Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D50: Focus Session: Dynamic Jamming Fronts and Shear Thickening |
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Sponsoring Units: GSOFT GSNP Chair: Eric Brown, Yale University Room: 218 |
Monday, March 2, 2015 2:30PM - 2:42PM |
D50.00001: Shear thickening and S-shaped flow curves Romain Mari, Ryohei Seto, Jeffrey F. Morris, Morton M. Denn The discontinuous shear thickening (DST) of dense suspensions is a remarkable phenomenon in which the viscosity can increase by several orders of magnitude at a critical shear rate. It follows the phenomenolgy of a first order transition between two ``states'' that we have recently identified as Stokes flows with lubricated or frictional contacts, respectively. Here we extend the analogy further and show the existence of a non-monotonic steady state flow curve by means of stress-controlled simulations, analogous to a non-monotonic equation of state. While we associate DST to an S-shape flow curve, at volume fractions above the shear jamming transition the frictional state loses flowability and the flow curve reduces to an arch, permitting the system to flow only at small stresses. Whereas a thermodynamic transition leads to phase separation in the coexistence region, we observe a uniform shear flow all along the thickening transition. A stability analysis suggests that uniform shear may be mechanically stable for the small Reynolds numbers and system sizes in a rheometer. [Preview Abstract] |
Monday, March 2, 2015 2:42PM - 2:54PM |
D50.00002: Sedimentation of athermal particles in clay suspensions Xavier Clotet, Arshad Kudrolli We discuss sedimentation of athermal particles in dense clay suspensions which appear liquid-like to glass-like. These studies are motivated by the physics important to a diverse range of problems including remediation of oil sands after the extraction of hydrocarbons, and formation of filter cakes in bore wells. We approach this problem by first considering collective sedimentation of athermal spherical particles in a viscous liquid in quasi-two dimensional and three dimensional containers. We examine the system using optical and x-ray tomography techniques which gives particle level information besides global information on the evolution of the volume fraction. Unlike sediments in the dilute limit - which can be modeled as isolated particles that sediment with a constant velocity and slow down exponentially as they approach the bottom of the container - we find interaction between the particles through the viscous fluids leads to qualitatively differences. We find significant avalanching behavior and cooperative motion as the grains collectively settle, and non-exponential increase in settling time. We discuss the effect of stirring caused by the sedimenting particles on their viscosity and consequently the sedimentation rates as a function of particle concentration. [Preview Abstract] |
Monday, March 2, 2015 2:54PM - 3:06PM |
D50.00003: Dynamic jamming fronts in iceberg-choked fjords Ivo Peters, Jason Amundson, Ryan Cassotto, Mark Fahnestock, Kristopher Darnell, Martin Truffer, Wendy Zhang During summertime at the glacier terminus at Jakobshavn Isbr\ae, Greenland, calving events are followed by rapid motion in the ice m\'elange in front of the terminus. Understanding the dynamics of ice m\'elange is important because it acts as a resisting force to calving events. We analyze this motion using time-lapse photography and terrestrial radar images. Large calving events last for approximately 5 minutes, during which $\sim10^{14}$ J of potential energy is released. Motion in the ice m\'elange quickly spreads out over at least 16 km down the fjord, and relaxes in about 1 hour. The ice m\'elange can be viewed as a dense granular system, which is packed close to the jamming point. A jammed ice m\'elange resists expansion of the glacier terminus much more strongly and reduces iceberg calving, which may therefore play a significant role in glacier evolution. In our images, we observe dynamic jamming fronts, which propagate one order of magnitude faster than the instantaneous speed of the calving iceberg. From the ratio between the speed of the front and the calving iceberg we calculate a compaction that agrees with estimated compaction that we observe directly. [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:18PM |
