which results from a competition between the surface expansion effects and the transport by a Marangoni effect. In the case of particle-laden drops, we show that both the velocity of the drop and the radius of the particles adsorbed on its surface control the flow regime. At low velocities, the wetting of oil on the capillary walls is observed at the front of the drop; at larger velocities, the flow depends on the particle size compared to the thickness of the lubricating film, according to this criterion either the occurence of friction of the particles on the channel walls or a viscous lubrication regime are observed. These regimes are responsible for a greater or lesser accumulation of particles at the back of the drop, decreasing the back interfacial tension and giving rise to various mechanisms of interface destabilization. For both systems, we show that the presence of adsorbed species has little effect on the clogging condition. Nevertheless, we measure an increase in the passage time of the drops covered with surfactants or particles, which results from the coupling of interfacial dynamics and flow through the contraction.
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  • HAL Id : tel-03550783, version 1

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Franz de Soete. Ecoulement de gouttes couvertes dans une contraction. Physique [physics]. Université Paris sciences et lettres, 2021. Français. ⟨NNT : 2021UPSLS082⟩. ⟨tel-03550783⟩

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