Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W12: Foams and Suspensions |
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Sponsoring Units: DFD Chair: Dan Blair, Georgetown Univeristy Room: B110-B111 |
Thursday, March 18, 2010 11:15AM - 11:27AM |
W12.00001: Rheology of a dilute suspension of cubic nanoparticles Rajesh Kumar Mallavajula, Donald Koch, Lynden Archer The rheological properties of suspensions of Brownian cube-shaped particles are interesting because of the greater increase in the translational freedom caused by layering relative to suspensions of Brownian spheres. As a first step toward understanding suspensions of these particles, we present theoretical (multipole and finite element) solutions of simple shear flow around an isolated cube and use this solution to obtain the intrinsic viscosity. The stress stress-strain-rate relationship is anisotropic with different particle stresslets when the extensional axis is parallel to an axis or a diagonal of the cube. The suspension viscosity, $\mu_{eff}$, in the limit of zero shear rate can be obtained as an isotropic orientational average, yielding a prediction $\mu _{eff}=\mu $(1+5.45$\phi )$ where $\phi $ is the particle volume fraction and the coefficient 5.45 is the intrinsic viscosity, [ \textit{$\eta $} ] of the cube. The calculated [ \textit{$\eta $} ] for cubes is therefore more than twice that computed by Einstein, [ \textit{$\eta $} ] = 2.5, for spheres. To evaluate our prediction, we have synthesized cube-shaped Fe$_{3}$O$_{4}$ particles and characterized their rheological properties in dilute suspensions. [Preview Abstract] |
Thursday, March 18, 2010 11:27AM - 11:39AM |
W12.00002: Hydrodynamic Interaction of Colloid Suspension in Ribbon Channels Binhua Lin, Sergey Novikov, Stuart A. Rice We report the results of an experimental study of hydrodynamic interaction in colloid suspensions that are intermediate between quasi-one-dimensional (q1D) and quasi-two-dimensional (q2D) systems. Specifically, the systems examined are one-layer deep colloid suspensions confined in ribbon channels with widths from one to twelve particle diameters. The current research follows up our earlier studies of the structure of q1D ribbon colloid suspension as a function of the ribbon width, of pair diffusion in single-file q1D channels and planar q2D colloid suspensions. Given the stratification of the density distribution transverse to the ribbon channel, the pair diffusion coefficient within one stratum behaves as if the colloids are confined in a single-file q1D channel, and the diffusion coefficient does not vary from stratum to stratum across the channel. When the stratification of the transverse density distribution in the ribbon channel is disregarded, the pair diffusion coefficient for the confined suspension differs from that in an infinite q2D suspension. [Preview Abstract] |
Thursday, March 18, 2010 11:39AM - 11:51AM |
W12.00003: Jamming of Solid-Stabilized Emulsions Sujit Datta, Kosta Ladavac, Rodrigo Guerra, David Weitz Emulsions -- metastable suspensions of droplets of one fluid dispersed within another -- can be concentrated over a wide range of volume fractions, due to droplet deformability. Here, we study the rheological properties of solid-stabilized (versus surfactant-stabilized) emulsions over a range of volume fractions. These experiments allow us to explore the role of interfacial effects in determining bulk mechanical behavior, potentially yielding further insight into the elasticity of jammed emulsions. [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:03PM |
W12.00004: ABSTRACT WITHDRAWN |
Thursday, March 18, 2010 12:03PM - 12:15PM |
W12.00005: Liquid organic foams for formulation optimization: an assessment of foam linear viscoelasticity and its temporal dependence Jamie Kropka, Lisa Mondy, Mat Celina Liquid foams are viscoelastic liquids, exhibiting a fast relaxation attributed to local bubble motions and a slow response due to structural evolution of the intrinsically unstable system. In this work, these processes are examined in unique organic foams that differ from the typically investigated aqueous systems in two major ways: the organic foams (1) posses a much higher continuous phase viscosity and (2) exhibit a coarsening response that involves coalescence of cells. The transient and dynamic relaxation responses of the organic foams are evaluated and discussed in relation to the response of aqueous foams. The change in the foam response with increasing gas fraction, from that of a Newtonian liquid to one that is strongly viscoelastic, is also presented. In addition, the temporal dependencies of the linear viscoelastic response are assessed in the context of the foam structural evolution. These foams and characterization techniques provide a basis for testing stabilization mechanisms in epoxy-based foams for encapsulation applications. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 18, 2010 12:15PM - 12:27PM |
