Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W37: Nanocolloids and General Fluids |
Hide Abstracts |
Sponsoring Units: DFD Chair: Eric Dufresne, Yale University Room: LACC 512 |
Thursday, March 24, 2005 2:30PM - 2:42PM |
W37.00001: Volume Fraction Dependence of Droplet Rupturing in Concentrated Nanoemulsions K. Meleson, S. Graves, T.G. Mason We investigate droplet rupturing by extreme shear in concentrated silicone oil-in-water nanoemulsions stabilized by sodium dodecyl sulfate (SDS) surfactant. According to Taylor's prediction for dilute emulsions, the ruptured droplet radius, $a$, varies inversely with the viscosity of the continuous phase. If one assumes that the emulsion's effective viscosity controls the average radius of the ruptured droplets, then emulsions that have larger droplet volume fractions, \textit{$\phi {\rm s}$} would be ruptured by the same shear flow to smaller radii. In stark contrast to this, we find that the average droplet radius actually rises with as \textit{$\phi $} approaches the quiescent maximally random jammed value of 0.64. This is evidence that both droplet rupturing and coalescence occur when concentrated emulsions are subjected to extreme shear. We have also observed phase inversion to an oil-continuous emulsion for \textit{$\phi $} $>$ 0.64. This supports the idea that coalescence occurs as the driving shear breaks thin films between the concentrated oil droplets at high \textit{$\phi $}. In addition, we find that the ruptured droplet size is relatively insensitive to large changes in the oil viscosity inside the droplets. [Preview Abstract] |
Thursday, March 24, 2005 2:42PM - 2:54PM |
W37.00002: Electron Transport between Nanoparticle-Coated Liquid Droplets Sebnem Soyler, Christopher Knutson, Kevin McCarthy, Roy Shenhar, Habib Skaff, Vince Rotello, Todd Emrick, Thomas Russell, Mark Tuominen, Anthony Dinsmore We investigate the electronic properties of nanoparticle-coated liquid droplets. We demonstrate single-electron tunnel junctions assembled in solution, using conducting droplets as electrodes and nanoparticles as quantum dots. Here, we are using functionalized gold or CdSe nanoparticles which spontaneously form a monolayer on approx. 30-micron water droplets suspended in insulating oil. A few droplets form junctions between two Platinum or Gold wires; we apply a bias voltage to the wires and measure the current. Due to the small size of the nanoparticles (a few nanometers), the current exhibits single-electron tunneling effects such as the Coulomb blockade. The effect of photoexcitation of the CdSe particles on the current will be discussed. Liquid droplets provide promising systems for controlled and self-repairing tunnel junctions. Improved understanding of the electrical characteristics may allow inexpensive assembly of a large number of devices with controlled size, symmetry and function. This work is partially supported by NASA. [Preview Abstract] |
Thursday, March 24, 2005 2:54PM - 3:06PM |
W37.00003: Shear Induced Rupturing of Nanoemulsion Droplets in Dilute and Concentrated Surfactant Solutions S. Graves, K. Meleson, T.G. Mason We use high-pressure microfluidic injection to rupture silicone oil-in-water droplets repeatedly down to diameters below 100 nm, thereby creating ``nanoemulsions.'' These droplets are stabilized against coalescence by the surfactant sodium dodecyl sulfate (SDS). We systematically increase the SDS concentration, $C$, from 8 to 1000 mM, and we find a decrease in the droplet radius that follows a power law form:$\left\langle {a_s \left( C \right)} \right\rangle \sim C^{-\alpha }$, where $\alpha $= 1/3, over several decades in $C$ down to an average radius of $\left\langle {a_s } \right\rangle $ = 18 nm. The larger droplet radius at small $C$ may be due to reduced coverage of the deformed droplet surfaces by the surfactant, thereby facilitating shear-induced coalescence. Our observed decrease in the droplet radius deviates from the classical prediction that the radius is inversely proportional to the viscosity of the continuous phase. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W37.00004: Reverse Micelles Enable Strong Electrostatic Interactions of Colloidal Particles in Nonpolar Solvents Eric R. Dufresne, Ming F. Hsu, David A. Weitz We demonstrate that colloidal particles can have surprisingly strong electrostatic interactions in nonpolar environments when ions are solubolized by reverse micelles. We find that particles interact with a screened Coulomb potential consistent with screening lengths from 0.17 to 1.4 $\mu$m and a surface potential, $e\zeta$, of about $4k_BT$. A simple thermodynamic model, relating the structure of the micelles to the equilibrium ionic strength, is in good agreement with both conductivity and interaction measurements. Since dissociated ions are solubolized by reverse micelles, the entropic incentive to charge a particle surface is qualitatively changed, and surface entropy plays an important role. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W37.00005: Anisotropy of Sheared Carbon Nanotube Suspensions Dan Fry, Howard Wang, Erik K. Hobbie We measure the anisotropy of sheared carbon nanotube suspensions for a broad range of concentration, aspect ratio and strain rate using a variety of methods. Our measurements highlight the importance of hydrodynamic excluded-volume interactions in the semi-dilute regime, with scaling in terms of a dimensionless shear rate, or Peclet number. Our results also suggest that such interactions might be exploited to fractionate carbon nanotubes by length in simple shear flow. [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W37.00006: Rotational diffusion of magnetic nanorods in 2D viscous media. A. Anguelouch, N. Capallo, R.L. Leheny, D.H. Reich Recent theory has predicted fundamental changes to the hydrodynamic behavior of an anisotropic colloidal particle when it is confined to a thin fluid film [1]. These predictions potentially impact numerous areas, including the behavior of protein rafts and other structures embedded in biological cell membranes. As an idealized realization of such a system, we have studied the rotational drag on ferromagnetic nanowires in thin films of silicone oil on aqueous surfaces. These nanowires are highly cylindrical particles grown by electrochemical deposition with precisely controllable diameters ranging from 10-500 nm and lengths up to 50 microns. Particle tracking techniques to monitor their response to time-varying magnetic fields enables precise determination of rotational diffusion coefficients as a function of nanowire geometry and the oil film thickness. The scaling of the rotational diffusive behavior with nanowire dimensions permits a direct test of the predicted dimensional crossover. [1]A. J. Levine, T.B. Liverpool, and F.C. MacKintosh, Phys. Rev. E \textbf{69}, 021503 (2004) [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 3:54PM |
W37.00007: Reversible Self- and Directed-Assembly of DNA-Linked Micron-Sized Colloids Olivier Theodoly, Marie-Pierre Valignat, Paul Chaikin, William Russel, John Crocker We present a technique for the directed-assembly and self-assembly of complex, static and dynamic, micron scale structures based on the fine control of specific DNA linkages between particles. The use of DNA links combined with polymer brushes provides ways to regulate the range and magnitude of addressable forces between pairs (and further combinations) of different particles. The self-assembled structure of alternated microbeads as well as the directed assembly, using laser tweezers, is reversible. The key to achieve reversibility is shown to be the control of an extremely small number, 1-3, of bridges between particles. [Preview Abstract] |
Thursday, March 24, 2005 3:54PM - 4:06PM |
W37.00008: Colloidal interactions and self-assembly using DNA hybridization Paul Biancaniello, Anthony Kim, John Crocker The specific binding of complementary DNA strands has been suggested as an ideal method for directing the controlled self-assembly of microscopic objects. Using an optical tweezer method, we have directly measured the attractive interaction and dynamics between DNA-grafted colloidal microspheres. The interactions measured can be modeled in detail with no free parameters, using well-known statistical physics and chemistry, boding well for their application to directed self-assembly. The microspheres' binding dynamics, however, show a surprising power-law scaling that can significantly slow annealing and crystallization. These slow dynamics are due to the lubrication forces in the nanoscale, polymer-filled gap between the spheres. Reducing the density of grafted DNA strands can speeds the dynamics sufficiently to grow small colloidal crystals. [Preview Abstract] |
Thursday, March 24, 2005 4:06PM - 4:18PM |
W37.00009: Square-Well Fluid Monomer-Dimer Mixtures: Structural and Thermodynamic Properties James A. Porter, Jane E.G. Lipson Previous studies of square-well chain fluids using continuum Born-Green-Yvon (BGY) theory have focused solely on the structural and thermodynamic properties of one-component fluids in equilibrium, for which the basic variables are fluid density and temperature. In the case of mixtures, the concentrations of the respective components must also be taken into account, which makes the problem a non-trivial one. In this talk, we propose a method for determining the structure, and thus the thermodynamic properties, of a mixture of monomers and dimers by a series of interconnected BGY equations (to be solved self-consistently). From these, monomer-monomer, monomer-dimer, and dimer-dimer correlation functions are obtained which explicitly account for temperature, the density of each component, and the effects of interactions between the components (concentration dependence). Thermodynamic properties are then calculated and compared with other theoretical approaches and with simulation results. Approximate methods for solving these equations are also discussed, and trends in the refinement of the theory from simpler to more complex approaches are examined. [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W37.00010: On Structural Relaxation in Simple Fluids Tomas Oppelstrup, Babak Sadigh, Srikanth Sastry, Mikhail Dzugutov We suggest a new measure of approach to the ergodic equilibrium for a system of particles. The proposed measure is of purely geometric nature, and it is based on assessing the system's progress in its configuration space. Using this measure on the system of hard spheres, we demonstrate the existence of a universal relation between the diffusion and the structural relaxation in dense liquids which manifests itself as the Stokes-Einstein relation. In the low density regime we find that this universality is broken with the onset of a secondary and slower relaxation process which is density dependant and non-existant in the normal liquid domain. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W37.00011: Three-Dimensional Visualization of an Aging Foam Pamela T Korda, Douglas J Durian We use optical tomography to create three-dimensional images of the structure a dry aqueous foam. This technique enables us to determine the distributions of bubble shapes and sizes, in an update of Matzke's classic experiment. Furthermore, by obtaining successive tomographic images as the foam ages, we can track the evolution of the foam's geometry as it coarsens. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 4:54PM |
