Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session V29: Foams and Emulsions |
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Sponsoring Units: DFD Chair: Douglas Durian, University of Pennsylvania Room: Colorado Convention Center 303 |
Thursday, March 8, 2007 11:15AM - 11:27AM |
V29.00001: Coarsening in steady-state aqueous foam Klebert Feitosa, Douglas J. Durian We perform an experiment with a column of aqueous foam maintained in steady-state by a constant gas flow rate at the bottom. In steady-state we measure the bubble velocity $u$, bubble radius $R_{32}$ and liquid fraction $\varepsilon$ in the foam as a function of height. Away from the bottom, capillary effects are negligible and the liquid fraction profile, set by the balance of viscous forces and gravity, does not change with time. Taking the liquid fraction as a given, the gas transport is investigated. We find that the bubbles rise with constant speed equals to the measured gas flux and coarsen as a function of height. We measure the coarsening rate for almost three decades in liquid fraction combining data from steady-state and free drainage experiments. The results show that the coarsening rate grows without bound proportional to $1/\sqrt{\varepsilon}$ for the entire range of liquid fractions. [Preview Abstract] |
Thursday, March 8, 2007 11:27AM - 11:39AM |
V29.00002: Polymorphism in Monodisperse Foams Olivia L. Halt, Randall D. Kamien The aging of dry foams combines the local requirements of Plateau's rules and surface to volume relations with the global requirement of volume conservation. In a wet foam, the size of each spherical bubble is directly related to its radius of curvature, $R$. For dry foams, however, we must instead consider the mean curvature, $H$, which controls gas diffusion but is not directly related to the bubble size. Using a mean-field approach, our model connects distributions of mean curvature to distributions of cell size. This conversion makes use of mean field bubbles [1,2]. By considering the positive and negative curvature distributions separately, such that the cells have equal surface area, we obtain an average number of faces close to previously measured values. Also, distributions of cell sizes are obtained that are seen in real foam. \newline \newline [1] Glicksman M., Phil. Mag., 85 (2005) 3. \newline [2] Hilgenfeldt S., Kraynik A., Reinelt D., and Sullivan J. Europhys. Lett. 67 (2004) 484. [Preview Abstract] |
Thursday, March 8, 2007 11:39AM - 11:51AM |
V29.00003: Rheology of wet foams of different bubble sizes and surfactant chemistry Stephan Koehler, Raenell Soller We present a new rheological technique for measuring the mechanical properties of aqueous foams at different liquid volume fractions, and of different surfactant compositions. We also cosider the influence of particulate matter on the rheology. We find that at high shear rates the liquid drainage rates are diminished. [Preview Abstract] |
Thursday, March 8, 2007 11:51AM - 12:03PM |
V29.00004: Flow of soft glassy materials in confined geometry Julie Goyon, Annie Colin In this work, we address the question of the flow soft glassy materials in confined geometry. A transparent direct concentrated emulsion of micrometric size flows in a microfluidic channel under a constant applied drop of pressure. The continuous phase or the dispersed phase is seeded with some sub-micrometric fluorescent latex beads. Taking successive pictures of the flow and correlating them allows us to get the velocity profile. We use rectangular micro-channels with high ratio aspect. The experimental data are analysed in the framework of the lubrication. On one hand, the shear stress is calculated thanks to the position in the channel and the pressure. On the other hand, the shear rate is obtained thanks to the slope in the velocity profile. We point out that the flow cannot be described using a unique behaviour law. Indeed, it is perturbed by rearrangements events which induce three-dimensional flows. These events occur preferentially in the vicinity of the wall where they modify and increase locally the velocity. A comprehensive study of the statistics of the rearrangements events is presented. The role of the drop of pressure, the liquid fraction of the emulsion, the droplet size of the emulsion and the attractive forces between droplets are studied. . [Preview Abstract] |
Thursday, March 8, 2007 12:03PM - 12:15PM |