D50.00004: Jamming under rapid pulling in dense granular suspensions Sayantan Majumdar, Ivo R. Peters, Heinrich Jaeger It requires a lot of force to quickly pull out an object immersed in a bath of dense granular suspension like corn starch in water. To understand such striking force response, we experimentally measure the normal force required for pulling out a cylindrical rod vertically from the suspension at a controlled pulling velocity. We observe that for slow pulling velocities the force response is similar to that of highly viscous fluids but above a certain threshold velocity the force show a diverging behavior soon after the initial viscous-like response. The time delay between the initial viscous-like and the diverging force response crucially depends on the proximity of the container walls from the initial contact region of the pulling rod with the suspension. We use in-situ X-ray radiography techniques to map out the local velocity profiles inside the suspension using metallic tracer particles which reveals that the force divergence takes place under pulling when the motion inside the suspension extends up to the container walls. Although the exact mechanism remains to be explained, our experiments suggest that both the magnitude and the delay in force response under pulling are reminiscent of dynamic jamming under impact in dense granular suspensions. [Preview Abstract] |
Monday, March 2, 2015 3:18PM - 3:30PM |
D50.00005: Stress fluctuations in dense granular suspensions Qin Xu, Heinrich Jaeger We experimentally investigate the temporal stress response during steady state shear in dense granular (non-Brownian) suspensions, where the solvent viscosity is varied to tune the frictional and viscous interactions in the system. We focus on the limit where packing fraction is close to the jamming point. For low viscosity suspending liquids, we show that, in the shear thickening regime, shear and normal stresses are highly coupled and exhibit significant fluctuations with time. As shear rate increases, the stress distributions evolve from Gamma to Gaussian distributions. By contrast, for highly viscous solvents, stress fluctuations are greatly reduced and only show Gaussian distributions at different shear rates. Moreover, the fluctuation behaviors are associated with various relaxation modes of the system and therefore lead to different scalings of the power spectral density. By combining the fluctuation analysis in different regimes, we quantitatively show how the interactions between grains affect the suspension dynamics and provide a explanation of why shear thickening becomes weaker in highly viscous solvent. [Preview Abstract] |
Monday, March 2, 2015 3:30PM - 3:42PM |
D50.00006: Dynamics of Concentrated Silica Suspension under Oscillatory Shear Studied by SAXS and XPCS Jonghun Lee, Xiao-Min Lin, Alec Sandy, Suresh Narayanan The viscoelastic properties of complex fluids are often obtained by applying small amplitude oscillatory shear (SAOS). In this regime, their microstructure does not change by shear, and the shear stress linearly responds to the applied strain. However, in the real application, high shear strain or rate is applied, where the viscoelastic properties are affected by the microstructural deformation by this high shear. The rheological behavior of complex fluids under large amplitude oscillatory shear (LAOS) has been widely studied, but there is a lack of studies in microscopic dynamics of complex fluids under LAOS. X-ray scattering is a suitable method to understand microscopic perspective of rheology because of its proper length scales of tens to hundreds nm and time scales of millisecond to thousands second. Here, we studied the dynamics of the concentrated silica nanoparticle suspensions in PEG under different shear strain regimes using small angle x-ray scattering (SAXS) and x-ray photon correlation spectroscopy (XPCS). With strain increasing, these suspensions showed shear thinning and shear thickening behavior, and their microstructural change was observed by SAXS. In oscillatory shear, as the original scattering volume periodically comes back to the original position, we could better study the changes in autocorrelation function by shear and diffusion than steady shear study where correlation decays by transit. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 3:54PM |
D50.00007: Discontinuous shear thickening for frictional granular particles Matthias Grob, Claus Heussinger, Annette Zippelius We study the rheology of frictional granular particles with analytical modelling and numerical simulations in two dimensions. We derive a phase diagram with a topology different from the well known Liu-Nagel phase diagram for frictionless particles with a zero stress critical point. In contrast to the frictionless scenario, jamming first occurs at finite stress at a critical packing fraction $\phi_C$ while a finite yield stress emerges only at $\phi_{\sigma} > \phi_C$. Remarkably, the flow is reentrant and we observe discontinuous shear thickening in the flow curves for $\phi \in (\phi_C, \phi_{\eta})$ with $\phi_{\eta} > \phi_{\sigma}$. All these features can be rationalized with a simple constitutive equation which contains the frictionless scenario as a limiting case. [Preview Abstract] |
