Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F18: Emulsions and Foams |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Stephan Koehler, Harvard University Room: 403 |
Tuesday, March 4, 2014 8:00AM - 8:12AM |
F18.00001: Elastic turbulent-like flow of disordered solid composed of polydisperse emulsion drops Peter Yunker, Shima Parsa, Stephan Koehler, David Weitz We experimentally study the low Reynolds number flow of polydisperse emulsion drops through a wide microfluidic channel. Water drops dispersed in oil flow through a microfluidic channel that is 50 microns in height and 1700 microns in width. The drop area fraction is $\sim0.50$, and drop size polydispersities range from 5\% to 40\%. Polydisperse drops are observed to form solid-like plugs in the middle of the channel. These solid plugs of polydisperse drops are squeezed by faster moving oil at the channel edges; in response, the polydisperse drops collectively deform, forming long-lived force chains that resist the faster moving oil. Conversely, monodisperse drops do not form solid-like plugs or long-lived force chains, but instead spread throughout the channel. Surprisingly, the speed fluctuations for flows of polydisperse drops are nonperiodic, and exhibit power-law-like spectral decays similar to those seen in elastic turbulence; for flows of monodisperse drops, the spectra are largely flat. Decreasing interfacial tension causes force chains in flows of polydisperse drops to decrease in size, as drops deform individually rather than collectively. [Preview Abstract] |
Tuesday, March 4, 2014 8:12AM - 8:24AM |
F18.00002: Experimental measurements of stress redistribution in flowing emulsions Eric Weeks, Kenneth Desmond We study how local rearrangements alter droplet stresses within flowing dense quasi-two-dimensional emulsions at area fractions $\phi > 0.87$. Using microscopy, we measure droplet positions while simultaneously using their deformed shape to measure droplet stresses. We find that rearrangements alter nearby stresses in a quadrupolar pattern: stresses on neighboring droplets tend to either decrease or increase depending on location. The stress redistribution is more anisotropic with increasing $\phi$. The spatial character of the stress redistribution influences where subsequent rearrangements occur. Our results provide direct quantitative support for rheological theories of dense amorphous materials that connect local rearrangements to changes in nearby stress. [Preview Abstract] |
Tuesday, March 4, 2014 8:24AM - 8:36AM |
F18.00003: Influence of interfacial area on the rheological behavior of heavy oil emulsions Enrique Soto, Patsy V. Ram\'Irez-Gonz\'alez, Roc\'Io G. de la Torre, Jos\'e M. Guadarrama-Cetina, Sergio H. Qui\~nones-Cisneros Experimental observations of the rheological behavior of heavy oil emulsions ARE presented. The emulsions were prepared from mixtures of the oil and brine in different rations and controlled mixing conditions. It was observed that the oil is the continuous phase and the brine the dispersed one. The drop size distribution and water fraction were measured from digital images obtained by a camera and a microscopy. The viscosity of the emulsions increases, when the drop size decreases and The interfacial area increases. The fluid exhibits a shear thinning and elastic rheological behavior below a critical drop size and concentration. The emulsions are stable for long periods of time. The increase in viscosity and non Newtonian behavior are strongly related to the interfacial area. [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 8:48AM |
F18.00004: Towards an easy way to fabricate small clusters with microfluidic device Bingqing Shen, Mathilde Reyssat, Patrick Tabeling We present a novel approach of clusters elaboration by utilizing microfluidic devices with a T junction combined with a step emulsification generator. The droplets in colloidal size can be directly assembled into clusters in a reproducible manner within a shear flow environment. The shear stress is evidenced to influence the clusters morphology: at low shear, the clusters adopt equilibrium configurations that maximize the number of contact points, consistently with observations made in fluids at rest; at high shear, diverse non-equilibrium configurations are observed. [Preview Abstract] |
Tuesday, March 4, 2014 8:48AM - 9:00AM |
F18.00005: Ternary liquid mixtures control the multiplicity, shape and internal structure of emulsion droplets Martin F. Haase, Jasna Brujic It is important to control the shape, internal structure and stability of emulsion droplets for drug delivery, biochemical assays, and the design of materials with novel physical properties. Successful methods involve the mechanical manipulation of the flow of oil in water using complex microfluidic devices to make multiple emulsions with a sequential introduction of specific reactants. Instead, here we show how the thermodynamics of immiscible liquid mixtures tailor emulsions using a single dripping instability. For example, the initial composition and choice of surfactant govern the multiplicity of concentric alternating oil and water layers inside the droplets. Stabilizing ternary droplets using nanoparticles gives rise to a plethora of shapes whose geometry is defined by the deformability of the shell and the flow rate. Another option is to incorporate lipids to the multiple emulsion droplet, which form vesicles upon expulsion of the inner water droplets. Depending on the number of initial water droplets, these vesicles eventually form complex hollow topologies, which can be used as junctions or scaffolds for the self-assembly of colloidal particles in the future. [Preview Abstract] |
Tuesday, March 4, 2014 9:00AM - 9:12AM |
