Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L6: Surface Tension Effects: Marangoni, Particles and GeneralInterfacial
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Chair: Andrew Dickerson, University of Central Florida Room: 406 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L6.00001: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 4:18PM - 4:31PM |
L6.00002: Evaporation-driven Marangoni Transport of Particles over Free Surface: A Potential Window into Vapor Recoil Forces and Self-rewetting Pool Boiling Alexander Yarin, Abhilash Sankaran Experiments were conducted using liquids evaporating from Petri dish. Spatio-temporal variation of temperature on the liquid surface was measured using infrared imaging, which revealed significant temperature reduction (a stronger evaporation) toward the center. This drives strong Marangoni flow toward the center. A model is developed for the thermal-Marangoni convection due to non-uniform cooling of the free surface of liquid in an open vessel. In particular, an analytical solution of the plane problem in creeping flow approximation is found using the Goursat complex potential technique for the biharmonic equation for stream function. The velocity field of such thermocapillarity-driven motion was thus predicted and compared to experimental data. In the experiments, buoyant particles were located at periphery of free surface, entrained by the Marangoni convection, and their motion tracked. Velocities of particle motion and their trajectories were measured. The wiggling trajectories were observed and discussed in the framework of vapor recoil force. Experiments with different liquids were conducted including water--heptanol mixtures. The latter are important to elucidate self-rewetting phenomena, which allow one to intensify heat removal in pool boiling. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L6.00003: Marangoni and Gibbs elasticity of flowing soap films Ildoo Kim, Aakash Sane, Shreyas Mandre A flowing soap film has two elasticities. Marangoni elasticity dynamically stabilizes the film from sudden disturbance, and Gibbs elasticity is an equilibrium property that influences the film's persistence over time. In our experimental investigation, we find that Marangoni elasticity is 22 mN/m independent of the film thickness. On the other hand, Gibbs elasticity depends both on the film thickness and the soap concentration. Interestingly, the soap film made of dilute soap solution has the greater Gibbs elasticity, which is not consistent to the existing theory. Such discrepancy is originated from the flowing nature of our soap films, in which surfactants are continuously replenished. [Preview Abstract] |
Monday, November 20, 2017 4:44PM - 4:57PM |
L6.00004: Rotational Motion of Axisymmetric Marangoni Swimmers Jonathan Rothstein, Nick Uvanovic A series of experiments will be presented investigating the motion of millimeter-sized particles on the surface of water. The particles were partially coated with ethanol and carefully placed on a water interface in a series of Petri dishes with different diameters. High speed particle motion was driven by strong surface tension gradients as the ethanol slowly diffuses from the particles into the water resulting in a Marangoni flow. The velocity and acceleration of the particles where measured. In addition to straight line motion, the presence of the bounding walls of the circular Petri dish was found to induce an asymmetric, rotational motion of the axisymmetric Marangoni swimmers. The rotation rate and radius of curvature was found to be a function of the size of the Petri dish and the curvature of the air-water interface near the edge of the dish. For large Petri dishes or small particles, rotation motion was observed far from the bounding walls. In these cases, the symmetry break appears to be the result of the onset of votex shedding. Finally, multiple spherical particles were observed to undergo assembly driven by capillary forces followed by explosive disassembly. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L6.00005: Mobility of Yield-Stress Fluids on Lubricant-Impregnated Surface Leonid Rapoport, Brian Solomon, Kripa Varanasi Assuring the flow of yield-stress fluids is an essential problem for various industries such as consumer products, health care, and energy. Elimination of wall-induced pinning forces can potentially save power and cleaning costs as well as enable the flow of yield-stress fluids in channels previously considered too narrow. Lubricant-Impregnated Surfaces (LIS) have been demonstrated to change the dynamic behavior of yield-stress fluids and enable them to move as bulk without shearing at all. However, despite the wide applicability of this technology and its general appeal, the fundamental principles governing the performance of yield stress fluids on LIS have not yet been fully explained. In this work, we explore the mobility of yield stress fluids on a wide range of LIS, and explain the connection between macroscale behavior and the microscale properties of the LIS. Specifically, we show a striking difference in mobility between an LIS that contains a lubricant which fully spreads on the rough micro-features of the surface, and an LIS that contains a lubricant which only imbibes these features but does spread over them [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L6.00006: Effective dilution of surfactants due to thinning of the soap film. Aakash Sane, Shreyas Mandre, Ildoo Kim A flowing soap film is a system whose hydrodynamic properties can be affected by its thickness. Despite abundant experiments performed using soap films, few have examined the dependence of its physical as well as chemical properties with respect to its thickness. We investigate one such property - surface tension of the flowing film and delineate its dependence on the concentration of the soap solution and flow rate per unit width i.e. thickness of the soap film. Using our proposed method to measure the average surface tension in-situ over the whole soap film, we show that the surface tension increases by reducing the thickness of the film and by reducing the concentration of the soap solution. Our data suggests that thinning of the soap film is effectively diluting the solution. Thinning increases the adsorption of surfactants to the surfaces, but it decreases the total number of molecules per unit area. Our work brings new insight into the physics of soap films and we believe that this effective dilution due to thinning is a signature of the flowing soap films, whose surface concentration of surfactants is affected by the thickness. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L6.00007: Capillary trapping of particles in thin-film flows Emilie Dressaire, Michael Gomez, Benedicte Colnet, Alban Sauret When a thin layer of suspension flows over a substrate, some particles remain trapped on the solid surface. When the thickness of the liquid layer is comparable to the particle size, the particles deform the liquid interface, which leads to local interactions. These effects modify the transport of particles and the dynamics of the liquid films. Here, we characterize how capillary interactions affect the transport and deposition of non-Brownian particles moving in thin liquid films and the resulting loss of transported material. We focus on gravitational drainage flows, in which the film thickness becomes comparable to the particle size. Depending on the concentration of particles, we find that the drainage dynamics exhibits behavior that cannot be captured with a continuum model, due to the deposition of particles on the substrate. [Preview Abstract] |
