Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G4: Bubbles: Surfactants and Foams |
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Chair: Emmanuelle Rio, Laboratoire de Physique des Solides Room: 3006 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G4.00001: Aging of clean foams Byung Mook Weon, Peter S. Stewart Aging is an inevitable process in living systems. Here we show how clean foams age with time through sequential coalescence events: in particular, foam aging resembles biological aging. We measure population dynamics of bubbles in clean foams through numerical simulations with a bubble network model. We demonstrate that death rates of individual bubbles increase exponentially with time, independent on initial conditions, which is consistent with the Gompertz mortality law as usually found in biological aging. This consistency suggests that clean foams as far-from-equilibrium dissipative systems are useful to explore biological aging. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G4.00002: The role of surface elasticity in liquid film formation Lorene Champougny, Benoit Scheid, Frederic Restagno, Emmanuelle Rio The formation of thin liquid films, either free standing (soap films) or deposited on a solid substrate (coated films), is of utmost importance for many applications, ranging from the control of foam stability to surface functionalization. In this work, the behavior of thin liquid films during their generation from a surfactant solution is investigated through comparison between a hydrodynamic model including surface elasticity and experiments. ``Twin'' models are proposed to describe the coating of films onto a solid plate (Landau-Levich-Derjaguin configuration) as well as soap film pulling (Frankel configuration) in a single framework. Experimental data are successfully fitted using the models, surface elasticity being the only adjustable parameter. For a given surfactant solution, the analyses of soap and coated films both yield the same value for the effective surface elasticity, showing that it is an intrinsic parameter of a surfactant solution. Conversely, we demonstrate that Frankel- or Landau-Levich-like experiments can be used in practice as surface rheometers to determine the numerical value of the (effective) surface elasticity of a solution, especially for values lower than those measurable by classical devices. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G4.00003: Rupture of vertical soap films Emmanuelle Rio Soap films are ephemeral and fragile objects. They tend to thin under gravity, which gives rise to the fascinating variations of colors at their interfaces but leads systematically to rupture. Even a child can create, manipulate and admire soap films and bubbles. Nevertheless, the reason why it suddenly bursts remains a mystery although the soap chosen to stabilize the film as well as the humidity of the air seem very important. One difficulty to study the rupture of vertical soap films is to control the initial solution. To avoid this problem we choose to study the rupture during the generation of the film at a controlled velocity. We have built an experiment, in which we measure the maximum length of the film together with its lifetime. The generation of the film is due to the presence of a gradient of surface concentration of surfactants at the liquid/air interface. This leads to a Marangoni force directed toward the top of the film. The film is expected to burst only when its weight is not balanced anymore by this force. We will show that this leads to the surprising result that the thicker films have shorter lifetimes than the thinner ones. It is thus the ability of the interface to sustain a surface concentration gradient of surfactants which controls its stability. [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G4.00004: Wall slip of foams close to the jamming transition S. Cohen-Addad, M. Le Merrer, R. Lespiat, R. Hohler Aqueous foams are dense packings of gas bubbles in a surfactant solution. They exhibit unique rheological properties [1]. When they flow along a solid smooth wall, they slip and experience viscous drag. This feature is crucial in many applications involving flow through microfluidic channels, pipes or spreading on surfaces. We focus on foams in the vicinity of the jamming transition where the bubbles are quasi spherical with small contact films at the wall and thick liquid channels between bubbles. What are the mechanisms of friction at play at the scale of the films, the channels and the bubbles that are at the origin of the macroscopic friction law? To address this question, we measure the velocity of a bubble monolayer or a wet 3D foam as it creeps along an immersed inclined plane, as a function of the inclination angle, bubble size and confinement. Two regimes of friction are evidenced: In addition to a previously reported non-linear Bretherton-like drag, we present the first direct evidence for a linear Stokes-like drag. We show that the key parameter governing the transition between the regimes is set by the Bond number for the monolayer or the confinement pressure for the foam. \\[4pt] [1] S. Cohen-Addad, R. Hohler, O. Pitois, Annu. Rev. Fluid Mech. (2013), \textbf{45}, 241. [Preview Abstract] |