V29.00005: Novel Shear Banding in 2D Foam Probes Soap Film Friction James Glazier, Ariel Balter, Rebecca Perry A flowing 2D foam (a single layer of bubbles between two glass plates), experiences dissipation from two sources: soap flims moving against the glass plates and soap flims moving against each other. We present preliminary results showing how a new type of shear banding helps us study these various drag forces. We experimentally generate a shear band by injecting air part way along a flowing bubble field in a narrow Hele-Shaw cell. The injected air inflates bubbles as they flow by. These bubbles form an independently flowing channel down the middle of the Hele-Shaw cell. The width and velocity of this channel appear to be selected by the system minimizing the total dissipation. We propose a simple model that agrees with the experimental data. Also, numerical simulations using the Cellular Potts Model ({\it CPM}) software {\it CompuCell3D} appear to faithfully reproduce this shear band phenomenon. Agreement between our expeirment and simulations provide support for {\it CPM} methods for studying foam rheology. [Preview Abstract] |
Thursday, March 8, 2007 12:15PM - 12:27PM |
V29.00006: ABSTRACT HAS BEEN MOVED TO A29 |
Thursday, March 8, 2007 12:27PM - 12:39PM |
V29.00007: Entropically Driven Colloidal Assembly in Emulsions Keng-hui Lin, Liang-jie Lai, Hui Chen Using the techniques developed by Manoharan [1], we encapsulate small numbers of colloidal microspheres and polymers in oil-in-water emulsion droplets, remove the oil and generate colloidal clusters covered with polymers. We observe two types of arrangement in the clusters. The first kind is the same as the type reported in [1] of which the clusters are formed without polymer. The second kind is the same as the structure reported in [2] of which the clusters are formed by binary colloidal microspheres. The polymers we put in the emulsions induce depletion interactions between colloidal particles. We will show that two types of structures are from the interplay between the depletion interactions and surface tension. [1] Manoharan, Elsesser, Pine, \textit{Science} \textbf{301}, 483(2003). [2] Cho \textit{et al. JACS} \textbf{127}, 15968 (2005). [Preview Abstract] |
Thursday, March 8, 2007 12:39PM - 12:51PM |
V29.00008: Rheology of solid-stabilized emulsions Kosta Ladavac, Rodrigo Guerra, Pabitra Sen, David Weitz Concentrated emulsions can possess strong shear rigidity, in spite of being comprised solely of fluids. When stress is applied the drops deform, create additional surface area and are able to store energy. For surfactant-stabilized emulsions this elasticity is driven by surface tension alone. In case of sollid- stabilized emulsions, where droplets are protected by colloidal particles adsorbed at the interfaces, organization of particles and their rigidity leads to a different response to deformation. We study this packing of a packing -- the interplay between 3D structure of emulsion droplets and 2D structure of colloidal particles at their interfaces. [Preview Abstract] |
Thursday, March 8, 2007 12:51PM - 1:03PM |
V29.00009: Flow of colloidal gels through constrictions Jacinta Conrad, Jennifer Lewis We use confocal microscopy to investigate the flow behavior of colloidal gels through constrictions of varying geometry. We flow suspensions of attractive silica colloids through microchannels containing a single constriction point. As the colloid volume fraction is increased, the colloids in the microchannels jam and form a clog. Here we investigate the flow properties and the clogging as a function of applied pressure, microchannel geometry, and the colloid volume fraction. [Preview Abstract] |
Thursday, March 8, 2007 1:03PM - 1:15PM |
V29.00010: Non-affine bubble motion in a two-dimensional, linearly sheared foam Matthias Mobius, Gijs Katgert, Martin van Hecke Two-dimensional foams are an excellent model system to study the non-affine deformations of a disordered, jammed medium under shear. In our experiment we apply linear shear to a monolayer of bubbles that is confined between a soap solution and a glass plate. Through video imaging we track the motion of individual bubbles. We characterize the non-affine motion by looking at the distribution of relative displacement angles, $\alpha$, of neighboring bubbles [1]. A peak at 90 degrees emerges, which corresponds to bubbles sliding past each other. We investigate the change of the probability distribution of this angle, $P(\alpha)$, as a function of liquid fraction and shear rate. We discuss $P(\alpha)$ in the context of the jamming transition and show that near the transition the bubble motion is dominated by sliding. Moreover, we look at the relationship between the local velocity fluctuations and the shear rate. [1] W. Ellenbroek et al. , accepted for Phys.Rev.Lett. [Preview Abstract] |
Thursday, March 8, 2007 1:15PM - 1:27PM |