W37.00012: Speckle Visibility Spectroscopy and Bubble Rearrangements A. S. Gittings, D. J. Durian We use Speckle Visibility Spectroscopy (SVS) to study bubble rearrangements in aqueous foams. SVS is a new dynamic light scattering technique based upon the visibility of a speckle pattern for a given exposure time [1]. Unlike more traditional dynamic light scattering, such as diffusing wave spectroscopy, the dynamics are determined from an ensemble average over camera pixels. This allows resolution of motion that changes systematically and rapidly with time. Our foam sample is contained within a thick glass cell, one face of which is entirely covered with absorbing black tape. Laser light is both introduced and collected at a 1-mm diameter hole punched in the tape. We use a 50 kHz line scan camera and image several speckles per pixel. Bubble rearrangement velocity is determined from the variance of intensity across pixels vs. exposure time. The duration of bubble rearrangements is easily found from a picture plot of pixel visibility as the foam ages. [1] Speckle Visibility Spectroscopy and Variable Granular Fluidization P. K. Dixon and D. J. Durian, Phys. Rev. Lett. 90, 184302 (2003) [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:06PM |
W37.00013: The Role of Confinement-induced Ordering on the Slow Dynamics of Confined Fluids Jianping Gao, W.D. Luedtke, Uzi Landman Grand canonical molecular dynamics simulations have been performed to study molecular diffusion in confined thin liquid films. Thin liquid films (modeled as spherical LJ particles) confined by atomically flat, or rough, gold surfaces are studied, and their properties are compared. This includes layering, in-layer ordering, solvation forces and in-plane molecular diffusion. Atomic-scale roughness, with a rms roughness of about 2 Angstroms, significantly reduces ordering in the confined fluid and quenches the oscillations in the solvation forces. Molecular diffusion remains high for films with a thickness as small as four molecular widths. For atomically flat surfaces where the thin films form well defined layers, sharp slowdown of the molecular diffusion correlates well with the occurrence of in-layer ordering. [Preview Abstract] |
Thursday, March 24, 2005 5:06PM - 5:18PM |
W37.00014: Mode-coupling theory of the enhancement of viscosity by strong confinement G. Ananthakrishna, Moumita Das, Sriram Ramaswamy Experiments ( A. L. Demirel and S. Granick, Phys. Rev. Lett. {\bf 77}, 2261 (1996)) have found that confining a fluid to a thin layer on the scale of a few molecular dimensions leads to a large increase in the apparent shear viscosity and stress relaxation time. We study the ``mode-coupling'' enhancement of viscosity for a simple fluid confined in one direction between parallel walls but free to move in the other two, and show that reducing the confinement thickness slows down the relaxation of density fluctuations in a manner similar to lowering temperature or increasing density. As in bulk fluids, this drives a nonlinear feedback leading to a large increase in the shear viscosity at confining distances $\sim$ a few molecular dimensions. [Preview Abstract] |
|
W37.00015: Breakup of carbon nanotube aggregates in microfluidic traps Steven Hudson, Paul Start, Erik Hobbie, Kalman Migler The critical stress to break aggregates of multiwalled-carbon nanotubes suspended in low-molecular-weight polyisobutylene has been measured in planar elongational flow, produced in a microfluidic device. Through image analysis of aggregates and their fragments, the extension rate of the flow and the size and aspect ratio of the aggregates are measured in real time. While trapping an aggregate at the stagnation point of the planar elongational flow, the flow rate is continually increased, and breaking events are recorded, establishing a correlation of aggregate size and stress. In turn, the number of tubes within an aggregate, estimated from fractal geometry, is approximately proportional to stress$^{-0.66}$. We compare these measurements with clustering and breakup data in simple shear. [Preview Abstract] |
|
W37.00016: Multi-layer microfluidic device to assemble uniform colloidal clusters and double emulsions Steven Hudson, Hua Hu We fabricated a novel multi-layer PDMS microfluidic device, which integrates a valve and a Coulter counter, to prepare uniform colloidal assemblies and double emulsions. First, bonding techniques, such as oxygen plasma and a chemical bonding method, and their effects on the bonding strength between two PDMS layers were investigated systematically by monitoring fracture pressure. Second, in this multi-layer device, we developed a novel valve that can stop flow in a microchannel with arbitrary width and depth. The efficiency and the response of the valve are reported. The in- line Coulter counter signals actuation of the valve to prepare controlled- size colloidal assemblies or double emulsions that contain a uniform number of particles or droplets. These advanced structures are expected to have broad applications and significant impact in optical materials and biomaterials. [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