F18.00006: Theoretical Analysis for the Optical Shaping of Emulsion Droplets David Tapp, Jonathan Taylor, Alex Lubanksy, Colin Bain, Buddhapriya Chakrabarti Motivated by recent experimental observations, I discuss a theoretical framework to predict the three-dimensional shapes of optically deformed micron-sized emulsion droplets with ultra-low interfacial tension. The resulting shape and size of the droplet arises out of a balance between the interfacial tension and optical forces. Using an approximation of the laser field as a Gaussian beam, working within the Rayleigh-Gans regime and beyond, and assuming isotropic surface energy at the oil-water interface, the resulting shape equations are numerically solved to elucidate the three-dimensional droplet geometry. A plethora of shapes as a function of the number of optical tweezers, their laser powers and positions, surface tension, initial droplet size and geometry are obtained. Experimentally, two-dimensional emulsion droplet silhouettes have been imaged from above, but their full side-on view has not been observed and reported for current optical configurations. This experimental limitation points to ambiguity in differentiating between droplets having the same two-dimensional projection but with disparate three-dimensional shapes. The model I present elucidates and quantifies this difference for the first time. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F18.00007: Liquid domains of lipid monolayers on the surface of oil-in-water emulsions Lea-Laetitia Pontani, Dylan Bargteil, Martin Haase, Jasna Brujic Immiscible lipids spontaneously decompose into domains, both in cellular membranes and monolayers of amphiphilic films. Here we show that they also form on the surface of oil in water droplets, produced by a microfluidic device. In this case, curvature induced instabilities are balanced by surface tension to produce diverse surface morphologies, such as spots, stripes and hemispheres. Surprisingly, the ternary phase diagram shows that these structures are present even in binary mixtures and can be stable over weeks. We investigate the origin of domain stability by tuning the parameters of the forces that play a role in this process, such as the electrostatic repulsion between the domains, the surface tension of each phase or the size, i.e. the curvature of the droplets. Understanding those mechanisms will not only shed light on the physics of lipid domains in biological membranes but will also allow us to tune this stability to produce droplets with a given number of patches that can then be functionalized for self-assembly with controlled valency. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F18.00008: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F18.00009: Similarity between humans and foams in aging dynamics Byung Mook Weon, Peter S. Stewart Foams are cellular networks between two immiscible phases. Foams are initially unstable and finally evolve toward a state of lower energy through sequential coalescences of bubbles. In physics, foams are model systems for materials that minimize surface energy. We study coalescence dynamics of clean foams using numerical simulations with a network model. Initial clean foams consist of equally pressurized bubbles and a low fraction of liquid films without stabilizing agents. Aging of clean foams occurs with time as bubbles rapidly coalesce by film rupture and finally evolve toward a new quasi-equilibrium state. Here we find that foam aging is analogous to biological aging: the death rate of bubbles increases exponentially with time, which is similar to the Gompertz mortality law for biological populations. The coalescence evolution of foams is self-similar regardless of initial conditions. The population change of bubbles is well described by a Boltzmann sigmoidal function, indicating that the foam aging is a phase transition phenomenon. This result suggests that foams can be useful model systems for giving insights into biological aging. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F18.00010: Foam morphology, frustration and topological defects in a Negatively curved Hele-Shaw geometry Adil Mughal, Gerd Schroeder-Turk, Myfanwy Evans We present preliminary simulations of foams and single bubbles confined in a narrow gap between parallel surfaces. Unlike previous work, in which the bounding surfaces are flat (the so called Hele-Shaw geometry), we consider surfaces with non-vanishing Gaussian curvature. We demonstrate that the curvature of the bounding surfaces induce a geometric frustration in the preferred order of the foam. This frustration can be relieved by the introduction of topological defects (disclinations, dislocations and complex scar arrangements). We give a detailed analysis of these defects for foams confined in curved Hele-Shaw cells and compare our results with exotic honeycombs, built by bees on surfaces of varying Gaussian curvature. Our simulations, while encompassing surfaces of constant Gaussian curvature (such as the sphere and the cylinder), focus on surfaces with negative Gaussian curvature and in particular triply periodic minimal surfaces (such as the Schwarz P-surface and the Schoen's Gyroid surface). We use the results from a sphere-packing algorithm to generate a Voronoi partition that forms the basis of a Surface Evolver simulation, which yields a realistic foam morphology. [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F18.00011: Testing for Hyperuniformity in Two Dimensional Foam Anthony Chieco, Douglas Durian, Salvatore Torquato It has been conjectured that all maximally random, strictly jammed, saturated systems are hyperuniform, i.e. the standard deviation of the number, N, of particles inside a region goes like the square root of the number, N\textunderscore b, of particles on the boundary. By contrast, for a normal system