Dissolution or growth of soluble spherical oscillating bubbles (original) (raw)
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Despite the prevalence of surface bubbles in many natural phenomena and engineering applications, the effect of surfactants on their surface residence time is not clear. Numerous experimental studies and theoretical models exist but a clear understanding of the film drainage phenomena is still lacking. In particular, theoretical works predicting the drainage rate of the thin film between a bubble and the free surface in the presence and absence of surfactants usually make use of the lubrication theory. On the other hand, in numerous natural situation and experimental works, the bubble approaches the free surface from a certain distance and forms a thin film at a later stage. This paper attempts to bridge these two approaches. In particular, in this paper, we review these works, and compare them to our Direct Numerical Simulations where we study the coupled influence of bubble deformation and surfactants on the rising and drainage process of a bubble beneath a free surface. In the present study, the level-set method is used to capture the air-liquid interfaces and the transport equation of surfactants is solved in an Eulerian framework. The axisymmetric simulations capture the bubble acceleration, deformation and rest (or drainage) phases from non-deformable to deformable bubbles, as measured by the Bond number (Bo), and from surfactant-free to surfactant coated bubbles, as measured by the Langmuir number (La). The results show that the distance h between the bubble and the free surface decays exponentially for surfactant-free interfaces (La = 0) and this decay is faster for non-deformable bubbles (Bo 1) than for deformable ones (Bo 1). The presence of surfactants (La > 0) slows down the decay of h, exponentially for large bubbles (Bo 1) and algebraically for small ones (Bo 1). For Bo ∼ 1, the lifetime is the longest and associated to (Marangoni) elasticity of the interfaces.
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The local and the terminal velocities, the size and the degree of bubbles' shape deformations were determined as a function of distance from the position of the bubble formation (capillary orifice) in solutions of n-octyltrimethylammonium bromide, n-octyldimethylphosphine oxide, n-octyl--d-glucopyranoside and n-octanoic acid.
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Langmuir : the ACS journal of surfaces and colloids, 2016
We investigate, both theoretically and experimentally, the role played by the oscillations of the cell membrane on the capture rate of substances freely diffusing around the cell. In order to obtain quantitative results, we propose and build up a reproducible and tunable biomimetic experimental model system to simulate the phenomenon of oscillation-enhanced (or depressed) capture rate (chemoreception) of a diffusant. The main advantage compared to real biological systems is, that the different oscillation parameters (type of deformation, frequencies and amplitudes) can be finely tuned. The model system we use is an anchored gas drop submitted to a diffusive flow of charged surfactants. When the surfactant meets the surface of the bubble, it is reversibly adsorbed. Bubble oscillations of the order of a few nanometers are selectively excited and surfactant transport is accurately measured The surfactant concentration past the oscillating bubbles was detected by conductivity measuremen...
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Surfactant transport dynamics and the consequences for rectified diffusion of microbubbles are treated for bubbles undergoing arbitrarily large-amplitude periodic radial oscillations. A perturbation technique is used to reveal averaged equations for the slow convection-enhanced diffusive transport of surfactant molecules. These equations have a readily obtained asymptotic limit in the form of a single nonlinear integral equationthis may be interpreted as a dynamic equilibrium adsorption isotherm. For a lightly populated interface, an explicit solution for the surface excess population of surfactants may be obtained. Bubble oscillations are shown to drive an increased number of surfactant molecules to the interface, if it is lightly populated, but to reduce the maximum possible population of surfactants on the interface. These effects have important consequences for rectified diffusion, in which the interfacial resistance to gas transfer of a surfactant monolayer is a strong function of the surface excess population.