Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A30: Colloids: Diffusion and Transport |
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Sponsoring Units: DCMP Chair: Kazem Edmond, New York University Room: 338 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A30.00001: Long range transport of colloids in aqueous solutions Daniel Florea, Sami Musa, Jacques M.R.J. Huyghe, Hans M. Wyss Colloids in aqueous suspensions can experience strong, extremely long range repulsive forces near interfaces such as biological tissues, gels, ion exchange resins or metals. As a result exclusion zones extending over several millimeters can be formed. While this phenomenon has been previously described, a physical understanding of this process is still lacking. This exclusion zone formation is puzzling because the typical forces acting on colloidal particles are limited to much shorter distances and external fields that could drive the particles are absent. Here we study the exclusion zone formation in detail by following the time and distance-dependent forces acting on the particles. We present a simple model that accounts for our experimental data and directly links the exclusion zone formation to an already known physical transport phenomenon. We show that the effect can be tuned by changing the zeta potential of the particles or by varying the species present in the aqueous solution. We thus provide a direct physical explanation for the intriguing exclusion zone formation and we illustrate how this effect can be exploited in a range of industrial applications. [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A30.00002: Transport of charged colloidal particles in a nonpolar solvent in response to an electric field Tina Lin, Thomas Kodger, David Weitz In nonpolar solvents, particle charging is often controlled through the addition of suitable surfactants, which form charge-stabilizing reverse micelles. By combining microfluidics and confocal microscopy, we directly visualize the dynamics of charged colloidal particles in a nonpolar solvent with reverse micelles in response to an external electric field; this enables us to probe the internal electric field as well as the charging properties of the particle solution. We discover some surprising particle behavior: despite a constant applied electric field, particle transport through the fluid is nonlinear and the apparent particle mobility decays in time; subsequently, the charged particles appear to diffuse freely within the bulk solution. We characterize this behavior and find that the charged reverse micelles play a significant role. [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A30.00003: Revisiting Taylor Dispersion: Differential enhancement of rotational and translational diffusion under oscillatory shear Brian Leahy, Desmond Ong, Xiang Cheng, Itai Cohen The idea of Taylor dispersion - enhancement of translational diffusion under shear - has found applications in fields from pharmacology to chemical engineering. Here, in a combination of experiment and simulations, we study the translational and rotational diffusion of colloidal dimers under triangle-wave oscillatory shear. We find that the rotational diffusion is enhanced, in addition to the enhanced translational diffusion. This ``rotational Taylor dispersion'' depends strongly on the strain rate (Peclet number), aspect ratio, and the shear strain, in contradistinction to translational Taylor dispersion in a shear flow, which depends only weakly on strain rate and aspect ratio. This separate tunability of translations and orientations promises important applications in mixing and self-assembly of solutions of anisometric colloids. We discuss the corresponding effect on the structure and rheology of denser suspensions of rod-like particles. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 8:48AM |
A30.00004: Hydrodynamic Behavior of Colloidal Nanorods and Characterization of Length Distributions Carlos Silvera Batista, Constantine Khripin, Xiaomin Tu, Ming Zheng, Jeffrey Fagan Single-walled carbon nanotubes (SWCNTs) are 1D, cylindrical, structures of carbon with long persistence lengths and consistent diameters. In this talk, I will discuss the use of doubly sorted SWCNTs (by buoyancy and length), which are effectively colloidal rods, to explore experimentally the effectiveness of theoretical approximations for the hydrodynamic drag of a freely rotating rod.~ The objective of this work is to establish and validate the use of Analytical Ultracentrifugation (AUC) as a technique to measure the length distribution of rodlike colloidal particles including SWCNT dispersions. This is particularly necessary for applications of nanotube dispersions, as the transport, optical, and thermal properties, as well as the toxicity of SWCNTs have all been demonstrated to depend on the length. Contrary to AFM, the technique most commonly used to measure length distributions, AUC is able to measure the whole population of particles as they exist in liquid phase. I will present measurements and analysis of SWCNT samples with narrow distributions in length, diameter and buoyancy as measured through AUC and compare them against independent measurements conducted with AFM. ~Using this data, the validity of hydrodynamic theory for this application is verified. [Preview Abstract] |