Monday, November 20, 2017 5:36PM - 5:49PM |
L6.00008: Numerical Analysis of Puddle Jumping from Hydrophobic Surface A. Avhad, T. Jubaree, L. Torres, M. Weislogel, H. Tan Drop tower experiments have shown that the liquid puddle can jump from a hydrophobic surface due to absence of gravity. A numerical analysis is carried out to study the puddle jump using an open source computational fluid dynamics code Gerris. The puddle jump of distilled water from both flat base and dished (curved) base hydrophobic surfaces are investigated in our study. The puddle volume varies from 0.03 ml to 100 ml in the previous experimental study. Simulation results including jump velocity, jump time and droplet profile at given times are compared against experiments for validation. The droplet profile, average jump velocity, total energy, jump time and Contact Angle Hysteresis results differ for puddle jump from flat base and dished base. The reason for such difference has been discussed in the study. The energy budget and dissipation mechanisms are studied for some cases. Viscous dissipation has been found to play an important role in jump dynamics, especially before the drop takes-off from surface. The dominating individual viscous dissipation term is different for drop jumping off from flat base and dished base. Furthermore, we also investigate the smallest droplet that can jump off from the surface. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L6.00009: Dip-coating in a suspension: entrainment of particles Alban Sauret, Benedicte Colnet, Guillaume Saingier, Howard Stone, Martin Bazant, Emilie Dressaire Withdrawing an object from a suspension can lead to the entrainment of particles on the solid surface. When unwanted, such particle trapping is associated with the contamination of the solid surface, but it can also be leveraged to design new materials. To study the entrainment of particles during the dip-coating, we focus on a model approach, in which a solid plate is withdrawn from a bath of hard spheres in suspension. We observe different regimes depending on the withdrawal velocity and we experimentally characterize the number density of particles trapped on the solid plate. Surprisingly, our results show that there is a critical velocity below which no particles are entrained. The experimental findings are rationalized to predict the critical velocity below which no particles are entrained on the plate. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L6.00010: Contact lines on silicone elastomers promote contamination Aurelie Hourlier-Fargette, Arnaud Antkowiak, Sebastien Neukirch Silicone elastomers are used in contact with aqueous liquids in a large range of applications. Due to numerous advantages such as its flexibility, optical transparency, or gas permeability, polydimethylsiloxane is widely spread in rapid prototyping for microfluidics or elastocapillarity experiments. However, silicone elastomers are known to contain a small fraction of uncrosslinked low-molecular-weight oligomers, the effects of which are not completely understood. We show that in various setups involving an air-water-silicone elastomer contact line, a capillarity-induced extraction of uncrosslinked oligomers occurs, leading to a contamination of water-air interfaces. We investigate the case of a static air-water-PDMS contact line, before focusing on moving contact lines. A water droplet sliding down on a PDMS inclined plane or an air bubble rising on an immersed PDMS plane exhibits two successive speed regimes: the second regime is reached only when a monolayer of oligomers completely covers the water-air interface. These experiments involve processes occurring at the polymer network scale that have significant macroscopic consequences, and therefore provide a simple test to evaluate the presence of uncrosslinked oligomers in an elastomer sample. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L6.00011: On the reduction of splash-back Andrew Dickerson, Jeremy Stephen The reduction of splash height following the impact of a solid body on a liquid surface is relevant to multiple sectors including military missile entry, industrial processing, and visits to public restrooms. While most studies have viewed splashes in the context of control of impactor shape and surface properties, we here consider the effects of splash height following modification of a liquid surface by surfactants and thin fabrics. Smooth, hydrophilic, free-falling spheres are allowed to impact a quiescent liquid surface of modified surface conditions while filmed with a high-speed camera. We measure splash heights and cavity depths formed by impacting spheres across Froude numbers 3 - 6.5. As expected, lowering the surface tension of the liquid increased splash height with respect to pure water. The introduction of fabric to the surface has an more unpredictable effect. With respect to unaltered impact conditions, ample inclusion of fabric on the surface reduces splash height, while a meager amount of fabric amplifies splashing due to the augmentation of cavity formation preceding a Worthington jet. [Preview Abstract] |
Monday, November 20, 2017 6:28PM - 6:41PM |
L6.00012: Contact angle hysteresis in a microchannel: statics Metin Hatipogullari, Christophe Wylock, Marc Pradas, Serafim Kalliadasis, Pierre Colinet We study contact angle hysteresis by tracking static meniscus configurations upon varying the volume of a liquid inside a chemically heterogeneous microchannel. We first construct a graphical force balance similar to the classical theory of Joanny and de Gennes [1] for this system, though here with a straight contact line (2D channel). Hysteresis is induced by wettability gradients above a finite threshold value. This is also visualized in a phase plot enabling to easily predict stick-slip events of the contact line and the occurrence of hysteresis. Above the threshold and for non-overlapping Gaussian defects, we find good agreement with the classical formulas for the hysteresis amplitude induced by a dilute system of defects. In particular it is found to be proportional to the square of the defect force and to the defect concentration. For a sinusoidal heterogeneity, decreasing the ratio between the heterogeneity wavelength and the microchannel gap size, brings the system from a sub threshold regime, to a stick-slip dominated regime, and finally to a regime with a quasi-constant advancing and receding angle. In the latter, the hysteresis amplitude is found to be proportional to the defect force. \newline \newline [1] P.G. Joanny and J.F. de Gennes, J. Chem. Phys. 81: 552 (1984). [Preview Abstract] |
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