Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A35: Suspensions: ColloidsNon-Newtonian Particles
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Chair: Paulo Arratia, University of Pennsylvania Room: 301 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A35.00001: Hydrodynamic entrainment in micro-confined suspensions and its implications for two-point microrheology Christian Aponte-Rivera, Roseanna N. Zia We study hydrodynamic entrainment in spherically confined colloidal suspensions of hydrodynamically interacting particles as a model system for intracellular and other micro-confined biophysical transport. Modeling of transport and rheology in such materials requires an accurate description of the microscopic forces driving particle motion and of particle interactions with nearby boundaries. We carry out dynamic simulations of concentrated, spherically confined colloids as a model system to study the effect of 3D confinement on entrainment and rheology. We show that entrainment between two tracer particles exhibits qualitatively different functional dependence on inter-particle separation as compared to an unbound suspension, and develop a scaling theory that collapses the concentrated mobility of spherically confined suspensions for all volume fractions and particle to cavity size ratios onto a master curve. For widely separated particles, the master curve can be predicted via a Green's function, which suggests a framework with which to conduct two-point microrheology measurements near confining boundaries. The implications of these results for experiments in micro-confined biophysical systems, such as the interior of eukaryotic cells, are discussed. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A35.00002: The effect of hydrodynamic interactions on the Brownian diffusion of spheroidal particles in a suspension Navaneeth Kizhakke Marath, John Wettlaufer Batchelor (1976) determined the effect of hydrodynamic interactions on the diffusivity of rigid spheres in a suspension. In general, the particles in a colloidal suspension are anisotropic, interact with each other hydrodynamically and exhibit both translational and rotational diffusivities, which underlie the estimates of the particle size and shape from dynamic light scattering experiments. Unlike spheres, the translation of a spheroid is coupled to its rotation. We calculate the effect of hydrodynamic interactions on the rotational and translational diffusivities of rigid spheroids in a suspension in terms of a correction to the diffusivities of rigid spheroidal particles in a suspension to O($nL^3$), where $n$ is the number density of the spheroids and $L$ is their characteristic length.\\ \\ {\bf Reference}: {G. K. Batchelor, Brownian diffusion of particles with hydrodynamic interaction, {\em J. Fluid Mech.} {\bf 74}, 1-29 (1976).} [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A35.00003: In-situ USAXS/SAXS Investigation of Tunable Structural Color in Amorphous Photonic Crystals During Electrophoretic Deposition Scott Bukosky, Joshua Hammons, Jinkyu Han, Megan Freyman, Elaine Lee, Caitlyn Cook, Joshua Kuntz, Marcus Worsley, Thomas Yong Han, William Ristenpart, Andrew Pascall Amorphous photonic crystals (APCs) formed via electrophoretic deposition (EPD) exhibit non-iridescent, angle-independent, structural colors believed to arise from changes in the particle-particle interactions and inter-particle spacing, representing a potential new paradigm for display technologies. However, particle dynamics on nanometer length scales that govern the displayed color, crystallinity, and other characteristics of the photonic structures, are not well understood. In this work, in-situ USAXS/SAXS studies of three-dimensional colloidal particle arrays were performed in order to identify their structural response to applied external electric fields. These results were compared to simultaneously acquired UV-Vis spectra to tie the overall electrically induced structure of the APCs directly to the observed changes in visible color. The structural evolution of the APCs provides new information regarding the correlation between nano-scale particle-particle interactions and the corresponding optical response. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A35.00004: Fracture in Kaolinite clay suspensions Sebastien Kosgodagan Acharige, Douglas J. Jerolmack, Paulo E. Arratia Clay minerals are involved in many natural (landslides, river channels) and industrial processes (ceramics, cosmetics, oil recovery). They are plate shaped charged colloids and exhibit different flow properties than simpler colloids when suspended in a liquid such as thixotropy and shear-banding. kaolinite platelets are non-swelling, meaning that the stacks formed by the platelets do not have water layers, and thus the suspension does not have a sol-gel transition. However, it has been shown that kaolinite suspensions possesses a non-zero yield stress even at low concentrations, indicating that the particles arrange themselves in a structure through attractive interactions. Here, we experimentally investigate the sedimentation of kaolinite suspensions in a Hele-Shaw cell. The sedimentation of these dilute suspensions can display solid behavior like fracture, revealed in cross-polarized light, which is linked to the failure of the weakly-bonded structure (typical yield stress $\sim 10^{-2}\ Pa$). By changing the interaction potential of the particles (by sonication or introducing salts), we show through these sedimentation experiments, how the fracture pattern can be avoided. