Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D42: Colloids Theory & Computation, Emulsions, and Foams |
Hide Abstracts |
Sponsoring Units: DFD Chair: Eric Weeks, Emory University Room: A302/303 |
Monday, March 21, 2011 2:30PM - 2:42PM |
D42.00001: Liquid loss from foams with low water content Michael Conroy, Justin Taylor, John Farley, James Fleming, Ramagopal Ananth The liquid content of a foam can be significantly affected by liquid loss (drainage), a process that occurs both during and after the foam fills a space. We develop a theoretical model to describe liquid loss and evolution of average liquid volume fraction over time for advancing and static foams. We also perform bench-scale drainage experiments on foams with low water content. The theoretical model shows a constant drainage rate during the filling process which decays exponentially after a static column is formed. The measured loss of liquid is found to be in good agreement with the theoretical predictions. We find that drainage is greatly affected by the time scale for filling a space with foam. Significant effects on drainage are also found by varying bubble size, foam column height, and initial liquid content. The study indicates that drainage behavior can substantially deviate from that described by free-drainage theories, which assume that drainage initiates from a foam of static height. [Preview Abstract] |
Monday, March 21, 2011 2:42PM - 2:54PM |
D42.00002: Molecular Dynamics Study of the Foam Stability of a Mixed Surfactant System with and without Calcium Ions Xiaozhen Yang, Wenhong Yang Foam stability performance of a mixture surfactant system with and without calcium ions, including linear alkylbenzene sulfonate (LAS) and sodium dodecyl sulfate (SDS), has been studied by molecular dynamics. Microscopic interaction analysis reveals that the fraction of free calcium ions, $X_{f}$, in film system indicates the extent of the foam stabilities when $X_{f}$ is in different calcium ion zones. In the system without ions, we found the variable of the surfactant tail mass out of water film, $W$, is indicator of foam stability. Performance of the mixture system predicted here was supported by experiments. [Preview Abstract] |
Monday, March 21, 2011 2:54PM - 3:06PM |
D42.00003: Structural Properties of a Sheared Dense Emulsion S.K. Dutta, E.D. Knowlton, D.L. Blair The flow of a compressed emulsion above its yield point can be described by a velocity profile in addition to a rearrangement of individual droplets on top of this time averaged motion. Using a confocal microscope, we have tracked the droplets of an oil-in-water emulsion as they are sheared in a rheometer. When the applied stress is large, the velocity profile shows a nearly affine deformation, while there is strong strain localization close to yield. The crossover between these two behaviors occurs at higher shear rates as the volume fraction of the droplets is increased. At shorter length scales, rearrangement events are heterogeneously distributed, reflecting the disordered packing of the emulsion droplets. This characterization is a step towards linking bulk viscoelastic properties to local structural relaxation as the system leaves the jammed state. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D42.00004: Janus and Gemini Nanoplates Zhengdong Cheng, Andres Mejia, Ya-wen Chang, Peng He, Agustin Diaz, Abraham Clearfield Janus particles were used to make stable Pickering emulsions (emulsions stabilized by particles). Here we demonstrated a novel method to produce high aspect ratio Janus plates with atomic thickness. Gemini plates with only the edges functionalized are also fabricated. These novel nanoplates are observed to have super surface activity. Most importantly, these particles overcome the two \textit{opposite} effects in the stabilization of Pickering emulsions using spherical particles: stabilization requires particles as small as possible; but smaller particles are easy to escape the interface due to Brownian motion since the adsorption energy to the oil-water interface is proportional to the diameter of the spheres. Our nanoplates have a \textit{large} aspect ratio due to the extremely thin thickness, which offers extraordinary stability to the liquid film between two emulsions to prevent coalescence. In the meantime, their large lateral surface area offers strong adsorption energy at the oil-water interface. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D42.00005: Control over the number, size, and type of inner drops inside a double emulsion Laura Adams, Yuanjin Zhao, Anderson Shum, David Weitz The formation of monodisperse double emulsions, drops inside of drops, has revealed a rich range of configurations not possible without the precise control of microfluidics. Yet-to-date, development of double emulsions with a controlled number of two different inner drops has not emerged. Here we demonstrate exquisite control over the number, size and type of inner drops encapsulated inside a double emulsion. These are fabricated using glass capillary devices implemented with a dual bore injection tube. We will show our latest results and discuss the scientific and technological opportunities made possible by these stable binary configurations. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D42.00006: Yielding and Shear Induced Structure Formation in Emulsions with Attractive Interactions Zhen Shao, Ajay Negi, Chinedum Osuji The yielding behavior of colloidal suspensions is a strong function of inter-particle interactions. Recent results [Pham et al. 2006, 2008] indicate that attractive colloidal glasses display a two-step yielding due to inter-particle bond rupture followed by particle cage escape. From this perspective, we examine the yielding behavior of an oil-in-water emulsion system with attractive interactions using dynamic bulk rheology. In strain sweep experiments, after a limited linear regime, the system yields with a pronounced bump in the viscous modulus, a sharp decrease in the elastic modulus and a crossover between the two. The yielding response is marked by bond-breaking at low volume fractions and bond-breaking accompanied by cage escape above a critical concentration. An increase in the complex modulus is observed at yet higher strains ($>$100{\%}), with both the elastic and viscous components showing small frequency dependent peaks. The onset, peak strains and peak stress display different dependences on volume fraction. We speculate that this display is due to the formation of shear induced structures at high strains and advance a simple model for this behavior. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 3:54PM |