W12.00006: Characterization of Intermittent and Continuous Dynamics in Jammed Aqueous Foam Sam Stanwyck, Michael Folkerts, Oleg Shpyrko We use optical laser diffraction in a multi-speckle detection scheme to investigate the mesoscale dynamics in aqueous foam. Using linear correlation and time-resolved correlation, we are able to analyze the slowing down of the rate of bubble rearrangement events during foam aging. We introduce Temporal Contrast Analysis, a novel statistical tool for analyzing these dynamics. Using Temporal Contrast Analysis we are able to show that there are two distinct dynamical components present in the foam: intermittent, avalanche-like dynamics and continuous, flow-like dynamics. We are able to separate these two components from each other and from the intrinsic statistical noise contribution, and independently analyze the slowing down of each component with age. [Preview Abstract] |
Thursday, March 18, 2010 12:27PM - 12:39PM |
W12.00007: The Search for Precursor and Aftershock Dynamics in Aqueous Foam Michael M. Folkerts, Samuel W. Stanwyck, Oleg G. Shpyrko We probe the dynamics of an aqueous foam sample using optical photon correlation spectroscopy. Using a multi-speckle detection scheme to record the changes in a coherent laser speckle pattern, we gain insight into the nature of the dynamics in the foam during the aging process. We introduce Temporal Contrast Analysis, an approach that couples to intermittent, ``avalanche''-like events, and enables us to study the magnitude, duration and temporal spacing of such events. We will discuss the application of Temporal Contrast Analysis to search for precursor and aftershock events that precede or succeed major structural rearrangements in the foam. [Preview Abstract] |
Thursday, March 18, 2010 12:39PM - 12:51PM |
W12.00008: Structural Inhomogeneities in a Dense Emulsion S. K. Dutta, E. D. Knowlton, D. L. Blair A dispersion of emulsion droplets under a shear stress near the jamming transition can be characterized by the distribution of contact forces between neighboring drops. Due to the inherent structural disorder, we expect that during flow, the motion of the particles is highly spatially correlated. We directly access these quantities in a dense oil-in-water emulsion by determining the magnitude and location of deformations on individual droplets. We perform measurements on a dense polydisperse emulsion using a customized confocal rheometer which is capable of simultaneously acquiring three-dimensional images and measuring the bulk viscoelastic properties of a sample with a precise shear. [Preview Abstract] |
Thursday, March 18, 2010 12:51PM - 1:03PM |
W12.00009: Coarsening in Two Dimensional Foams Adam Roth, Christopher Jones, Douglas Durian Coarsening in two dimensional foams is governed by Von Neumann's law, which relates rate of change of size of a bubble to its number of sides. We have built an apparatus that allows us to measure individual bubble statistics, such as area and number of sides, as they coarsen. We can also control the liquid fraction of the foam, which allows us to control the rate of coarsening. We observe correspondence to Von Neumann's law except for a deviation for small bubbles. Small bubbles are observed to coarsen more slowly than expected based on the number of sides. This effect is due to increased local liquid fraction contributed by the Plateau borders. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:15PM |
W12.00010: Structure and dynamics of a coarsening emulsion Klebert Feitosa, John Crocker We investigate the structure and dynamics of a non-aqueous coarsening emulsion. The experiment is performed on an index and density matched emulsion prepared by homogenization with droplets occupying approximately 80\% of the volume fraction. Three dimensional visualizations of the droplets are obtained by fluorescent confocal microscopy at different time intervals as the emulsion coarsens. We find that the droplet size distribution matches a Weibull distribution. The pair coordination function as a function of droplet core size shows a peculiar liquid structure where small droplets fill the interstices between big ones. While we observe self similar behavior in droplet growth, the evolution of the droplet size distribution departs from that predicted by mean field theory. [Preview Abstract] |
Thursday, March 18, 2010 1:15PM - 1:27PM |