(Author Not Attending)
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G4.00005: A numerical model to simulate foams during devolatilization of polymers Irfan Khan, Ravindra Dixit Customers often demand that the polymers sold in the market have low levels of volatile organic compounds (VOC). Some of the processes for making polymers involve the removal of volatiles to the levels of parts per million (devolatilization). During this step the volatiles are phase separated out of the polymer through a combination of heating and applying lower pressure, creating foam with the pure polymer in liquid phase and the volatiles in the gas phase. The efficiency of the devolatilization process depends on predicting the onset of solvent phase change in the polymer and volatiles mixture accurately based on the processing conditions. However due to the complex relationship between the polymer properties and the processing conditions this is not trivial. In this work, a bubble scale model is coupled with a bulk scale transport model to simulate the processing conditions of polymer devolatilization. The bubble scale model simulates the nucleation and bubble growth based on the classical nucleation theory and the popular ``influence volume approach.'' As such it provides the information of bubble size distribution and number density inside the polymer at any given time and position. This information is used to predict the bulk properties of the polymer and its behavior under the applied processing conditions. Initial results of this modeling approach will be presented. [Preview Abstract] |
Monday, November 24, 2014 9:05AM - 9:18AM |
G4.00006: Towards Modeling Local Foam Drainage Using the Arbitrary Lagrangian Eulerian Method Andrew Brandon, Ramagopal Ananth Liquid drainage in foams is a multi-scale, multi-dimensional phenomena that is tied directly to how well a foam performs. For example, the amount of metal within a metal foam after it solidifies affects the strength of the foam and the amount of liquid within an aqueous fire fighting foam determines how effective it is at extinguishing a fire. Liquid drainage is driven by gravity and is governed by the liquid's density and viscosity as well as the surface tension at the liquid gas interface. There are numerous one dimensional, single phase models that approximate liquid drainage by employing a global description but there are no multidimensional models that use a local description. In this presentation, I will describe an ongoing effort to develop a two dimensional, multiphase, Arbitrary Lagrangian Eulerian model for the study of local liquid drainage in foams. I will present an improved algorithm for the solution of the incompressible fluid equations in the Arbitrary Lagrangian Eulerian method, the novel method used for moving the domain in time, and results from this model development effort. [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G4.00007: Blast wave mitigation by liquid foam Martin Monloubou, Benjamin Dollet, Arnaud Saint-Jalmes, Isabelle Cantat Due to their high apparent viscosity, liquid foams are good systems to absorb energy. This property is for instance used in the military domain to mitigate blast waves or explosions [Britan, 2009; Del Prete, 2013]. However, the underlying dissipation mechanisms are still not well understood. We address this issue by resolving in space and time a shock wave impacting a foam sample. We use a shock tube to send a shock wave on a foam with controlled liquid fraction, bubble size and physico-chemistry. The impacting shock creates an expanding cavity in the foam and propagates through the whole sample. The dynamics is recorded with a high speed camera and pressure signals are simultaneously measured. We show the influence of the bubble size and of the shock amplitude on the velocity and on the attenuation of the pressure signal, and on the foam destruction rate.\\[4pt] [1] Britan et al., Colloids and Surfaces A, 344:48-55, 2009.\\[0pt] [2] Del Prete et al., Shock Waves, 23:39-53, 2013. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G4.00008: Pinch-off Scaling Law of Soap Bubbles John Davidson, Sangjin Ryu Three common interfacial phenomena that occur daily are liquid drops in gas, gas bubbles in liquid and thin-film bubbles. One aspect that has been studied for these phenomena is the formation or pinch-off of the drop/bubble from the liquid/gas threads. In contrast to the formation of liquid drops in gas and gas bubbles in liquid, thin-film bubble pinch-off has not been well documented. Having thin-film interfaces may alter the pinch-off process due to the limiting factor of the film thickness. We observed the pinch-off of one common thin-film bubble, soap bubbles, in order to characterize its pinch-off behavior. We achieved this by constructing an experimental model replicating the process of a human producing soap bubbles. Using high-speed videography and image processing, we determined that the minimal neck radius scaled with the time left till pinch-off, and that the scaling law exponent was 2/3, similar to that of liquid drops in gas. [Preview Abstract] |
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