D42.00007: Force Network in a 2D Frictionless Emulsion Model System Kenneth W. Desmond, Pearl Young, Dandan Chen, Eric R. Weeks We confine oil-in-water emulsion droplets between two parallel plates to create a quasi-two-dimensional model system to study the jamming transition. This model system is analogous to granular photoelastic disks with the exception that there is no static friction between our droplets. To study the jamming transition we compress the droplets in small increments and investigate how the force network evolves with increasing area fraction, where the forces are measured using a calibration technique we have developed. The forces in our system are spatial heterogeneous with a probability distribution that is similar to that found for photoelastic disks. We also find that the probability distribution of the forces narrows with area fraction, and that the correlation length of the largest forces is only few particle diameters. [Preview Abstract] |
Monday, March 21, 2011 3:54PM - 4:06PM |
D42.00008: New activated dynamical regimes in dense suspensions of attractive uniaxial colloids Rui Zhang, Kenneth Schweizer Our microscopic theory of cooperative translational-rotational activated glassy dynamics of hard uniaxial particles [PRE,80,011502(2009); JCP,133,104902(2010)] is extended to treat short range attractions. For small aspect ratio dicolloids, a plastic glass (PG) state exists for weak attractions, but is destroyed beyond a critical attraction strength resulting in a new dynamic triple point (fluid, PG, gel), and two novel re-entrant behaviors: PG-fluid-gel, and repulsive glass(RG)-PG-gel. A new mixed ``glass-gel'' state also emerges characterized by center-of-mass and rotational angle localization parameters of intermediate magnitude. At high volume fractions, increasing attraction transforms the RG to an attractive glass (AG) characterized by a dynamic free energy surface with a gel-like localization state but a glass-like saddle point, and a non-monotonic variation of relaxation time and diffusion constant. AG dynamics is of a 2-step nature where physical bonds first break followed by hopping over a glass-like barrier. At high attractions a sharp crossover from a gel to AG with increasing volume fraction is predicted. As the particle aspect ratio grows, the PG state is destroyed, and translational motion becomes increasingly more important for escaping dynamical traps. [Preview Abstract] |
Monday, March 21, 2011 4:06PM - 4:18PM |
D42.00009: A new analysis methodology for the motion of self-propelled particles and its application Young-Moo Byun, Paul Lammert, Vincent Crespi The self-propelled particle (SPP) on the microscale in the solution is a growing field of study, which has a potential to be used for nanomedicine and nanorobots. However, little detailed quantitative analysis on the motion of the SPP has been performed so far because its self-propelled motion is strongly coupled to Brownian motion, which makes the extraction of intrinsic propulsion mechanisms problematic, leading to inconsistent conclusions. Here, we present a novel way to decompose the motion of the SPP into self-propelled and Brownian components; accurate values for self-propulsion speed and diffusion coefficients of the SPP are obtained for the first time. Then, we apply our analysis methodology to ostensible chemotaxis of SPP, and reveal the actual (non-chemotactic) mechanism of the phenomenon, demonstrating that our analysis methodology is a powerful and reliable tool. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D42.00010: Diffraction effects on optical trapping of small particles Rachael Harper, Alex Levine Geometric ray optics is an elegant and computationally efficient means of numerically calculating the forces on particles of arbitrary shape due to their interaction with a beam of light. This method is limited to the regime in which the particle is much larger than the wavelength of light. Ashkin's pioneering work [1] on force exerted by a laser trap on a spherical dielectric particle relies on this geometric optics limit. In current experiments, however, the size of the trapped particles can be comparable to the wavelength of the trapping radiation field. In this talk, we discuss the corrections to ray-tracing-based calculations of the laser trapping forces due to diffraction effects. Specifically, we compare the momentum transfer from a uniform beam of light to hollow dielectric cylindrical shells obtained from two different calculations using: (i) ray-tracing and (ii) the full physical optics formulation. By changing the radii of the inner and outer edges of the hollow cylinder with respect to the wavelength of light we determine the limits of validity of the ray-tracing solution. In the limit in which the radius of the inner cylinder is comparable to the wavelength radiation we show that the corrected momentum transfer is smaller than that predicted by geometric optics. We attribute this result to the reduction in the scattering force on the cylinder due to diffraction effects not accounted for in the geometric optics formalism. [1] A Ashkin, Biophys. J., 61, 569 (1992). [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D42.00011: Capillary Interactions among Spherical Particles at a Curved Liquid Interface Chuan Zeng, Fabian Brau, Benny Davidovitch, Anthony D. Dinsmore Colloidal particles tend to adsorb on liquid interfaces, where in- plane interactions can arise from a variety of mechanisms. We focus on capillary interactions induced by the curvature of the liquid interface, where particles were assumed to have a constant Young-Laplace contact angle at the three-phase contact line. Whereas spherical particles can adsorb on flat or spherical interfaces without deforming the interface, adsorption on a cylindrical interface deforms the interface because of the lack of azimuthal symmetry around the contact line. We present an analytical model of the interfacial shape and energy upon adsorption of a single particle as well as the interaction between two particles. Based on our result on a cylindrical interface, we propose a general formula for the force on a particle on a curved interface. This study provides an important step toward understanding the interactions among interfacial particles when the interface is distorted by an external field. We acknowledge support from the NSF-supported MRSEC on Polymers at UMass (DMR- 0820506) and NSF CBET-0967620. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D42.00012: Slow relaxations of individual colloidal spheres following the breach of a fluid interface Madhav Mani, David M. Kaz, Ryan McGorty, Vinothan N. Manoharan Although the equilibrium state of a micron sized spherical particle at an interface is well understood, the dynamics associated with the approach to equilibrium is not. Recent high-resolution experiments from the Manoharan Lab (Ref: David M. Kaz's Talk) have shown that the dynamics are richer than expected. Subsequent to the initiation of a contact-line at a fluid interface the dynamics towards equilibrium are much slower than predicted by a hydrodynamic theory and the center of mass of the particle appears to follow a logarithmic law in time. We propose the importance of thermally agitated interactions between the contact-line and physical/chemical defects that pin the contact-line locally, thereby leading to an enhancement of the overall dissipation. We deduce that the interface must remain flat during this dynamic process and derive a force-velocity relation, which agrees with both the slow velocities and the logarithmic law. This surprisingly slow approach to equilibrium has significant consequences for processes where interactions between colloids and interfaces are present. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D42.00013: Using Micron-Sized Ellipsoids as a New Tool for Microrheology David Kilgore, Kenneth W. Desmond, Eric R. Weeks It is a well-established principle that the viscosity of a fluid can be calculated by observing the diffusion of microspheres, provided the diameter of the microspheres is known. We are developing a microrheology technique using ellipsoids, where the rheology can be measured without prior knowledge of the length and width of the ellipsoid. The advantage of using ellipsoids is that their asymmetry allows for the diffusion to be decomposed into two translational motions and one rotational motion. For each of these diffusive motions, we can measure a diffusion constant and relate the constant to the three unknowns: the length and width of the ellipsoid, and the viscosity. By measuring the three diffusion constants, we can determine the three unknowns. To verify this technique, we produce ellipsoids in the lab and suspend them in a viscous solution for three-dimensional imaging of the diffusion with a confocal microscope. We are able to get good agreement between the microrheological measurements and macroscopic viscosity measurements. [Preview Abstract] |
Monday, March 21, 2011 5:06PM - 5:18PM |
D42.00014: Inferring elastic properties in colloidal solids: artifacts of a restricted observation window Asad Hasan, Craig Maloney Recently, it has been shown how to extract information about the effective elasticity in colloidal solids, granular packings, {\it etc.}, using two point displacement correlations as obtained in, \emph{e.g.}, optical microscopy experiments or computer simulations. At its core, this technique relies on the observation that, within the harmonic approximation, the Hamiltonian, $H$, is the inverse of the elastic response function, $G$, \emph{defined over the whole domain of the elastic body}. However, most experiments (and even most simulations) have access to G only over some restricted sub-domain of the experimental system. Here, we study restricted observation domains of various size and dimensionality in face centered cubic (fcc) crystals of various size using a pseudo-analytic approach in which $G$ is obtained analytically and is inverted numerically \emph{on a compact sub-domain} to obtain the projected Hamiltonian, $\tilde{H}$. We show that the effective plane-wave energy, $E_k=\langle \psi_k | \tilde{H}| \psi_k \rangle$, for either a [111] or [100] planar subdomain has an unusual dispersion, $E\sim k$, rather than the familiar $E\sim k^2$ and motivate this observation from continuum considerations. We also show how this leads to an anomaly in the density of states of $\tilde{H}$. [Preview Abstract] |
Monday, March 21, 2011 5:18PM - 5:30PM |
D42.00015: Enhancing tracer diffusivity by tuning interparticle interactions and solvation shell structure James Carmer, Gaurav Goel, Tom Truskett Using computer simulations, we explore how tuning the tracer-solvent interactions affects the dynamics of a tracer particle. Optimizing the tracer particle contribution to excess entropy results in significant increases in tracer particle diffusivity. We also observe increases in dynamics while increasing the effective particle size. These changes are investigated at various densities and particle size ratios. [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