Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session K16: Mechanics and Non-linear Rheology of Soft Gels I |
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Sponsoring Units: GSOFT Chair: Fred Mackintosh, Rice University Room: 275 |
Wednesday, March 15, 2017 8:00AM - 8:12AM |
K16.00001: Pull out experiment in a granular material Yue Zhang, Robert Behringer For 2D impact experiments by Clark et al., collisions between the intruder and ``force chains'' provided the major drag on an impacting intruder until the intruder was nearly at rest. As a complement to the impact experiment, we consider controlled pre-failure experiments where a buried intruder remains in a granular material under upward loading, and pull-out or failure experiments where a buried intruder is pulled out of a material, starting from rest. We use 2D photoelastic disks, from which circular intruders of different radii are pulled, to visualize this pulling process. We have found a relaxation process of the granular system under constant upward drag force in the pre-failure experiments. During pull-out, we observed that the velocity and acceleration of the intruder follow a linear relationship, as the velocity increases exponentially with time. The curvature of each force chain can be calculated, and those curvatures are found to follow the same distribution function for different intruder sizes and in both the first and last halves of experimental runs. [Preview Abstract] |
Wednesday, March 15, 2017 8:12AM - 8:24AM |
K16.00002: Side-by-side intruders within a granular flow Gabriel Caballero-Robledo, Eli A. Cuellar-Galan, Cesar L. Clemente-Lopez, Carlos Malaga, Francisco J. Mandujano Sanchez, Manuel F. Acevedo-Escalante Lift and drag forces on side-by-side intruders within a granular flow are studied using experiments, numerical simulations and a hydrodynamic model. Regimes of attractive and repulsive lift forces are found as a function of the separation of the intruders and flow velocity. The origin of such forces is investigated by correlating them to differences in the mean value and fluctuations of flow velocity in the regions around the intruders. Numerically, our three dimensional system is studied through Discrete Element Particle simulations adapted to use a Graphics Processing Unit (GPU). The hydrodynamic model that we apply to describe the system is kinetic theory extended for dense granular flow. [Preview Abstract] |
Wednesday, March 15, 2017 8:24AM - 8:36AM |
K16.00003: Inertia and universality of avalanche statistics: the case of slowly deformed amorphous solids Kamran Karimi, Ezequiel Ferrero, Jean-Louis Barrat We report a numerical study on the role of dissipation in the quasi-static flow of amorphous solids [arXiv preprint arXiv:1610.00533 (2016)]. Using a two-dimensional finite-elements based approach, we analyze avalanche size and duration distributions, as well as yielding threshold statistics, at different damping ratios. We show that the overdamped dynamics can be characterized by a set of scale-free statistics which are governed by universal scaling exponents, in quantitative agreement with previous studies. At low damping ratios, however, the range of the scale-free regime diminishes by the emergence of damping-dependent characteristic peaks in the statistics of avalanches. Despite this break-down of universality, we argue that some generic properties of avalanches hold, enabling us to propose new scaling laws in the underdamped limit. [Preview Abstract] |
Wednesday, March 15, 2017 8:36AM - 8:48AM |
K16.00004: Couette shear of an ideal 2D photo-elastic granular system Meimei Wang, Hu Zheng, Jonathan Barés, Dong Wang, Robert Behringe In this study, Couette shear experiments are conducted using 2D photoelastic granular particles, which allows us to apply infinite shear strain to the granular system. We obtain force information st the granular scale using the calibrated photo-elastic grain force response. The whole granular system is density matched in salt solution, which guarantees an ideal 2D system without basal friction between the particles and the table. The viscosity is negligible at the very small shear strain rate (0.017 rpm). This talk will address two main points: i) how does the system reach a jammed state; ii) how does system reach a long term stable state and what are the properties of that state. [Preview Abstract] |
Wednesday, March 15, 2017 8:48AM - 9:00AM |
