Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Z9: Complex Fluids, Polymers, Gels |
Hide Abstracts |
Sponsoring Units: DFD Chair: Corey O'Hern, Yale University Room: D220 |
Friday, March 25, 2011 11:15AM - 11:27AM |
Z9.00001: An anisotropic continuum model for flow, aggregation and microstructure evolution in magnetorheological fluids Murat Ocalan, Gareth McKinley The complexities associated with the transport of magnetorheological (MR) fluids under non-uniform magnetic and flow fields pose unresolved problems for generating accurate computational models. The evolutions of the electromagnetic and rheological properties of MR fluids are strong functions of the suspension microstructure; however, the geometrical features that lead to the field non-uniformities are often of a much larger length scale. To address these commonly occurring flow problems, we develop an anisotropic continuum model for MR fluids in which the electromagnetic stress is incorporated into the constitutive model for the viscoplastic stress generated in the bulk fluid by considering the generation and distortion of suspension microstructure under flow. The new model is incorporated into both a single-phase and a two-phase continuum description of the suspension. The aggregation dynamics and the evolution of MR fluid microstructure are observed in unique ferromagnetic microfluidic channels that replicate flow conditions of practical interest. The predictions of the newly developed models are verified with the experimental observations of microstructure evolution and macroscopic measurements of fluid rheology. [Preview Abstract] |
Friday, March 25, 2011 11:27AM - 11:39AM |
Z9.00002: Electrorheological response of dense strontium titanyl oxalate suspensions Carlos Orellana, Jinbo He, Heinrich Jaeger Strontium Titanyl Oxalate (STO) particles were synthesized using a new method of precipitating the STO out of a water solution by adding alcohol. When dispersed in silicon oil, dense STO suspensions exhibit a high static yield stress in the presence of an electric field (200kPa at 5kV/mm), high shear stress at high shear rates and low current densities. We also find that the yield stress increases roughly linearly with applied field. This behavior is a key characteristic of a polar molecule dominated electrorheological effect. We also observed stress stiffening with time under low shear, stress oscillations, and stress reduction with strain. These effects can be accounted for by the interaction of permanent dipoles with the particles, the creation of shear bands of a few particles in width and the lack of self-diffusion in the samples. [Preview Abstract] |
Friday, March 25, 2011 11:39AM - 11:51AM |
Z9.00003: Molecular Simulations of Particle Nanorheology Mir Karim, Rajesh Khare Over the past few years, experimental and theoretical developments in the field of microrheology have enabled determination of the local mechanical properties of complex materials. In this presentation, we will extend this approach to determine the local viscoelastic properties of polymeric materials using molecular dynamics (MD) simulations. Molecular simulations provide the unique ability to explicitly account for the intermolecular interactions in the system. Thus an approach based on molecular simulations allows for the determination of the viscoelastic properties at the nanoscale. The specific system that is studied in this work consists of a polymeric melt in which the polymers are modeled as bead-spring chains. We will present a comparison of the results obtained from the passive and the active nanorheology approaches. A discussion of the parameter (e.g. amplitude and frequency) ranges that allow usage of these techniques will also be presented. [Preview Abstract] |
Friday, March 25, 2011 11:51AM - 12:03PM |
Z9.00004: Microscopic Approach for the Friction on a Spherical Particle in Dense Liquids: Hydrodynamics and Beyond Umi Yamamoto, Kenneth Schweizer We propose a new microscopic, non-mode-coupling, statistical dynamical approach to deriving the Stokes-Einstein (SE) friction coefficient of a large spherical particle dissolved in a dense fluid. The real space method is based on including as a slow variable the force exerted on a particle by the surrounding fluid. By exploiting the appropriate separation of time and length scales, and the Kirkwood superposition approximation for multi-point correlations, the SE result is obtained including the slip and stick limits plus the crossover function. This advance provides the foundation for developing a unified theory of friction for nanoparticles that includes both hydrodynamics and the non-hydrodynamic contribution associated with material-specific particle-fluid and particle-particle forces. Applications to nanoparticles in unentangled and entangled polymer solutions and melts, under various interfacial polymer-particle structure conditions, will be reported. Questions of particular interest include how the non-hydrodynamic friction contribution scales with particle radius, the role of length-scale-dependent viscosity in polymer liquids, and the conditions required for crossover to the hydrodynamics-dominated regime. [Preview Abstract] |
