Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P14: Emulsions and Foams |
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Sponsoring Units: DFD Chair: Douglas Durian, University of Pennsylvania Room: 315 |
Wednesday, March 18, 2009 8:00AM - 8:12AM |
P14.00001: Measurement of the Force Network in a Dense Emulsion under Shear S. K. Dutta, E. Knowlton, D. L. Blair We have investigated the properties of a dense oil-in-water emulsion under shear stress. Measurements of the jammed emulsion were taken with a customized confocal rheometer, which is capable of acquiring three-dimensional images while simultaneously applying a precise shear. Images acquired deep inside the emulsion are detailed enough to determine the position and shape of individual emulsion droplets. The forces on each droplet were calculated from the deformation due to neighbors, making it possible to link the bulk rheological properties of the emulsion to local structural relaxation and the force distribution measured at the single droplet level. [Preview Abstract] |
Wednesday, March 18, 2009 8:12AM - 8:24AM |
P14.00002: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 8:24AM - 8:36AM |
P14.00003: Flow-Induced Droplet Deformation and Unjamming in Concentrated Emulsions under Large-Amplitude Oscillatory Shear Jung-Ren Huang, Thomas G. Mason We employ the technique of shear oscillation light scattering to study concentrated oil-in-water emulsions subjected to oscillatory shear that causes droplet deformation and restructuring. Three dimensionless scattering intensity anisotropy factors, defined using the primary and secondary Bragg peak intensities, reflect the degree of droplet deformation caused by the applied shear. These factors distinguish the soft-jamming regime, where shear causes positional disorder, from the sliding hexagonally closed-packed layer regime, where shear induces positional order. Furthermore, near and above the jamming limit of spherical particles, the shear-induced droplet structure depends sensitively on the droplet volume fraction and the shear history. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P14.00004: Structure and Rheology of Stimuli-Responsive Pickering Emulsions Dan Ho, Prasad Sarangapani, Yingxi Elaine Zhu Self-assembly of micro-and nano-spheres and their stability at liquid-liquid interfaces are important due to their broad range of applications from emulsion polymerization to heavy oil transportation. In this work, we employ temperature-responsive poly(N-isopropyl acrylamide) (PNIPAM) microspheres to form Pickering emulsions and directly visualize the dynamics and rheology at the droplet interfaces in response to varied temperature using confocal laser scanning microscopy. Destabilization of the interface is observed as increasing temperature across the lower critical solution temperature (LCST) around 42-44 degree C for this system, where the coarsening at the oil-water interface occurs due to the shrinkage of PNIPAM particle size and results in the onset of coalescence of droplets. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P14.00005: Shear Induced Dynamics of Polydisperse Jammed Emulsion Systems Joaquim Clara Rahola, Eric R. Weeks We study polydisperse decane-in-water emulsions at droplet volume fractions ranging from $\phi$ = 0.65 to $\phi$ = 0.9. At such concentrations emulsions are jammed and thus droplet rearrangements are limited. To induce droplet displacements, an oscillatory strain is applied. We use confocal microscopy to track the trajectories of the droplets in real time and space. Almost all the droplets move periodically, but due to the polydispersity many of them move non-affinely as they are pushed around by other droplets. In these glassy suspensions, the motions of nearby droplets are correlated within a characteristic distance. This length is independent of particle volume fraction while it exhibits an increasing trend with increasing strain amplitude. Moreover, despite the disordered structure of our system, droplets' motions are correlated over ranges longer than the average particle diameter. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P14.00006: Colloidal Hydrodynamics with Arbitrary Boundary Conditions Jonathan K. Whitmer, Erik Luijten Hydrodynamic interactions are essential to the understanding of colloidal dynamics. Due to their complexity and computational cost, they are often ignored in simulations. Over the past decade, coarse-grained methods such as Stochastic Rotation Dynamics\footnote{A. Malevanets and R. Kapral, J. Chem.\ Phys. \textbf{112}, 7260 (2000)} (an example of the larger family of Multi-Particle Collision (MPC) methods\footnote{H. Noguchi and G. Gompper, Phys.\ Rev. E \textbf{78} 016706 (2008)}) have been developed to include these interactions efficiently in simulation. To use these methods for the study of self-assembly dynamics of particles with anisotropic surface chemistry, we extend previously implemented methods for stick boundary conditions\footnote{I. Gotze, H. Noguchi, and G. Gompper Phys.