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A35.00005: Growth and Interaction of Colloid Nuclei Michael-Angelo Lam, Boris Khusid, William Meyer, Lou Kondic We study evolution of colloid systems under zero-gravity conditions. In particular, we focus on the regime where there is a coexistence between a liquid and a solid state. Under zero gravity, the dominating process in the bulk of the fluid phase and the solid phase is diffusion. At the moving solid/liquid interface, osmotic pressure is balanced by surface tension, as well as balancing fluxes (conservation of mass) with the kinematics of nuclei growth (Wilson-Frenkel law). Due to the highly nonlinear boundary condition at the moving boundary, care has to be taken when performing numerical simulations. In this work, we present a nonlinear model for colloid nuclei growth. Numerical simulations using a finite volume method are compared with asymptotic analysis of the governing equation and experimental results for nuclei growth. Novel component in our numerical simulations is the inclusion of nonlinear (collective) diffusion terms that depend on the chemical potentials of the colloid in the solid and fluid phase. The results include growth and dissolution of a single colloidal nucleus, as well as evolution of multiple interacting nuclei. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A35.00006: Testing the paradigms of the glass transition in colloids Roseanna Zia, Jialun Wang, Xiaoguang Peng, Qi Li, Gregory McKenna Many molecular liquids freeze upon fast enough cooling. This so-called glass state is path dependent and out of equilibrium, as measured by the Kovacs signature experiments, i.e. intrinsic isotherms, asymmetry of approach and memory effect. The reasons for this path- and time-dependence are not fully understood, due to fast molecular relaxations. Colloids provide a natural way to model such behavior, owing to disparity in colloidal versus solvent time scales that can slow dynamics. To shed light on the ambiguity of glass transition, we study via large-scale dynamic simulation of hard-sphere colloidal glass after volume-fraction jumps, where particle size increases at fixed system volume followed by protocols of the McKenna-Kovacs signature experiments. During and following each jump, the positions, velocities, and particle-phase stress are tracked and utilized to characterize relaxation time scales. The impact of both quench depth and quench rate on arrested dynamics and “state” variables is explored. In addition, we expand our view to various structural signatures, and rearrangement mechanism is proposed. The results provide insight into not only the existence of an “ideal” glass transition, but also the role of structure in such a dense amorphous system. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A35.00007: Influence of B\'{e}nard-Marangoni instability on the morphology of drying colloidal films Benjamin Sobac, Pierre Colinet, Ludovic Pauchard Film formation by drying of colloidal solutions is a widely used process in many industrial applications. The drying of such a system is a very complex process leading to a sol-gel transition induced by solvent evaporation. The resulting film can even crack and delaminate. In this study, we investigate the drying process of a colloidal suspension with a highly volatile solvent and we show that the resulting pattern of delaminated plates drastically differs from what is usually observed for aqueous colloidal suspensions. Visualization using an IR camera reveals that hexagonal convection cells can develop during the drying of solutions with highly volatile solvent. The convective cells may persist all along the film consolidation. Thus, we highlight the importance of the hydrodynamics during the first phase of strong solvent evaporation and the consequences on the following drying steps. A criterion predicting whether or not B\'{e}nard-Marangoni instability effectively occurs will be discussed [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A35.00008: Stress modeling in colloidal dispersions undergoing non-viscometric flows Benjamin Dolata, Roseanna Zia We present a theoretical study of the stress tensor for a colloidal dispersion undergoing non-viscometric flow. In such flows, the non-homogeneous suspension stress depends on not only the local average total stresslet---the sum of symmetric first moments of both the hydrodynamic traction and the interparticle force---but also on the average quadrupole, octupole, and higher-order moments. To compute the average moments, we formulate a six dimensional Smoluchowski equation governing the microstructural evolution of a suspension in an arbitrary fluid velocity field. Under the conditions of rheologically slow flow, where the Brownian relaxation of the particles is much faster than the spatiotemporal evolution of the flow, the Smoluchowski equation permits asymptotic solution, revealing a suspension stress that follows a second-order fluid constitutive model. We obtain a reciprocal theorem and utilize it to show that all constitutive parameters of the second-order fluid model may be obtained from two simpler linear-response problems: a suspension undergoing simple shear and a suspension undergoing isotropic expansion. The consequences of relaxing the assumption of rheologically slow flow, including the appearance of memory and microcontinuum behaviors, are discussed. [Preview Abstract] |
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