Monday, March 2, 2015 3:54PM - 4:06PM |
D50.00008: Material properties of the shear-thickened state in concentrated near hard-sphere colloidal dispersions Norman Wagner, Colin Cwalina Reversible shear thickening is common in concentrated dispersions of Brownian hard-spheres at high shear rates. We confirm the existence of a well-defined colloidal shear-thickened state through experimental measurements of the shear stress and the first and second normal stress differences in the shear-thickened state as a function of the particle volume fraction for a model dispersion of near hard-spheres. The shear stress and normal stress differences are observed to grow linearly with the shear rate in the shear-thickened state and both normal stress differences are observed to be negative. Our experimental results show the shear-thickened state of colloidal dispersions can be described by three material properties---the shear viscosity and first and second normal stress difference coefficients---that are a function of the volume fraction. All three material properties are found to diverge with a power law scaling with the approach to maximum packing,which is found to be 0.54 $\pm$ 0.01. We find the magnitude of the relative shear viscosity is greater than the magnitude of the dimensionless second normal stress difference, which is greater than the magnitude of the dimensionless first normal stress difference. These results are consistent with theoretical predictions for shear thickening by hydrocluster formation and quantitatively comparable to Stokesian Dynamics simulations. We further postulate and show that these material properties are consistent with those measured for non-Brownian suspensions. [Preview Abstract] |
Monday, March 2, 2015 4:06PM - 4:18PM |
D50.00009: The reciprocal effect of lubrication and contact forces in shear-thickening of colloidal suspensions Safa Jamali, Arman Boromand, Joao Maia Recently, the shear-thickening of colloidal suspensions at high shear rates in general, and the so-called discontinuous shear-thickening (DST) in particular, has been attributed to frictional contact forces at high shear rates. This emerging understanding of the contact forces in a suspension has brought back the well-known dilatancy theory which was rather dormant in the past two decades. Here, we study the necessity of short-range hydrodynamics and the correlation between the contact and lubrication forces in shear-thickening suspensions. We use a modified Dissipative Particle Dynamics method that includes squeeze mode lubrication potentials based on the pair drag between two interacting colloids. The effect of simulation parameters and contact potentials on the rheological response of a suspension is studied. Our results show that although the quality of the shear-thickening behavior (whether DST can be obtained or not) is dominated by the contact potentials, the lubrication force is a prerequisite for any type of shear-thickening to be recovered. Needless to mention that this argument is valid for the high P\'{e}clet numbers, as opposed to shear-thinning regime which can be fully reproduced without the need to lubrication or contact potentials. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:54PM |
D50.00010: Dynamic jamming under impact in shear thickening suspensions Invited Speaker: Shomeek Mukhopadhyay Shear thickening fluids such as cornstarch and water show remarkable impact response allowing, for example, a person to run on the surface. We perform constant velocity impact experiments and imaging in shear thickening fluids at velocities lower than 500 mm/s and suspension heights of a few cm. In this regime where inertial effects are insignificant, we find that fronts with a dynamically jammed (DJ) region behind it are generated under impact. When this front and the DJ region reaches the opposite boundary it is able to support large stresses like a solid. These stresses are sufficient to support the weight of a running person. In addition we find a shear thickening transition under impact due to collision of the fronts with the boundary. There is a critical velocity required to generate these impact activated fronts. Using the observations on fronts, DJ region and using energy balance arguments we construct a model to explain the phenomena of running on the surface of cornstarch suspensions. The model shows quantitative agreement with our measurements using high-speed video of running on cornstarch and water suspensions. [Preview Abstract] |
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