V29.00011: Thermal conductivity measurements in a 2D Yukawa system V. Nosenko, A. Ivlev, S. Zhdanov, G. Morfill, J. Goree, A. Piel Thermal conductivity was measured for a 2D Yukawa system. First, we formed a monolayer suspension of microspheres in a plasma, i.e., a dusty plasma, which is like a colloidal suspension, but with an extremely low volume fraction and a partially-ionized rarefied gas instead of solvent. In the absence of manipulation, the suspension forms a 2D triangular lattice. To melt this lattice and form a liquid, we used a laser-heating method. Two focused laser beams were moved rapidly around in the monolayer. The kinetic temperature of the particles increased with the laser power applied, and above a threshold a melting transition occurred. We used digital video microscopy for direct imaging and particle tracking. The spatial profiles of the particle kinetic temperature were calculated. Using the heat transport equation with an additional term to account for the energy dissipation due to the gas drag, we analyzed the temperature distribution to derive the thermal conductivity. [Preview Abstract] |
Thursday, March 8, 2007 1:27PM - 1:39PM |
V29.00012: Experimental microrheology of quiescent soap films Vikram Prasad, Eric R. Weeks A soap film consists of a thin water layer that is separated from two bulk air phases above and below it by surfactant monolayers. Previous experiments (Prasad, Koehler and Weeks, PRL 2006) have shown that the coupling between an interface and an infinite bulk fluid is set by a length scale, the ratio between the interfacial viscosity and the bulk viscosity (of order microns to millimeters). This length scale determines the nature of the flow field in the interface and the adjoining bulk phases. In the case of soap films, the thickness of the water layer is an additional length scale, and therefore the exact nature of the coupling between the thin water layer, the surfactant interface and the bulk air phases is unclear. In order to determine this coupling, we use polystyrene spheres as tracer particles and track their motion in the soap films, using both one-and two-particle microrheology. The experimental results are compared to theory, and the consequences for the hydrodynamics of interfaces are discussed. [Preview Abstract] |
Thursday, March 8, 2007 1:39PM - 1:51PM |
V29.00013: Janus particles on colloidosomes (Pickering emulsions) and the role of added surfactant Shan Jiang, Liang Hong, Steve Granick We describe systematically the synergy between particle and surfactant in stabilizing colloidosomes. Special attention is given to what determines the inversion between O/W and W/O emulsions, the so-called `catastrophic phase inversion'. At the onset of the catastrophic phase inversion, we find an exceptional double-emulsion structure. Extending this idea, we find that when the dispersed phase is frozen by lowering the temperature below its solid-liquid phase transition, particles can be locked at the interface and further chemically modified into Janus colloidal particles. This affords an easy way to produce Janus colloidal particles with versatile chemical makeup in large quantity. [Preview Abstract] |
Thursday, March 8, 2007 1:51PM - 2:03PM |
V29.00014: Observing asphaltene aggregation by NMR spectroscopy and relaxation Yi-Qiao Song, Andrew Pomerantz, Kosta Ladavac, Pabitra Sen Asphaltenes are a class of molecules commonly found in the oilfield and defined by their simultaneous solubility in toluene and insolubility in hexanes. The aggregation dynamics of asphaltenes is currently poorly understood but presents a serious problem to the oil industry because aggregation can clog flow though pipelines and the oil-bearing rocks. Recently, aggregation dynamics of asphaltenes at very low concentration was measured by nuclear magnetic resonance (NMR) of spin-spin relaxation and diffusion, and fluorescence correlation spectroscopy (FCS). Here, asphaltene aggregation at higher concentrations is observed by monitoring the NMR spectroscopy and longitudinal relaxation times (T1) of the solvent protons. These measurements shed new light on the dynamics of aggregation. [Preview Abstract] |
Thursday, March 8, 2007 2:03PM - 2:15PM |
V29.00015: Towards a 2D nonperiodic Solid Xiaochao Xu, David Pine We report on an experimental study of the two-dimensional phase behavior of colloidal dumbbells (dimers) trapped at a water-oil interface. The dimers are made out of $1.0\,\mu {\rm m}$ silica microspheres that are fused together at a point. The water-oil interface is very slightly concave so that the dimers are gently compressed by gravity towards the center of interface. The spheres form a stable dense state after a few days. The pair correlation function of single spheres exhibits order on a length scale of about 10 particle diameters. We report on the translational and orientational order of the dumbbells as a function of particle density. [Preview Abstract] |
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