Friday, March 25, 2011 12:03PM - 12:15PM |
Z9.00005: Rheology of bacterial flagella suspensions Sevim Yardimci, Thomas Gibaud, Daniel Chen, Edward Barry, Zvonimir Dogic The mechanical behavior of a suspension of rigid and semiflexible filaments has been studied in great detail. In comparison the effect of the filament geometry has been relatively unexplored. We present experimental results on the rheological behavior of suspensions of curly and straight flagella with an identical average contour length. We find that both suspensions are trapped in a glassy state and exhibit a solid-like behavior. We observe that the scaling of viscoelastic moduli is highly dependent on filament geometry. Taken together, this highlights the role of filament geometry in suspension mechanics. [Preview Abstract] |
Friday, March 25, 2011 12:15PM - 12:27PM |
Z9.00006: Brownian Dynamics simulations of dilute graphene solutions under flow Yueyi Xu, Micah Green Many graphene-based materials (such as thin conductive films and nanocomposites) are processed in the liquid phase and require the conformation and alignment of graphene in solution to be precisely controlled. However, prior studies of conformation dynamics of sheetlike macromolecules such as graphene have been limited to equilibrium behavior, and there have been no studies of the dynamics of sheetlike macromolecules on flow processing timescales. Here we develop Brownian Dynamics (BD) algorithms in order to quantify the effects of flow processing on graphene conformation. The method is conceptually similar to those used for linear polymers; we coarse-grain the sheet using a bead-rod lattice of arbitrary 2-D connectivity and develop a novel theoretical framework for bending and metric forces. Using this technique, we simulate the conformation dynamics of dilute sheetlike macromolecule solutions in shear flow and compute the corresponding solution properties as a function of flow strength, sheet size, and solvent quality. [Preview Abstract] |
Friday, March 25, 2011 12:27PM - 12:39PM |
Z9.00007: Orientation Dependent Gelation of Platelet Suspensions Ya-Wen Chang, Andres Mejia, Zhengdong Cheng Gelling behavior of colloidal suspensions of disk-shaped particles has long been used as an ideal system for studying the formation of arrested state of matter. High aspect ratio synthetic $\alpha $-Zirconium phosphate ($\alpha $--ZrP) monolayer platelets have recently received our attention as a new type of liquid crystal building blocks. We report the phase diagram of charged $\alpha $-Zirconium phosphate platelet suspensions across the isotropic (I) --nematic (N) region versus salt concentrations. Typical electrostatic screening induced flocculation and gelation of platelet suspensions were observed. The morphological and rheological characteristics of liquid crystalline and colloidal gel phases were studied with polarized optical imaging and rotational/oscillatory rheometer. At high ionic strengths ($>$10mM), a re-entrance of fluidic liquid crystal phase occurs when particle volume fractions are above the arrested gel phase. We contribute this behavior to the competition between the driving forces for isotropic/nematic and sol/gel transitions of attractive colloidal platelets. Strong particle alignment hinders gelation, which usually demonstrates the ``house of card'' configuration in platelet suspensions; Isotropic suspensions flocculate and gel easily, as we confirmed experimentally. [Preview Abstract] |
Friday, March 25, 2011 12:39PM - 12:51PM |