K16.00005: Yielding and plastic processes in amorphous materials under tension Joyjit Chattoraj, Emanuela Del Gado, C. Corey Hardin, Ramaswamy Krishnan We use numerical simulations of a simple particle model to investigate the non-linear response of amorphous solids to tension and identify a yielding regime associated with high deformation rates. Such regime seems to be associated to a toughening mechanism which is directly related to the emergence of plastic processes and concurrent growth of large but limited gaps. We have characterized the spatio-temporal correlations of the plastic events and recognize several distinctive features similar to the redistribution of the long ranged elastic strain field detected in amorphous solids under shear. We have also found that the gap growth is associated to a progressive alignment of local tensions and that gaps preferentially grow at the interfaces of aligned domains which are basically the locations of orientational stress defects. Interestingly, such findings can be compared with recent experiments on the mechanics of monolayers of endothelial cells, that form semi-permeable inner surfaces of blood vessels, providing new possible hints on its functioning. [Preview Abstract] |
Wednesday, March 15, 2017 9:00AM - 9:12AM |
K16.00006: Correlated Time-Variation of Asphalt Rheology and Bulk Microstructure Adam Ramm, Sakib Nazmus, Amit Bhasin, Michael Downer We use noncontact optical microscopy and optical scattering in the visible and near-infrared spectrum on Performance Grade (PG) asphalt binder to confirm the existence of microstructures in the bulk. The number of visible microstructures increases linearly as penetration depth of the incident radiation increases, which verifies a uniform volume distribution of microstructures. We use dark field optical scatter in the near-infrared to measure the temperature dependent behavior of the bulk microstructures and compare this behavior with Dynamic Shear Rheometer (DSR) measurements of the bulk complex shear modulus $|G^*(T)|$. The main findings are: (1) After reaching thermal equilibrium, both temperature dependent optical scatter intensity ($I(T)$) and bulk shear modulus ($|G^*(T)|$) continue to change appreciably for times much greater than thermal equilibration times. (2) The hysteresis behavior during a complete temperature cycle seen in previous work derives from a larger time dependence in the cooling step compared with the heating step [1]. (3) Different binder aging conditions show different thermal time-variations for both $I(T)$ and $|G^*(T)|$. [1] Ramm, A., \textit{et. al.}.(2016), Journal of Microscopy, 262: 216-225. [Preview Abstract] |
Wednesday, March 15, 2017 9:12AM - 9:24AM |
K16.00007: Rheology of deformable droplet suspension: a lattice Boltzmann study Martina Foglino, Davide Marenduzzo |
Wednesday, March 15, 2017 9:24AM - 9:36AM |
K16.00008: Abstract Withdrawn We investigate the dynamics of freely expanding liquid sheets produced with fluids having different rheological properties, (i) viscoelastic fluids whose linear viscoelastic behavior in the frequency range (0.1$-$100) rad/s can be accounted by a Maxwell model, with characteristic elastic modulus, $G_o$, relaxation time, $\tau$, and zero-shear viscosity, $\eta_0$ = $G_o\tau$ , can be tuned over several orders of magnitude (ii) Newtonian fluids with $\eta_0$ in the range (1$-$1000) mPas. The liquid sheets are produced by impacting a drop of fluid on a small cylindrical solid target. For viscoelastic fluids we show that, when $\tau$ is shorter than the typical lifetime of the sheet ($\sim$ 10 ms), the dynamics of the sheet is similar to that of Newtonian viscous liquids with equal zero-shear viscosity. We provide a semi-empirical approach based on energy conservation to account for the dependence of the maximal expansion of the sheet with $\eta_0$. By contrast, when $\tau$ is longer than the typical lifetime of the sheet, the behavior drastically differs. The sheet expansion is strongly enhanced as compared to that of viscous samples with comparable zero-shear viscosity, but is heterogeneous with the occurrence of cracks, revealing the elastic nature of the viscoelastic fluid. |
Wednesday, March 15, 2017 9:36AM - 9:48AM |