W12.00011: Critical transition in fiber suspension Alexandre Franceschini, Elizabeth Guazzelli, David Pine A single buoyant fiber in a low Reynolds shear flow has a fully determined motion, so-called Jeffery orbit. However, the behavior of a concentrated fiber suspension remains unclear; even slight interactions between objects can disturb the system [1]. The non-reversible motion of the fiber suspension in oscillatory flow is monitored with a) quantitative image analysis and b) measurement of the in-phase torque response. A dynamical phase transition from a quasi-reversible state to a fluctuating one is observed as the strain amplitude is increased over a threshold at which the transient time exhibits a power law divergence. We discuss here the nature of this transition and its universality class. The main features of this transition are consistent with earlier results on sphere suspensions [2, 3], such systems might be one of the few realizations of conserved directed percolation [4].\\[4pt] [1] Okagawa A and al, Science, Volume 181, Issue 4095, p159 (1973)\\[0pt] [2] Pine DJ and al, Nature, vol 438, Issue 7070, p997 (2005)\\[0pt] [3] Corte L and al, Nature physics, vol 4, Issue 5, p420 (2008)\\[0pt][4] Menon GI and al, PrE, vol 79, 061108 (2009) [Preview Abstract] |
Thursday, March 18, 2010 1:27PM - 1:39PM |
W12.00012: Viscous properties of aluminum oxide nanotubes and aluminium oxide nanoparticles - silicone oil suspensions Ram Thapa, Steven French, Adrian Delgado, Carlos Ramos, Jose Gutierrez, Mircea Chipara, Karen Lozano Electrorheological (ER) fluids consisting of $\gamma $-aluminum oxide nanotubes and $\gamma $-aluminum oxide nanoparticles dispersed within silicone oil were prepared. The relationship between shear stress and shear rate was measured and theoretically simulated by using an extended Bingham model for both the rheological and electrorheological features of these systems. Shear stress and viscosity showed a sharp increase for the aluminum oxide nanotubes suspensions subjected to applied electric fields whereas aluminum oxide nanoparticles suspensions showed a moderate change. It was found that the transition from liquid to solid state (mediated by the applied electric field) can be described by a power law and that for low applied voltages the relationship is almost linear. [Preview Abstract] |
Thursday, March 18, 2010 1:39PM - 1:51PM |
W12.00013: Exploring the phase behavior of microgel suspensions with Neutron Scattering and Hydrostatic Pressure Juan-Jose Lietor-Santos, Urs Gasser, Alberto Fernandez-Nieves Gels are crosslinked-polymeric networks immersed in a solvent, whose size is sensitive to changes in environmental properties such as temperature, pH or light. Microgels are gels in the colloidal domain. The intrinsic particle elasticity allows microgel suspensions to display a very rich phase behavior as opposed to a system of hard spheres in which liquid, crystal and glassy phases are observed depending solely on the volume fraction of the particles. We study the phase behavior of microgel suspensions varying the volume fraction of the system by using the swelling properties of the particles, which we tune using hydrostatic pressure; the use of pressure allows fast particle size changes that occur homogeneously throughout the sample. To characterize the structural and dynamical properties of the system we use Light and Small Angle Neutron Scattering. We observe formation of crystal and glassy phases, reminiscent of the behavior of colloidal hard spheres. However, our data seems to suggest that the suspension polydispersity changes with particle volume fraction; through these changes, the system manages to crystallize and forms glasses with unusual structural features. [Preview Abstract] |
Thursday, March 18, 2010 1:51PM - 2:03PM |
W12.00014: Influence of Boundary Mobility on the Dynamics of Confined Colloidal Suspensions Gary L. Hunter, Kazem V. Edmond, Eric R. Weeks We use fast confocal microscopy to study the influence of interfacial mobility and confinement on the dynamics of dense colloidal suspensions. Experiments on confined molecular super-cooled liquids have shown that hard/immobile boundaries result in an increase in relaxation times relative to bulk measurements, whereas soft/mobile boundaries lead to a decrease in relaxation times. We confine suspensions of PMMA microspheres within emulsion droplets of different sizes, thereby probing the consequences of confinement. By changing the viscosity of the external, continuous phase, we also control the interfacial mobility of our samples. In this way, we separate the two effects and draw comparisons between mobility within colloidal suspensions and molecular liquids. [Preview Abstract] |
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