\ Rev. E \textbf{76} 046705 (2007)} to arbitrarily slipping surfaces on the curved surfaces of spherical colloids. We present a mapping from an easily tunable simulation parameter onto the slip length as defined by Navier, and discuss the dynamics of anisotropic particles simulated using this method. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P14.00007: Reversible Rayleight-to-MIe Scattering Transition in a Core-Shell Colloidal System Guangnan Meng, Adeline Perro, Vinothan Manoharan We present a study of light scattering from colloidal particles with small polystyrene cores and large shells of poly(\emph{N'}-isopropylacrylamide-\emph{co}-acrylic acid). When swollen in deionize water at room temperature, the shell is nearly index-matched to pure water, and the scattering is dominated by Rayleigh scattering from the polystyrene cores. As we change the solvent condition by increasing temperature or salt concentration, the shell starts to shrink and scatter light. Both the scattering cross section and the forward scattering of the particles increase, characteristic of Mie scatterers. We use optical microscopy, static light scattering and turbidimetry to study this optical transition. Such core-shell particles might be used as aqueous index-matched tracer colloids, as model scatterers for self-assembly studies, or as optical filters with tunable opacity. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P14.00008: Pressure driven foam flow rheology C.D. Jones, K. Nordstrom, D.J. Durian We probe the complex rheology of 3d foams by flowing them through a narrow column. The foam flows upward through one of two vertical rectangular columns with a 4:1 cross-sectional aspect ratio, by bubbling gas through a soapy solution at the base of our apparatus. One column is clear acrylic sheet on all sides, which is slippery to the foam, and results in plug flow. The other column has the narrow surfaces covered with sandpaper, giving them a sticky surface, which creates shear due to the zero velocity boundary condition. As expected, the flow profile between the slippery broad faces is flat, however the profile between the narrow, sticky faces exhibits a curved velocity profile that is strongly dependent on flow rate. We are able to analyze a 2d velocity profile from a 3d bulk system, whereas other recent foam rheology work has been constrained to the 2d system. We employ particle image velocimetry to measure the strain rate, and compute the stress from the pressure drop along the channel, to investigate the local stress-strain relationships in a flowing foam. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P14.00009: Effective temperature of a sheared foam Daniel Valdez-Balderas, Peter Olsson, Stephen Teitel We perform computer simulations of a model for an overdamped, sheared foam in two dimensions at zero temperature. We measure an effective temperature with the use of an embedded oscillator, in manner analogous to experiments done by Abate and Durian on a different system [arXiv:0806.0765v2]. Our oscillator is one of the bubbles in the foam, which, in addition to its interaction with other bubbles, is also subject to a harmonic potential. We define an effective temperature based on the fluctuations in the position of the oscillator. We compare our results to the effective temperatures computed with the use of measurements of the fluctuations of the shear stress and fluctuations of the energy, respectively. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P14.00010: Realization spaces of bubble clusters and coarsening trajectories Bryan Chen, Randall Kamien In the search for a more unified description of the geometry of equilibrium foams, we study the space of all realizations of equilibrium bubble clusters of fixed topology. The geometry of foam is highly constrained due to the area minimization property - in two dimensions, this means that all interfaces must be portions of circles and interfaces intersect in threes at angles of $120^{\circ}$. This results in a finite dimensional space of bubble clusters, and the dynamics of coarsening via gas diffusion induces a vector flow on it. The boundaries and singularities of the realization space may be identified with topological transitions and instabilities in coarsening. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P14.00011: Experimental studies of low-density fluid phases in tunable dipolar colloids Anand Yethiraj, Ning Li, Hugh Newman, Manuel Valera, Ivan Saika-Voivod Experiments of low-density colloidal fluid phases in the presence of an external electric field are presented. We obtain angular order parameters as a function of the applied electric field. When plotted against a dimensionless dipolar strength parameter, the order parameters for different particle sizes fall on a single curve, suggesting that colloids in a fluid phase in the presence of electric fields do indeed interact by an effective point dipolar interaction. We then explore the statistics of particle packings at low-density and extract the experimental compressibilities and equation of state for these dipolar colloids. [Preview Abstract] |
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