Monday, March 18, 2013 8:48AM - 9:00AM |
A30.00005: Clustering of Attractive Colloids in Flow Ming Han, Jonathan K. Whitmer, Erik Luijten The behavior of colloidal suspensions under flow is important for numerous applications, including direct-write techniques employing ``colloidal ink.'' Here we investigate the behavior of colloids flowing through narrow channels. When colloidal particles experience sufficiently strong attractive interactions, cluster formation and ultimately gelation may result. We employ computer simulations to investigate how the size and structure of these clusters, as well as their distribution in the flow, is influenced by various experimental variables, including flow velocity, attraction strength, fluid viscosity, and channel diameter. These simulations incorporate explicit hydrodynamics through the multiparticle collision dynamics (MPC) algorithm. Particular attention is paid to the role of channel boundaries and to the dimensionless parameters characterizing the suspension. [Preview Abstract] |
Monday, March 18, 2013 9:00AM - 9:12AM |
A30.00006: Measurements of anisotropic Brownian motion of colloidal clusters Jerome Fung, Thomas G. Dimiduk, Rebecca W. Perry, Vinothan N. Manoharan Nonspherical colloidal particles can exhibit anisotropic Brownian motion characterized by different translational and rotational diffusion constants about different particle axes. We discuss measurements of anisotropic translational and rotational diffusion constants in triangular colloidal clusters made from three micron-sized colloidal spheres. We use digital holographic microscopy (DHM) and electromagnetic scattering solutions to image the three-dimensional Brownian motion of isolated clusters. We track the cluster centers of mass with $\sim$20 nm precision and the cluster orientations with an angular resolution of $\sim$0.1 radians. We also use DHM to measure the diffusion of colloidal spheres bound to the surface of an emulsion droplet and show that the sphere behavior differs significantly from diffusion on planar surfaces at long time scales. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A30.00007: Determination of the hydrodynamic friction matrix for various anisotropic particles Daniela Kraft, Raphael Wittkowksi, Hartmut L\"owen, David Pine The relationship between the shape of a colloidal particle and its Brownian motion can be captured by the hydrodynamic friction matrix. It fully describes the translational and rotational diffusion along the particle's main axes as well as the coupling between rotational and translational diffusion. We observed a wide variety of anisotropic colloidal particles with confocal microscopy and calculated the hydrodynamic friction matrix from the particle trajectories. We find that symmetries in the particle shape are reflected in the entries of the friction matrix. We compare our experimentally obtained results with numerical simulations and theoretical predictions. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A30.00008: Enhanced Diffusion in Quasi-Two-Dimensional Suspensions Adar Sonn, Haim Diamant, Yael Roichman We study the Brownian motion of quasi-two-dimensional suspensions of micron-sized particles parallel to a single wall. The dynamics of a suspension near a single wall has two characteristics; the self diffusivity is smaller than in unconfined suspensions, and the hydrodynamic interactions between particles decay with inter-particle distance $r$, as $1/r^3$. We track the motion of silica beads that sediment to the sample floor due to their high density. Screened Coulomb interactions between the bottom glass wall and the heavily charged surface of the beads maintain the beads floating a few hundred nanometers above the wall. We follow the change in the self diffusivity and hydrodynamic interactions as a function of particle area fraction in the sedimented monolayer, $\phi$. As expected, the self diffusion decreases as $\phi$ increases; however, at large $\phi$, we observed an increase in self diffusivity. We also observe strongly correlated motion between particles separated by a distance much larger than their distance from the wall. This long-range hydrodynamic coupling has non-trivial dependence on particles' density. Some possible explanations for these observations will be discussed. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 9:48AM |
A30.00009: Vibrational properties of dense colloidal suspensions with short-range interparticle attraction Martin Iwanicki, Ke Chen, Arjun G. Yodh, Piotr Habdas We investigate vibrational properties of dense colloidal suspensions with short-range attractive particle interactions. Preliminary results show that the so-called boson peak in the attractive glass density of states is weaker than in comparable repulsively-interacting disordered suspensions. Interestingly, the position of the peak shifts to higher frequencies with increasing interparticle attraction strength. The participation ratio, which measures the degree of spatial localization, also shifts to higher frequencies with increasing interparticle attraction. Interestingly, characteristics of quasi-localized modes do not seem to depend on the attraction strength between particles. The observations are consistent with studies in hard-sphere colloidal suspensions where the boson peak frequency decreased with increasing volume fraction, and was understood in the jamming framework. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:00AM |