Z9.00008: Dynamic separation of macromolecules under temperature gradient Yusuke Maeda, Axel Buguin, Albert Libchaber Thermophoresis is a motion of suspensions in a fluid that are subjected to a temperature gradient. Although its effect is widely studied in case of single solute in water, little is known about how the mixture of different solutes is affected. We heated water with an infrared laser by $\Delta T_{\max } $=5C and $\nabla T$=0.25C/um to induce thermophoresis of polyethylene glycol (PEG) and DNA. PEG is depleted from the hot region and results in a stationary gradient of its high volume fraction $\phi $. Under this high concentration of PEG, DNA of small concentration is submitted to thermophoresis and osmotic pressure difference. The DNA shows regime of depletion, ring-like localization and accumulation as the volume fraction of PEG increases. As the osmotic force depends on the size of trapped solutes, DNA of different size accumulates at different regions. Depending whether the DNA size is below or above 5kbp a different scaling of position versus DNA size is observed. Thermal separation is a general phenomenon. It applies also to RNA and microbeads. [Preview Abstract] |
Friday, March 25, 2011 12:51PM - 1:03PM |
Z9.00009: Non-affine deformations in flexible and semi-flexible polymer gels Anindita Basu, Qi Wen, Xiaoming Mao, Tom Lubensky, Paul Janmey, Arjun Yodh We test the validity of affine deformation assumption in flexible and semi-flexible polymer networks by embedding different-sized fluorescent tracer beads within model polymer networks and quantifying their displacements under shear. A conventional rheometer is used with a confocal microscope for this purpose. Non-affinity is quantified as a function of applied strain, polymer chain density, cross-link concentration, network morphology, reaction kinetics and size of probe particles used. ~Non-affinity measurements in flexible polymer gels are in qualitative agreement with current theories in rubber elasticity. ~For semi-flexible bio-polymer gels, measurements indicate that non-affine deformations are small for networks of thinner, relatively flexible filaments and get smaller as strain increases into non-linear elastic regime. These small measures are consistent with the entropic model for non-linear elasticity of semi-flexible gels. However, as filament stiffness and mesh size increase, the deformations become more non-affine, as predicted by the enthalpic bending and stretching models of non-linear elasticity. [Preview Abstract] |
Friday, March 25, 2011 1:03PM - 1:15PM |
Z9.00010: Drying of polymer films: study of demixing phenomena Julie Fichot, Rodolphe Heyd, Marie-Louise Saboungi, Christophe Josserend, Emilie Combard, Jean Francois Tranchant Understanding the mechanisms that control the stability of polymeric films is important in beauty care. We have prepared films starting from a water-soluble organic polymer, a preservative and water. We study the drying of these films as a function of several physicochemical parameters that control their interfaces such as temperature, humidity and the nature of the support. The viscoelastic properties of the solutions before spreading out are analyzed with a rheometer in order to adjust the temperature. The topography of the films is observed by optical microscopy and the evolution of the drying is determined with a precision gravimetric balance. The behavior of the films on a nanometric scale is followed by AFM. During the drying process, droplets appear on the surface of the film, made up of water surrounded by a shell of preservative. As the films dries, the water evaporates from the droplets and the preservative spreads on the surface of the film, leading to the formation of craters on the surface of the dried film. The dimensions and numbers of the craters depend strongly on the type and concentration of the preservative employed. [Preview Abstract] |
Friday, March 25, 2011 1:15PM - 1:27PM |
Z9.00011: Multiple Particle Collision Dynamics Simulations of the Effect of Catenation on the Structural and Dynamic Properties of Ring Polymers in Solution Govind Hegde, Rajesh Khare Multiple particle collision dynamics (MPCD) is a particle based mesoscale simulation technique that coarse-grains the solvent while preserving the hydrodynamics, thus enabling simulations over longer length and time scales as compared to molecular dynamics (MD) simulations. In this work, MPCD is used to study the effect of topology on the structural and dynamic behavior of complex fluids. The systems of interest in this work are the dilute solutions of ring and catenated ring polymers. MPCD simulation results are compared with those obtained from MD simulations in which the hydrodynamic interactions are governed by the explicit intermolecular interactions. Different chain topologies are considered such as catenated as well as multi-catenated rings. Results will be presented for the effect of chain length on the radius of gyration and chain diffusion coefficient for the various topologies studied. Our results will also be compared with previous theoretical and experimental work reported in literature. [Preview Abstract] |
