110,017 research outputs found
Nonlocal Granular Rheology: Role of Pressure and Anisotropy
We probe the secondary rheology of granular media, by imposing a main flow
and immersing a vane-shaped probe into the slowly flowing granulate. The
secondary rheology is then the relation between the exerted torque T and
rotation rate \omega of our probe. In the absence of any main flow, the probe
experiences a clear yield-stress, whereas for any finite flow rate, the yield
stress disappears and the secondary rheology takes on the form of a double
exponential relation between \omega and T. This secondary rheology does not
only depend on the magnitude of T, but is anisotropic --- which we show by
varying the relative orientation of the probe and main flow. By studying the
depth dependence of the three characteristic torques that characterize the
secondary rheology, we show that for counter flow, the dominant contribution is
frictional like --- i.e., T and pressure are proportional for given \omega ---
whereas for co flow, the situation is more complex. Our experiments thus reveal
the crucial role of anisotropy for the rheology of granular media.Comment: 6 pages, 5 figure
Rheology and Contact Lifetime Distribution in Dense Granular Flows
We study the rheology and distribution of interparticle contact lifetimes for
gravity-driven, dense granular flows of non-cohesive particles down an inclined
plane using large-scale, three dimensional, granular dynamics simulations.
Rather than observing a large number of long-lived contacts as might be
expected for dense flows, brief binary collisions predominate. In the hard
particle limit, the rheology conforms to Bagnold scaling, where the shear
stress is quadratic in the strain rate. As the particles are made softer,
however, we find significant deviations from Bagnold rheology; the material
flows more like a viscous fluid. We attribute this change in the collective
rheology of the material to subtle changes in the contact lifetime distribution
involving the increasing lifetime and number of the long-lived contacts in the
softer particle systems.Comment: 4 page
Shear Banding from lattice kinetic models with competing interactions
Soft Glassy Materials, Non Linear Rheology, Lattice Kinetic models,
frustrated phase separation} We present numerical simulations based on a
Boltzmann kinetic model with competing interactions, aimed at characterizating
the rheological properties of soft-glassy materials. The lattice kinetic model
is shown to reproduce typical signatures of driven soft-glassy flows in
confined geometries, such as Herschel-Bulkley rheology, shear-banding and
histeresys. This lends further credit to the present lattice kinetic model as a
valuable tool for the theoretical/computational investigation of the rheology
of driven soft-glassy materials under confinement.Comment: 8 Pages, 5 Figure
Recommended from our members
Cavitation in soft matter
Cavitation is the sudden, unstable expansion of a void or bubble within a liquid or solid subjected to a negative hydrostatic stress. Cavitation rheology is a field emerging from the development of a suite of materials characterization, damage quantification, and therapeutic techniques that exploit the physical principles of cavitation. Cavitation rheology is inherently complex and broad in scope with wide-ranging applications in the biology, chemistry, materials, and mechanics communities. This perspective aims to drive collaboration among these communities and guide discussion by defining a common core of high-priority goals while highlighting emerging opportunities in the field of cavitation rheology. A brief overview of the mechanics and dynamics of cavitation in soft matter is presented. This overview is followed by a discussion of the overarching goals of cavitation rheology and an overview of common experimental techniques. The larger unmet needs and challenges of cavitation in soft matter are then presented alongside specific opportunities for researchers from different disciplines to contribute to the field
Ultraslow dynamics and stress relaxation in the aging of a soft glassy system
We use linear rheology and multispeckle dynamic light scattering (MDLS) to
investigate the aging of a gel composed of multilamellar vesicles. Light
scattering data indicate rearrangement of the gel through an unusual ultraslow
ballistic motion. A dramatic slowdown of the dynamics with sample age
is observed for both rheology and MDLS, the characteristic relaxation time
scaling as . We find the same aging exponent for both
techniques, suggesting that they probe similar physical processes, that is the
relaxation of applied or internal stresses for rheology or MDLS, respectively.
A simple phenomenological model is developed to account for the observed
dynamics.Comment: 8 pages, 4 figures, Submitted to PR
Soluplus solutions as thermothickening materials for topical drug delivery.
Soluplus is a pharmaceutical excipient used primarily in the manufacture of solid dispersions. The polymer also exhibits interesting rheology in aqueous solution, increasing in viscosity as the solution is warmed. This material could have application topical drug delivery to sites including the skin, vagina, rectum or nasal mucosa, where the increase in viscosity allows for improved retention. However, there exists very little information surrounding this “thermothickening” phenomenon and the effect of solution composition on temperature-dependent rheology. In this study, the effect of soluplus concentration, salt inclusion, ethanol addition, and pH on temperature-dependent rheology was measured. The rheology of the solutions was unaffected by pH over the range tolerated by the skin (pH 4–7), but the inclusion of ethanol rapidly negated the thermothickening effect. “Salting out” of the solutions resulted in a depression of gelation temperatures, and an increase in both storage and loss moduli of the solutions. 30% (w/v) soluplus in 1 M NaCl or KCl was identified as a potential thermothickening agent for topical drug delivery.Peer reviewe
Effects of inertia on the steady-shear rheology of disordered solids
We study the finite-shear-rate rheology of disordered solids by means of
molecular dynamics simulations in two dimensions. By systematically varying the
damping magnitude in the low-temperature limit, we identify two well
defined flow regimes, separated by a thin (temperature-dependent) crossover
region. In the overdamped regime, the athermal rheology is governed by the
competition between elastic forces and viscous forces, whose ratio gives the
Weissenberg number (up to elastic parameters); the
macroscopic stress follows the frequently encountered Herschel-Bulkley
law , with yield stress
\Sigma\_0\textgreater{}0. In the underdamped (inertial) regime, dramatic
changes in the rheology are observed for low damping: the flow curve becomes
non-monotonic. This change is not caused by longer-lived correlations in the
particle dynamics at lower damping; instead, for weak dissipation, the sample
heats up considerably due to, and in proportion to, the driving. By suitably
thermostatting more or less underdamped systems, we show that their rheology
only depends on their kinetic temperature and the shear rate, rescaled with
Einstein's vibration frequency.Comment: Accepted for publication in Phys. Rev. Let
Dramatic effect of fluid chemistry on cornstarch suspensions: linking particle interactions to macroscopic rheology
Suspensions of cornstarch in water exhibit strong dynamic shear-thickening.
We show that partly replacing water by ethanol strongly alters the suspension
rheology. We perform steady and non-steady rheology measurements combined with
atomic force microscopy to investigate the role of fluid chemistry on the
macroscopic rheology of the suspensions and its link with the interactions
between cornstarch grains. Upon increasing the ethanol content, the suspension
goes through a yield-stress fluid state and ultimately becomes a shear-thinning
fluid. On the cornstarch grain scale, atomic force microscopy measurements
reveal the presence of polymers on the cornstarch surface, which exhibit a
co-solvency effect. At intermediate ethanol content, a maximum of polymer
solubility induces high microscopic adhesion which we relate to the macroscopic
yield stress
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