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 H2: Surface Tension Effects: General |
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Chair: John Lister, University of Cambridge Room: 3002 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H2.00001: Modelling two-phase slug self-propulsion in a capillary Mathieu Sellier, Irshad Khodabocus, Volker Nock, Claude Verdier We present a numerical study of the flow of a droplet of two miscible fluids juxtaposed in a capillary tube. We show that the asymmetry of the system results in the spontaneous motion of the composite droplet which can be of potential use in microfluidics applications or for transport in porous media. We also show that the droplet motion is sustained until the miscible fluids have become fully mixed. The proposed numerical model is implemented in COMSOL Mutiphysics using the Laminar Two-Phase Flow Phase Field Method coupled with an advection-diffusion chemical concentration equation. The results are validated using experimental data from Reference 1 and explained in the context of a simplified phenomenological model. An important benefit of the simulation is the ability to investigate the transient behaviour composite droplet and the development of the internal flow features in the system which could allow the development of optimized systems. \\[4pt] [1] Bico, J., Qu\'{e}r\'{e}, D., Liquid trains in a tube, \textit{Europhys. Lett.}, \textbf{51(5)}, 546 (2000) [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H2.00002: Viscous peeling with capillary suction Gunnar Peng, John Lister If an elastic tape is stuck to a rigid substrate by a thin film of viscous fluid and then peeled off by pulling at a small angle to the horizontal, then both viscous and capillary forces affect the peeling speed (McEwan and Taylor, 1966). If there is no capillary meniscus (e.g. if the peeling is due to viscous fluid being injected under the tape), then the peeling speed is given by a Cox--Voinov-like law, and is an increasing function of the peeling angle. We show that, with a meniscus present, the effect of the capillary forces is to suck down the tape, reducing the effective peeling angle and hence the peeling speed. When surface tension dominates and the peeling speed tends to zero, the system transitions to a new state whose time-evolution can be described by a system of coupled ordinary differential equations. These asymptotic results are confirmed by numerical calculations. Similar results hold for the peeling-by-bending of elastic beams, with ``angle'' replaced by ``curvature'' (i.e. bending moment). [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H2.00003: Painting Pictures with Whisky Hyoungsoo Kim, Fran\c{c}ois Boulogne, Eujin Um, Ian Jacobi, Howard Stone Have you ever looked at the dried mark of whisky on the glass? While the whisky evaporates, various solid components inside the whisky are deposited with a peculiar pattern, which creates a beautiful picture. This particle patterning is induced by the solutal Marangoni effect. We investigate this effect on both the flow behavior and the particle deposition patterns in binary-mixture droplet evaporation by varying the concentration ratio between ethanol and water. To visualize the particle and fluid motion, we perform Particle Image Velocimetry. We observe that at the beginning stage complex circulating flow patterns occurred, which are triggered by the surface tension gradient, i.e. Marangoni effect. Ethanol first evaporates due to the lower vapor pressure compared to water. When the ethanol has vanished, a radial flow pattern is observed. Furthermore, we find that as the initial ethanol concentration increases, the mobility of the receding contact line increased. At high ethanol concentrations, the contact line kept receding so as to draw groups of particles that deposited in an annular pattern. We thank Ernie Button for sharing with us many beautiful images of whisky after it had dried. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H2.00004: Capillary Flows along Open Channel Conduits: the Open-Star Section Mark Weislogel, Yongkang Chen, Thanh Nguyen, John Geile, Michael Callahan Capillary rise in tubes, channels, and grooves has received significant attention in the literature for over 100 years. In yet another incremental extension of related work, a transient capillary rise problem is solved for spontaneous flow along an interconnected array of open channels forming what is referred to as an ``open-star'' section. This geometry possesses several attractive characteristics including passive phase separations and high diffusive gas transport rates. Despite the complex geometry, novel and convenient approximations for capillary pressure and viscous resistance enable closed form predictions of the flow. As part of the solution, a combined scaling approach is applied that identifies unsteady-inertial-capillary, convective-inertial-capillary, and visco-capillary transient regimes in a single parameter. Drop tower experiments are performed employing 3-D printed conduits to corroborate all findings. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H2.00005: Characteristics of air entrainment during dynamic wetting failure along a planar substrate Satish Kumar, Eric Vandre, Marcio Carvalho We report results of experiments characterizing the onset of air entrainment during dynamic wetting failure along a planar substrate (J. Fluid Mech. 747 (2014) 119). Using high-speed video, dynamic contact line (DCL) behavior is recorded as a tape substrate is drawn through a bath of a glycerol/water solution. Air entrainment is identified by triangular air films that elongate from the DCL above a critical substrate speed. Meniscus confinement between the substrate and a stationary plate delays air entrainment to higher speeds for a wide range of liquid viscosities. Liquid pressurization moves the meniscus near a sharp corner, changing its shape and further postponing air entrainment. Meniscus shapes recorded near the DCL demonstrate that smaller entrained air films appear in the more viscous solutions. Regardless of size, air films become unstable to thickness perturbations and ultimately rupture, leading to entrainment of air bubbles. Recorded critical speeds and air-film sizes compare well to predictions from a hydrodynamic model for dynamic wetting failure, indicating that strong air stresses near the DCL trigger the onset of air entrainment. The results suggest strategies for postponing air entrainment, which often limits the maximum speed of industrial coating processes. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H2.00006: Shallow flows over surfaces of patterned wettability Morgane Grivel, David Jeon, Morteza Gharib Our previous work showed that surfaces with spatially patterned wetting properties induce passive displacements of shallow flows. Polycarbonate plates were patterned with hydrophobic and hydrophilic stripes, and a thin, rectangular water jet impinged on the patterned surface. We reported development of intriguing roller structures at the hydrophobic-hydrophilic interfaces. In our present work, we study the effect of varying the stripes' width, spacing, and orientation on the dynamics of these roller structures. Specifically, we are interested in the vortex generation and air entrainment by the rollers. We report quantitative results to this effect. We will also discuss potential uses of this technique for modifying contact line dynamics and bow waves near ships. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H2.00007: Capillary-Inertial Colloidal Catapult upon Drop Coalescence Roger Chavez, Fangjie Liu, James Feng, Chuan-Hua Chen To discharge micron-sized particles such as colloidal contaminants and biological spores, an enormous power density is needed to compete against the strong adhesive forces between the small particles and the supporting surface as well as the significant air friction exerted on the particles. Here, we demonstrate a colloidal catapult that achieves such a high power density by extracting surface energy released upon drop coalescence within an extremely short time period, which is governed by the capillary-inertial process converting the released surface energy into the bulk inertia of the merged drop. When two drops coalesce on top of a spherical particle, the resulting capillary-inertial oscillation is perturbed by the solid particle, giving rise to a net momentum eventually propelling the particle to launch from the supporting surface. The measured launching velocity follows a scaling law that accounts for the redistribution of the momentum of the merged drop onto the particle-drop complex, and is therefore proportional to the capillary-inertial velocity characterizing the coalescing drops. The interfacial flow process associated with the colloidal catapult is elucidated with both high-speed imaging and phase-field simulations. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H2.00008: Translational and rotational diffusion of Janus nanoparticles at liquid interfaces Hossein Rezvantalab, Shahab Shojaei-Zadeh We use molecular dynamics simulations to understand the thermal motion of nanometer-sized Janus particles at the interface between two immiscible fluids. We consider spherical nanoparticles composed of two sides with different affinity to fluid phases, and evaluate their dynamics and changes in fluid structure as a function of particle size and surface chemistry. We show that as the amphiphilicity increases upon enhancing the wetting of each side with its favored fluid, the in-plane diffusivity at the interface becomes slower. Detail analysis of the fluid structure reveals that this is mainly due to formation of a denser adsorption layer around more amphiphilic particles, which leads to increased drag acting against nanoparticle motion. Similarly, the rotational thermal motion of Janus particles is reduced compared to their homogeneous counterparts as a result of the higher resistance of neighboring fluid species against rotation. We also incorporate the influence of fluid density and surface tension on the interfacial dynamics of such Janus nanoparticles. Our findings may have implications in understanding the adsorption mechanism of drugs and protein molecules with anisotropic surface properties to biological interfaces including cell membranes. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H2.00009: Driven interfacial particles acting as capillary dipoles Aaron Doerr, Steffen Hardt Solid particles attached to fluid-fluid interfaces exhibit a number of interesting phenomena such as the formation of regular crystal-like structures. The underlying particle-particle interactions as well as their various origins have been the subject of many studies mainly covering static situations. By contrast, the case of driven particles moving along a fluid-fluid interface is still widely unexplored. By means of perturbation methods we demonstrate that such particles cause a dipolar interfacial deformation which decays algebraically with distance from the particle center. In our study, we focus on particles at interfaces between two fluids of high viscosity ratio, equilibrium contact angles close to 90$^\circ$, and a pinned three-phase contact line. It is shown that the moving particles change their orientation with respect to the interface normal at zero velocity, similar to the occurrence of a trim angle in ship hydrodynamics. The corresponding interfacial deformation gives rise to an direction-dependent particle-particle interaction which can be approximated via linear superposition in the case of large separations relative to the particle diameter. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H2.00010: Collapse and sinking of self-assembled sphere clusters on a liquid-liquid interface Steven Jones, Niki Abbasi, Abhinav Ahuja, Vivian Truong, Scott Tsai The self-assembly of objects on a liquid-liquid interface is a phenomenon that has attracted a lot of attention. When a single settling sphere has insufficient gravitational energy to break through a liquid-liquid interface, multiple spheres can self-assemble on the interface, by capillary and buoyancy forces, to form a cluster. If a sphere cluster's gravitational energy overcomes the interfacial tension energy barrier of the liquid-liquid interface, the cluster will sink through the interface. Here we show with experiments that small spheres approaching an oil-water interface will self-assemble into clusters, and at a critical size pass through the interface. We demonstrate that the size of a sphere cluster at the time of interface breakthrough can be controlled by altering the sphere radius and the liquid-liquid interfacial tension. We also find that the critical cluster size changes depending on the way the spheres are deposited: spheres deposited into a monolayer raft configuration will sink though the interface as a larger cluster than spheres stacked into a spheroidal geometry. We find that the number of spheres in each sinking cluster scales with power-laws of the Bond number, and we observe different power-laws for raft and stack cluster configurations. [Preview Abstract] |
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