517 research outputs found
Density Functional approach to Nonlinear Rheology
We present a density functional based closure of the pair Smoluchowski
equation for Brownian particles under shear flow. Given an equilibrium free
energy functional as input the theory provides first-principles predictions for
the flow-distorted pair correlation function and associated rheological
quantities over a wide range of volume fractions and flow rates. Taking
two-dimensional hard-disks under shear flow as an illustrative model we
calculate the pair correlation function, viscosity and normal stress difference
under both steady and start-up shear
Dynamical density functional theory analysis of the laning instability in sheared soft matter
Using dynamical density functional theory (DDFT) methods we investigate the
laning instability of a sheared colloidal suspension. The nonequilibrium
ordering at the laning transition is driven by non-affine particle motion
arising from interparticle interactions. Starting from a DDFT which
incorporates the non-affine motion, we perform a linear stability analysis that
enables identification of the regions of parameter space where lanes form. We
illustrate our general approach by applying it to a simple one-component fluid
of soft penetrable particles
From Equilibrium to Steady State: The Transient Dynamics of Colloidal Liquids under Shear
We investigate stresses and particle motion during the start up of flow in a
colloidal dispersion close to arrest into a glassy state. A combination of
molecular dynamics simulation, mode coupling theory and confocal microscopy
experiment is used to investigate the origins of the widely observed stress
overshoot and (previously not reported) super-diffusive motion in the transient
dynamics. A link between the macro-rheological stress versus strain curves and
the microscopic particle motion is established. Negative correlations in the
transient auto-correlation function of the potential stresses are found
responsible for both phenomena, and arise even for homogeneous flows and almost
Gaussian particle displacements.Comment: 24 pages, 14 figures, J. Phys.: Condens. Matter, in pres
Glass Rheology: From mode-coupling theory to a dynamical yield criterion
The mode coupling theory (MCT) of glasses, while offering an incomplete
description of glass transition physics, represents the only established route
to first-principles prediction of rheological behavior in nonergodic materials
such as colloidal glasses. However, the constitutive equations derivable from
MCT are somewhat intractable, hindering their practical use and also their
interpretation. Here, we present a schematic (single-mode) MCT model which
incorporates the tensorial structure of the full theory. Using it, we calculate
the dynamic yield surface for a large class of flows
Structural precursor to freezing: An integral equation study
Recent simulation studies have drawn attention to the shoulder which forms in
the second peak of the radial distribution function of hard-spheres at
densities close to freezing and which is associated with local crystalline
ordering in the dense fluid. We address this structural precursor to freezing
using an inhomogeneous integral equation theory capable of describing local
packing constraints to a high level of accuracy. The addition of a short-range
attractive interaction leads to a well known broadening of the fluid-solid
coexistence region as a function of attraction strength. The appearence of a
shoulder in our calculated radial distribution functions is found to be
consistent with the broadened coexistence region for a simple model potential,
thus demonstrating that the shoulder is not exclusively a high density packing
effect
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