the standard deviation of N goes like the square root of N. We study a two dimensional dry foam, which is a heterogeneous media that is jammed and therefore should be hyperuniform. For foam, images are taken so that the grayscale values are high in the liquid phase and zero in the gas phase. To test for hyperuniformity, grayscale values are then considered as proxy for the number of particles in each pixel. We probe our system by randomly placing many windows throughout an image to find an average number, \textless N\textgreater , of particles for the whole sample and calculate the standard deviation of N for each set of windows. Our preliminary results show that the system appears closer to normal than hyperuniform but we are examining larger sample sizes in order to get a definitive conclusion. [Preview Abstract] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F18.00012: Diagnosing the hyperuniformity of two-dimensional jammed packings of spheres Remi Dreyfus, Ye Xu, Salvatore Torquato, Arjun Yodh In the colloidal domain, ascertaining the degree to which disordered jammed structures are hyperuniform is gaining interest because the hyperuniformity property (vanishing of infinite-wavelength density fluctuations) seems to endow the jammed structure with novel physical properties. Indeed, it has recently been shown that hyperuniform disordered structures can be produced to exhibit a complete photonic bandgap. However, determining whether a 2D packing of spheres is hyperuniform or not is non-trivial, especially from experimental datasets where imperfection exists. In this talk, we will use numerical simulations and experimental investigations to show how we can diagnose whether a packing is hyperuniform or not. [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F18.00013: Swelling/deswelling of Toroidal Hydrogels Ya-Wen Chang, Michael Dimitriyev, Samantha Marquez, Paul Goldbart, Alberto Fernandez-Nieves Swelling/deswelling of hydrogel spheres proceeds with the increase/decrease of particle radius that corresponds to the change in overall volume. When the hydrogel has a toroidal geometry, which is characterized by two principal radii --radius from the center of the donut hole to the center of the tube, and the tube radius, it is not obvious how swelling proceeds. We prepare thermo-sensitive poly(N-isopropylacrylamide) pNIPAM toroidal gel particles of different aspect ratios. At equilibrium deswelling, i.e., slow heating rate, we find that the aspect ratio remains constant for both fat and thin tori. This is explained by linear elasticity. On the other hand, when the heating rate is sufficiently high, the toroid buckles due to the presence of a water-impermeable skin layer that develops in the initial deswelling stages. [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F18.00014: Deriving the microstructural parameters of sea foam from experimental measurements Wai Soen Chan, Hon Ping Lee, Kin Wah Yu We have studied the effective dielectric constant of sea foam by exploiting its spectral structure. We have considered sea foam as a two-phase composite containing air and sea water, at scale where the quasi-static limit is valid. McPhedran and co-workers derived tight bounds of the structural parameters of such composite when a set of measured data is given. However, determining the exact structural parameters have not been successful. We have performed an inverse algorithm, attempted to determine the structure of the foam given measured data of dielectric constant. We model the sea foam by a multilayered Hashin-Shtrikman structure consisting of air embedded in sea water with decreasing air volume fraction from the top to bottom. We first express the effective permittivity of the foam using spectral representation as proposed by Bergman and Milton. Then, by an optimization approach, we determine the spectral parameters, namely the zeros and poles. Next, we convert these spectral parameters into structural parameters by an algorithm proposed by Sun and Yu. Hence the structure of foam could be determined. The inverse problem of determining the sea foam structure is important in marine science. Sea surface wind speed and salinity could be determined from properties of sea foam. [Preview Abstract] |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F18.00015: Evidence of nanobubbles in alcohol-water mixtures via production of optically-induced breathing modes in nanofluids Luat T. Vuong, J.-Luis Dominguez-Juarez, Matthew Moocarme When light of sufficient intensity enters a liquid close to a meniscus, thermal and mechanical effects lead to the spontaneous formation of ``leaky-faucet'' breathing modes. The modes are also associated with Marangoni convection. We have recently studied these modes in highly disperse solutions containing 80-nm gold plasmonic spheres (0.01mg/mL fill factor) in alcohol-water mixtures. Our investigations are focused on characterizing and understanding the dynamically-coupled light, heat, and electrical currents that are produced via the ``osmotic stress'' of hydration and solvation. The materials of focus are plasmonically-absorbing gold and silver nanoparticles in \textit{alcohol-water mixtures }because it has been observed that the robust breathing modes occur in such nanofluids with extremely low-power light illumination (\textless 50 mW). In addition to new nonlinear dynamics associated with the anomalous physical properties of alcohol-water mixtures-- i.e., partial molar volume, adiabatic compressibility, heat capacity , ultrasonic speed, and light scattering-- we observe evidence of the formation of nanobubbles, which agree with recent hypotheses that alcohol organic-aqueous mixtures form local 100-nm inhomogeneities described as nanobubbles. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700