Friday, March 25, 2011 1:27PM - 1:39PM |
Z9.00012: Strongly anisotropic polymer networks Stephan Ulrich, Annette Zippelius, Panayotis Benetatos We investigate a network of worm-like chains, which are strongly oriented along a preferred direction due to an external field, boundary conditions, or a nematic environment. We discuss the effects of random permanent cross-links, whose density may follow an arbitrary distribution along the alignment direction. We show that the tilt modulus is unaffected by cross-links. As the cross-link density is increased beyond the gel point, the network develops a stiffness to in-plane shear deformations. Results for the shear elasticity and fluctuations of the polymer chains are presented. The case of cross-linking the chains on one end only is highlighted, it constitutes a simple model for polymer brushes. Moreover force-extension curves are presented for a toy model that consists of two cross-linked chains. [Preview Abstract] |
Friday, March 25, 2011 1:39PM - 1:51PM |
Z9.00013: Structure and Dynamics of Water Absorbed in Polyamide Marco Laurati, Paul Sotta, Didier Long, Ludovic Odoni, Veronique Bossenec, Thierry Badel, Arantxa Arbe, Angel Alegria, Juan Colmenero We present results of elastic and inelastic neutron scattering, dielectric spectroscopy and MD simulations concerning the structural organization and the dynamics of water absorbed in an amorphous polyamide material. We find that, different from predictions of available models of water absorption in polyamide, only a small fraction of water binds to the amide groups while most of it organizes into aggregates. Such structural model is supported by results on the microscopic dynamics of water, which can be described as diffusive motions with a relaxation time following a VFT dependence on temperature, similarly to bulk water. Measured average diffusion coefficients of water absorbed in Polyamide are approximately two orders of magnitude smaller than in bulk water, revealing the confinement effect of the polymer matrix. [Preview Abstract] |
Friday, March 25, 2011 1:51PM - 2:03PM |
Z9.00014: Order parameter defining liquid-liquid transition in water J. Raul Grigera, Osvaldo Chara, Andres McCarthy Water presents both open tetrahedral and compact hexagonal structures. Although several order parameters have been proposed to quantify this, all of them are only applicable to data produced by simulation. We present an order parameter ($P_{r})$ that is calculated from the radial distribution function $g(r)$, also available from experiment. We hereby extract the tetrahedral and hexagonal components from the $g(r)$, each one reconstructed as the sum of a Freundlich distribution for the first peak, two subsequent Gaussian distributions, and a sigmoidal to account for the rest. The order parameter can be calculated from the relative contribution of tetrahedral over hexagonal contribution. We obtained the $P_{r}$ for SPC/E water model from molecular dynamics simulations of water at different pressures and temperatures. At 300K, the pressure in which both, tetrahedral and hexagonal contributions become equal ($P_{r }$= 0), a structural crossover is found in the vicinity of 2kbar, close to the pressure at which the `'anomalous'' behavior manifests. Having computed $P_{r}$ for this wide range of pressure and temperature we then calculate the HDL spinodal, the coexistence line, the second critical point, and the Widom line. [Preview Abstract] |
Friday, March 25, 2011 2:03PM - 2:15PM |
Z9.00015: Particle and fluid diffusivity of non-colloidal suspensions Emmanouela Filippidi, Alexandre Franceschini, Chui-Lai Cheung, Jacob Tutmaher, Sean Paradiso, Tarun Jain, David Pine Suspensions of non-colloidal spheres at moderate volume fractions (0.2-0.4) under slow periodic strain undergo a phase transition from an absorbing to an active fluctating state. Particle trajectories change from reversible below the critical strain to irreversible above. We measure the fluid diffusivity of the fluorescently labelled fluid and compare it with the particle diffusivity in order to obtain a measure of the coupling between the two. Of particular interest is how the fluid diffusivity changes near the onset of irreversibility of the particle trajectories. [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