K16.00009: The Effect of Rigid Filament Geometry on Suspension Rheology Matthew Sartucci, Walter Schwenger, Dan Blair, Jeff Urbach Suspensions of stiff, high aspect ratio particles can have dramatic effects on solvent rheology even at low volume fractions. In order to explore methods of enhancing this impact, we investigated how the geometry of suspended particles can be tuned to amplify their rheological effects. We investigated different helical shapes, ranging from straight rods to more tightly wound coils. We used bacterial flagella harvested from Salmonella Typhimurium as our experimental system, and utilized both mutations and environmental factors to access a range of filament geometries. We paired bulk rheology with microscopy to understand the changes in suspension behavior induced by morphological transitions. [Preview Abstract] |
Wednesday, March 15, 2017 9:48AM - 10:00AM |
K16.00010: Molecular Dynamics Simulations of Nanoparticle-Based Rheology Ting Ge, Gary Grest, Michael Rubinstein We perform molecular dynamics simulations of nanoparticles (NPs) in entangled melts of linear polymers and non-concatenated ring polymers to explore NP-based rheology. As in conventional micro-bead rheology, the generalized Stokes-Einstein relation (GSER) is employed to extract an effective stress relaxation function $G_{GSE} \left( t \right)$ from the mean square displacement of NPs. $G_{GSE} \left( t \right)$ for different NP diameters $d$ are compared with the stress relaxation function $G_{GK} \left( t \right)$ obtained from applying the Green-Kubo formula to a pure polymer melt. By comparing $G_{GSE} \left( t \right)$ and $G_{GK} \left( t \right)$, we demonstrate the slip NP-polymer boundary conditions in simulations. For NPs in linear polymers, a plateau in $G_{GSE} \left( t \right)$ emerges as $d$ exceeds the tube diameter $a$ and approaches the entanglement plateau in $G_{GK} \left( t \right)$ with increasing $d$. A complete overlap of $G_{GSE} \left( t \right)$ and $G_{GK} \left( t \right)$ is not observed for the largest $d\approx 3a$, but is anticipated to occur for $d>4a$. The progressive coupling of NPs to the bulk viscoelasticity reflects the intriguing interplay between NPs with $d$ moderately larger than $a$ and the entanglement network. For NPs in ring polymers, as $d$ increases towards the spanning size $R$ of ring polymers, $G_{GSE} \left( t \right)$ approaches $G_{GK} \left( t \right)$ that exhibits no entanglement plateau. The $d$-dependence of the local viscoelasticity probed by NPs indicates the coupling between NPs and the relaxation of ring polymers at larger length and time scales with increasing $d$. Finally, $G_{GSE} \left( t \right)$ and $G_{GK} \left( t \right)$ are anticipated to overlap for $d>3R$, corresponding to the coupling of NPs to the bulk viscoelasticity. [Preview Abstract] |
Wednesday, March 15, 2017 10:00AM - 10:12AM |
K16.00011: Colloid-Colloid Hydrodynamic Interaction Around a Bend in a Quasi-One-Dimensional Channel Christopher Liepold, Ryan Zarcone, Tibor Heumann, Binhua Lin, Stuart Rice We report a study of the correlation between a pair of particles in a colloid suspension in a bent quasi-one-dimensional (q1d) channel as a function of bend angle. As the bend angle becomes more acute, we observe an increasing depletion of particles in the vicinity of the bend and an increase in the nearest-neighbor separation in the pair correlation function for particles on opposite sides of the bend. Further, we observe that the peak value of $D_{12}$, the coupling term in the pair diffusion tensor that characterizes the effect of the motion of particle 1 on particle 2, coincides with the first peak in the pair correlation function, and that the pair separation dependence of $D_{12}$ mimics that of the pair correlation function. We show that the observed behavior is a consequence of the geometric constraints imposed by the single-file requirement that the particle centers lie on the centerline of the channel and the requirement that the hydrodynamic flow must follow the channel around the bend. We find that the correlation between a pair of particles in a colloidal suspension in a bent q1D channel has the same functional dependence on the pair correlation function as in a straight q1D channel when measured in a coordinate system that follows the centerline of the bent channel. [Preview Abstract] |
Wednesday, March 15, 2017 10:12AM - 10:24AM |