A30.00010: Dynamics of Repulsing Charged Particles: a Fluorescence Cross-Correlation Spectroscopy Study Jingfa Yang, Ligang Feng, Jiang Zhao, Andeas Best, Hans-Jurgen Butt, Kaloian Koynov Electrostatic interaction controls the stability of charged colloidal particles dispensed in an aqueous solution. In our study, we measured the interaction between charged polystyrene particles by fluorescence cross-correlation spectroscopy (FCCS). Negative correlation function was observed for these repulsing particles and a detailed analysis by Brownian dynamics simulation provided a few important factors of the system: the correlation length at which the interaction dominates and the cage effect in the diffusion of the particles. [Preview Abstract] |
Monday, March 18, 2013 10:00AM - 10:12AM |
A30.00011: Order Preservation Between Brownian Particles Modeled By Langevin Dynamics William Maulbetsch, William Poole, Joseph Bush, Derek Stein We studied the dynamics of two overdamped Brownian particles in an elongational force gradient following their release from some initial separation. Using a modified one-dimensional Langevin equation, we computed the probability that the particles maintain their order as a function of time. The probability approaches unity when the work required to bring the particles together against the force gradient greatly exceeds the thermal energy, $k_BT$. The time window within which the particles are most likely to reverse their order is given by the time to diffuse the initial separation. We apply our theoretical model to the dynamics of DNA monomers approaching the vertex of the Taylor cone in an electrospray ionization mass spectrometer. The likelihood of preserving the sequential order is estimated to be 95\% when the neighboring monomers of a stretched polymer are cleaved within 10 nm of the vertex. The implications of these results to a DNA sequencing strategy will be discussed. [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A30.00012: Eliminating cracking during drying Qiu Jin, Peng Tan, Andrew B. Schofield, Lei Xu When colloidal suspensions dry, stresses build up and cracks often occur - a phenomenon undesirable for important industries such as paint and ceramics. We demonstrate that the two viscoelastic moduli, $G'$ and $G''$, determine the cracking behavior. By adding emulsion droplets into colloidal suspensions, we systematically decrease the storage modulus, $G'$, and increase the importance of the loss modulus, $G''$, and effectively decrease the amount of cracks. At a critical droplet concentration, cracking disappears completely. Furthermore,adding droplets also varies the speed of air invasion and provides a powerful method to adjust drying rate. With the effective control over cracking and drying rate, our experiment may find important applications in many drying and cracking related industrial processes. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A30.00013: Aging in Colloidal Glasses: a comparison between micro and macrorheology Xiaojun Di, Xiaoguang Peng, Gregory McKenna The analogy between colloidal dynamics and the dynamics of molecular glasses remains an important area of study. Of particular interest to our team is the aging responses of the two systems. We have been investigating the dynamics of colloidal systems composed of thermosensitive particles that change diameter upon change of temperature and comparing the behavior to what is expected in molecular glass-formers. In particular, we have found that concentration jumps in these systems mimic three important behaviors of molecular glasses: the intrinsic isotherm, the asymmetry of approach, and memory effect. In our early work, we were able to show, using multispeckle diffusing wave spectroscopy, that although the three signatures are observed in the concentration jump conditions, they are not identical to the observations in molecular glasses. In the present work, in order to get better resolution for the temperature dependent properties, we are employing PNIPAAM/PS particles with core-shell structure to lessen the temperature sensitivity of the system. A series of different particles with different PNIPAAM fractions (different thermal sensitivity) is being investigated and a comparison of the aging between the microrheology and the macrorheology will be made. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A30.00014: When Colloids Can Deform Jie Zhang, Changqian Yu, Sung Chul Bae, Steve Granick Most colloidal systems that have been explored so far are hard-spheres, which limits their phase behavior and other physical properties to be not so rich as atomic and molecular systems. Here we present a new class of soft and deformable microgel colloidal particles with thermo-sensitivity and ability to display autonomous oscillation when driven by special fuels. The deformability, size changes and structure formation of micron-sized poly(NiPAM) particles and dumbbells of polystyrene-poly(NiPAM) interpenetrating networks can be imaged in situ and analyzed. Other mechanical and other physical properties attributable to deformability can be measured. [Preview Abstract] |
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