K16.00012: “A new method for analyzing high-frequency microrheology data Kengo Nishi, Maria Kilfoil, Christoph Schmidt, Fred Mackintosh Passive microrheology is an experimental technique used to determine the mechanical response of soft materials from the measured fluctuations of micron-sized beads embedded in the medium. In one common approach, one uses the fluctuation-dissipation theorem to obtain the imaginary part of the material response function from the power spectral density of bead displacement fluctuations, while the real part of the response function is calculated using a Kramers-Kronig integral. The high-frequency cut-off of this integral strongly affects the real part of the response function in the high frequency region. To moderate the influence of the high-frequency cut-off, we propose a new analysis method for passive microrheology, using the fluctuation-dissipation theorem in the time domain. To test the validity of this method, we conducted one- and two-particle microrheology experiments, and a systematic numerical error analysis using synthetic data. [Preview Abstract] |
Wednesday, March 15, 2017 10:24AM - 10:36AM |
K16.00013: Dielectric Rheo-SANS: An Instrument for the Simultaneous Interrogation of Rheology, Microstructure and Electronic Properties of Complex Fluids Norman Wagner, Jeffrey Richards, Julie Hipp, Paul Butler In situ measurements are an increasingly important tool to inform the complex relationship between nanoscale properties and macroscopic measurements. For conducting colloidal suspensions, we seek intrinsic relationships between the measured electrical and mechanical response of a material both in quiescence and under applied shear. These relationships can be used to inform the development of new materials with enhanced electrical and mechanical performance. In order to study these relationships, we have developed a dielectric rheology instrument that is compatible with small angle neutron scattering (SANS) experiments. This Dielectric RheoSANS instrument consists of a Couette geometry mounted on an ARES G2 strain controlled rheometer enclosed in a modified Forced Convection Oven (FCO). In this talk, we outline the development of the Dielectric RheoSANS instruments and demonstrate its operation using two systems - a suspension of carbon black particles in propylene carbonate and poly(3-hexylthiophene) organogel - where there is interest in how shear influences the microstructure state of the material. By monitoring the conductivity and rheological response of these materials at the same time, we can capture the entire evolution of the material response to an applied deformation. [Preview Abstract] |
Wednesday, March 15, 2017 10:36AM - 10:48AM |
K16.00014: Tunable shear thickening: from understanding suspen- sion thickening to controlling viscosity on the fly Itai Cohen, Neil Lin, Chris Ness, Meera Ramaswamy, Jin Sun, Mike Cates, Ben Guy, Michiel Hermes, Wilson Poon Whether contact forces play a role in shear thickening of colloidal systems where hydrodynamic contributions are thought to dominate remains highly controversial. By performing shear reversal experiments on silica and latex colloidal particles, we directly measure the hydrodynamic and contact force contributions to the suspension viscosity. We find that contact forces are not only present, but dominate the shear thickening response. More importantly, this finding directly suggests a strategy for active controlling the thickening viscosities of dense suspensions. We demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to two decades on demand. [Preview Abstract] |
Wednesday, March 15, 2017 10:48AM - 11:00AM |
K16.00015: Localized stresses in Shear Thickening Suspensions Vikram Rathee, Daniel Blair, Jeffery Urbach The bulk rheological response of concentrated suspensions is well documented but the microscopic origin of shear thickening remains poorly understood. One challenge is the lack of experimental technique to measure local stresses. Using boundary stress microscopy, we directly measure localized stresses and determine their role in shear thickening. Surprisingly, we do not observe a smoothly increasing uniform local stress during continuous shear thickening, instead we observe that above onset stress, boundary stress microscopy reveals clearly defined regions of localized high stresses. These high stress regions are dynamic, both in space and time, and appear intermittently. As the applied stress is increased, these high stress regions become larger fraction of total surface area. Since the characteristic size of high stress regions is comparable to gap size we speculate that these regions span the system, percolating from top to bottom. Our results suggest that CST arise from increasingly frequent localized discontinuous transition from a low viscosity state to high viscosity state. [Preview Abstract] |
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